## 1. MySQL Connector/J

MySQL provides connectivity for client applications developed in the Java programming language via a JDBC driver, which is called MySQL Connector/J.

MySQL Connector/J is a JDBC-3.0 Type 4 driver, which means that is pure Java, implements version 3.0 of the JDBC specification, and communicates directly with the MySQL server using the MySQL protocol.

Although JDBC is useful by itself, we would hope that if you are not familiar with JDBC that after reading the first few sections of this manual, that you would avoid using naked JDBC for all but the most trivial problems and consider using one of the popular persistence frameworks such as Hibernate, Spring's JDBC templates or Ibatis SQL Maps to do the majority of repetitive work and heavier lifting that is sometimes required with JDBC.

This section is not designed to be a complete JDBC tutorial. If you need more information about using JDBC you might be interested in the following online tutorials that are more in-depth than the information presented here:

- JDBC Basics — A tutorial from Sun covering beginner topics in JDBC

- JDBC Short Course — A more in-depth tutorial from Sun and JGuru

Key topics:

- For help with connection strings, connection options setting up your connection through JDBC, see Section 1.4.1, “Driver/Datasource Class Names, URL Syntax and Configuration Properties for Connector/J”.

- For tips on using Connector/J and JDBC with generic J2EE toolkits, see Section 1.5.2, “Using Connector/J with J2EE and Other Java Frameworks”.

- Developers using the Tomcat server platform, see Section 1.5.2.2, “Using Connector/J with Tomcat”.

- Developers using JBoss, see Section 1.5.2.3, “Using Connector/J with JBoss”.

- Developers using Spring, see Section 1.5.2.4, “Using Connector/J with Spring”.

MySQL Enterprise MySQL Enterprise subscribers will find more information about using JDBC with MySQL in the Knowledge Base articles about JDBC. Access to the MySQL Knowledge Base collection of articles is one of the advantages of subscribing to MySQL Enterprise. For more information see http://www.mysql.com/products/enterprise/advisors.html.

### 1.1. Connector/J Versions

There are currently four versions of MySQL Connector/J available:

- Connector/J 5.1 is current in alpha status. It provides compatibility with all the functionality of MySQL, including 4.1, 5.0, 5.1 and the 6.0 alpha release featuring the new Falcon storage engine. Connector/J 5.1 provides ease of development features, including auto-registration with the Driver Manager, standardized validity checks, categorized SQLExceptions, support for the JDBC-4.0 XML processing, per connection client information, `NCHAR`, `NVARCHAR` and `NCLOB` types. This release also includes all bug fixes up to and including Connector/J 5.0.6.

- Connector/J 5.0 provides support for all the functionality offered by Connector/J 3.1 and includes distributed transaction (XA) support.

- Connector/J 3.1 was designed for connectivity to MySQL 4.1 and MySQL 5.0 servers and provides support for all the functionality in MySQL 5.0 except distributed transaction (XA) support.

- Connector/J 3.0 provides core functionality and was designed with connectivity to MySQL 3.x or MySQL 4.1 servers, although it will provide basic compatibility with later versions of MySQL. Connector/J 3.0 does not support server-side prepared statements, and does not support any of the features in versions of MySQL later than 4.1.

The current recommended version for Connector/J is 5.0. This guide covers all three connector versions, with specific notes given where a setting applies to a specific option.

#### 1.1.1. Java Versions Supported

MySQL Connector/J supports Java-2 JVMs, including:

- JDK 1.2.x (only for Connector/J 3.1.x or earlier)

- JDK 1.3.x

- JDK 1.4.x

- JDK 1.5.x

If you are building Connector/J from source using the source distribution (see Section 1.2.4, “Installing from the Development Source Tree”) then you must use JDK 1.4.x or newer to compiler the Connector package.

MySQL Connector/J does not support JDK-1.1.x or JDK-1.0.x.

Because of the implementation of `java.sql.Savepoint`, Connector/J 3.1.0 and newer will not run on JDKs older than 1.4 unless the class verifier is turned off (by setting the `-Xverify:none` option to the Java runtime). This is because the class verifier will try to load the class definition for `java.sql.Savepoint` even though it is not accessed by the driver unless you actually use savepoint functionality.

Caching functionality provided by Connector/J 3.1.0 or newer is also not available on JVMs older than 1.4.x, as it relies on `java.util.LinkedHashMap` which was first available in JDK-1.4.0.

### 1.2. Connector/J Installation

You can install the Connector/J package using two methods, using either the binary or source distribution. The binary distribution provides the easiest methods for installation; the source distribution enables you to customize your installation further. With either solution, you must manually add the Connector/J location to your Java `CLASSPATH`.

#### 1.2.1. Installing Connector/J from a Binary Distribution

The easiest method of installation is to use the binary distribution of the Connector/J package. The binary distribution is available either as a Tar/Gzip or Zip file which you must extract to a suitable location and then optionally make the information about the package available by changing your `CLASSPATH` (see Section 1.2.2, “Installing the Driver and Configuring the `CLASSPATH`”).

MySQL Connector/J is distributed as a .zip or .tar.gz archive containing the sources, the class files, and the JAR archive named `mysql-connector-java-`[version]`-bin.jar`, and starting with Connector/J 3.1.8 a debug build of the driver in a file named `mysql-connector-java-`[version]`-bin-g.jar`.

Starting with Connector/J 3.1.9, the `.class` files that constitute the JAR files are only included as part of the driver JAR file.

You should not use the debug build of the driver unless instructed to do so when reporting a problem or a bug to MySQL AB, as it is not designed to be run in production environments, and will have adverse performance impact when used. The debug binary also depends on the Aspect/J runtime library, which is located in the `src/lib/aspectjrt.jar` file that comes with the Connector/J distribution.

You will need to use the appropriate graphical or command-line utility to extract the distribution (for example, WinZip for the .zip archive, and tar for the .tar.gz archive). Because there are potentially long filenames in the distribution, we use the GNU tar archive format. You will need to use GNU tar (or an application that understands the GNU tar archive format) to unpack the .tar.gz variant of the distribution.

#### 1.2.2. Installing the Driver and Configuring the `CLASSPATH`

Once you have extracted the distribution archive, you can install the driver by placing `mysql-connector-java-[version]-bin.jar` in your classpath, either by adding the full path to it to your `CLASSPATH` environment variable, or by directly specifying it with the command line switch -cp when starting your JVM.

If you are going to use the driver with the JDBC DriverManager, you would use `com.mysql.jdbc.Driver` as the class that implements java.sql.Driver.

You can set the `CLASSPATH` environment variable under UNIX, Linux or Mac OS X either locally for a user within their `.profile`, `.login` or other login file. You can also set it globally by editing the global `/etc/profile` file.

For example, under a C shell (csh, tcsh) you would add the Connector/J driver to your `CLASSPATH` using the following:

    shell> setenv CLASSPATH /path/mysql-connector-java-[ver]-bin.jar:$CLASSPATH

Or with a Bourne-compatible shell (sh, ksh, bash):

    export set CLASSPATH=/path/mysql-connector-java-[ver]-bin.jar:$CLASSPATH

Within Windows 2000, Windows XP and Windows Server 2003, you must set the environment variable through the System control panel.

If you want to use MySQL Connector/J with an application server such as Tomcat or JBoss, you will have to read your vendor's documentation for more information on how to configure third-party class libraries, as most application servers ignore the `CLASSPATH` environment variable. For configuration examples for some J2EE application servers, see Section 1.5.2, “Using Connector/J with J2EE and Other Java Frameworks”. However, the authoritative source for JDBC connection pool configuration information for your particular application server is the documentation for that application server.

If you are developing servlets or JSPs, and your application server is J2EE-compliant, you can put the driver's .jar file in the WEB-INF/lib subdirectory of your webapp, as this is a standard location for third party class libraries in J2EE web applications.

You can also use the MysqlDataSource or MysqlConnectionPoolDataSource classes in the `com.mysql.jdbc.jdbc2.optional` package, if your J2EE application server supports or requires them. Starting with Connector/J 5.0.0, the `javax.sql.XADataSource` interface is implemented via the `com.mysql.jdbc.jdbc2.optional.MysqlXADataSource` class, which supports XA distributed transactions when used in combination with MySQL server version 5.0.

The various MysqlDataSource classes support the following parameters (through standard set mutators):

- user

- password

- serverName (see the previous section about fail-over hosts)

- databaseName

- port

#### 1.2.3. Upgrading from an Older Version

MySQL AB tries to keep the upgrade process as easy as possible, however as is the case with any software, sometimes changes need to be made in new versions to support new features, improve existing functionality, or comply with new standards.

This section has information about what users who are upgrading from one version of Connector/J to another (or to a new version of the MySQL server, with respect to JDBC functionality) should be aware of.

##### 1.2.3.1. Upgrading from MySQL Connector/J 3.0 to 3.1

Connector/J 3.1 is designed to be backward-compatible with Connector/J 3.0 as much as possible. Major changes are isolated to new functionality exposed in MySQL-4.1 and newer, which includes Unicode character sets, server-side prepared statements, SQLState codes returned in error messages by the server and various performance enhancements that can be enabled or disabled via configuration properties.

- Unicode Character Sets — See the next section, as well as Character Set Support, for information on this new feature of MySQL. If you have something misconfigured, it will usually show up as an error with a message similar to `Illegal mix of collations`.

- Server-side Prepared Statements — Connector/J 3.1 will automatically detect and use server-side prepared statements when they are available (MySQL server version 4.1.0 and newer).

  Starting with version 3.1.7, the driver scans SQL you are preparing via all variants of `Connection.prepareStatement()` to determine if it is a supported type of statement to prepare on the server side, and if it is not supported by the server, it instead prepares it as a client-side emulated prepared statement. You can disable this feature by passing emulateUnsupportedPstmts=false in your JDBC URL.

  If your application encounters issues with server-side prepared statements, you can revert to the older client-side emulated prepared statement code that is still presently used for MySQL servers older than 4.1.0 with the connection property useServerPrepStmts=false

- Datetimes with all-zero components (`0000-00-00 ...`) — These values can not be represented reliably in Java. Connector/J 3.0.x always converted them to NULL when being read from a ResultSet.

  Connector/J 3.1 throws an exception by default when these values are encountered as this is the most correct behavior according to the JDBC and SQL standards. This behavior can be modified using the zeroDateTimeBehavior configuration property. The allowable values are:

  - `exception` (the default), which throws an SQLException with an SQLState of `S1009`.

  - `convertToNull`, which returns `NULL` instead of the date.

  - `round`, which rounds the date to the nearest closest value which is `0001-01-01`.

  Starting with Connector/J 3.1.7, `ResultSet.getString()` can be decoupled from this behavior via noDatetimeStringSync=true (the default value is `false`) so that you can get retrieve the unaltered all-zero value as a String. It should be noted that this also precludes using any time zone conversions, therefore the driver will not allow you to enable noDatetimeStringSync and useTimezone at the same time.

- New SQLState Codes — Connector/J 3.1 uses SQL:1999 SQLState codes returned by the MySQL server (if supported), which are different from the legacy X/Open state codes that Connector/J 3.0 uses. If connected to a MySQL server older than MySQL-4.1.0 (the oldest version to return SQLStates as part of the error code), the driver will use a built-in mapping. You can revert to the old mapping by using the configuration property useSqlStateCodes=false.

- `ResultSet.getString()` — Calling `ResultSet.getString()` on a BLOB column will now return the address of the byte[] array that represents it, instead of a String representation of the BLOB. BLOBs have no character set, so they can't be converted to java.lang.Strings without data loss or corruption.

  To store strings in MySQL with LOB behavior, use one of the TEXT types, which the driver will treat as a java.sql.Clob.

- Debug builds — Starting with Connector/J 3.1.8 a debug build of the driver in a file named `mysql-connector-java-`[version]`-bin-g.jar` is shipped alongside the normal binary jar file that is named `mysql-connector-java-`[version]`-bin.jar`.

  Starting with Connector/J 3.1.9, we don't ship the .class files unbundled, they are only available in the JAR archives that ship with the driver.

  You should not use the debug build of the driver unless instructed to do so when reporting a problem or bug to MySQL AB, as it is not designed to be run in production environments, and will have adverse performance impact when used. The debug binary also depends on the Aspect/J runtime library, which is located in the `src/lib/aspectjrt.jar` file that comes with the Connector/J distribution.

##### 1.2.3.2. JDBC-Specific Issues When Upgrading to MySQL Server 4.1 or Newer

- Using the UTF-8 Character Encoding - Prior to MySQL server version 4.1, the UTF-8 character encoding was not supported by the server, however the JDBC driver could use it, allowing storage of multiple character sets in latin1 tables on the server.

  Starting with MySQL-4.1, this functionality is deprecated. If you have applications that rely on this functionality, and can not upgrade them to use the official Unicode character support in MySQL server version 4.1 or newer, you should add the following property to your connection URL:

  `useOldUTF8Behavior=true`

- Server-side Prepared Statements - Connector/J 3.1 will automatically detect and use server-side prepared statements when they are available (MySQL server version 4.1.0 and newer). If your application encounters issues with server-side prepared statements, you can revert to the older client-side emulated prepared statement code that is still presently used for MySQL servers older than 4.1.0 with the following connection property:

  `useServerPrepStmts=false`

#### 1.2.4. Installing from the Development Source Tree

### Caution

You should read this section only if you are interested in helping us test our new code. If you just want to get MySQL Connector/J up and running on your system, you should use a standard release distribution.

To install MySQL Connector/J from the development source tree, make sure that you have the following prerequisites:

- Subversion, to check out the sources from our repository (available from http://subversion.tigris.org/).

- Apache Ant version 1.6 or newer (available from http://ant.apache.org/).

- JDK-1.4.2 or later. Although MySQL Connector/J can be installed on older JDKs, to compile it from source you must have at least JDK-1.4.2.

The Subversion source code repository for MySQL Connector/J is located at http://svn.mysql.com/svnpublic/connector-j. In general, you should not check out the entire repository because it contains every branch and tag for MySQL Connector/J and is quite large.

To check out and compile a specific branch of MySQL Connector/J, follow these steps:

1. At the time of this writing, there are three active branches of Connector/J: `branch_3_0`, `branch_3_1` and `branch_5_0`. Check out the latest code from the branch that you want with the following command (replacing `[major]` and `[minor]` with appropriate version numbers):

       shell> svn co »
       http://svn.mysql.com/svnpublic/connector-j/branches/branch_[major]_[minor]/connector-j

   This creates a `connector-j` subdirectory in the current directory that contains the latest sources for the requested branch.

2. Change location to the `connector-j` directory to make it your current working directory:

       shell> cd connector-j

3. Issue the following command to compile the driver and create a `.jar` file suitable for installation:

       shell> ant dist

   This creates a `build` directory in the current directory, where all build output will go. A directory is created in the `build` directory that includes the version number of the sources you are building from. This directory contains the sources, compiled `.class` files, and a `.jar` file suitable for deployment. For other possible targets, including ones that will create a fully packaged distribution, issue the following command:

       shell> ant --projecthelp

4. A newly created `.jar` file containing the JDBC driver will be placed in the directory `build/mysql-connector-java-`[version]``.

   Install the newly created JDBC driver as you would a binary `.jar` file that you download from MySQL by following the instructions in Section 1.2.2, “Installing the Driver and Configuring the `CLASSPATH`”.

### 1.3. Connector/J Examples

Examples of using Connector/J are located throughout this document, this section provides a summary and links to these examples.

- Example 1, “Obtaining a connection from the `DriverManager`”

- Example 2, “Using java.sql.Statement to execute a `SELECT` query”

- Example 3, “Stored Procedures”

- Example 4, “Using `Connection.prepareCall()`”

- Example 5, “Registering output parameters”

- Example 6, “Setting `CallableStatement` input parameters”

- Example 7, “Retrieving results and output parameter values”

- Example 8, “Retrieving `AUTO_INCREMENT` column values using `Statement.getGeneratedKeys()`”

- Example 9, “Retrieving `AUTO_INCREMENT` column values using `SELECT LAST_INSERT_ID()`”

- Example 10, “Retrieving `AUTO_INCREMENT` column values in `Updatable ResultSets`”

- Example 11, “Using a connection pool with a J2EE application server”

- Example 12, “Example of transaction with retry logic”

### 1.4. Connector/J (JDBC) Reference

This section of the manual contains reference material for MySQL Connector/J, some of which is automatically generated during the Connector/J build process.

#### 1.4.1. Driver/Datasource Class Names, URL Syntax and Configuration Properties for Connector/J

The name of the class that implements java.sql.Driver in MySQL Connector/J is `com.mysql.jdbc.Driver`. The `org.gjt.mm.mysql.Driver` class name is also usable to remain backward-compatible with MM.MySQL. You should use this class name when registering the driver, or when otherwise configuring software to use MySQL Connector/J.

The JDBC URL format for MySQL Connector/J is as follows, with items in square brackets ([, ]) being optional:

    jdbc:mysql://[host][,failoverhost...][:port]/[database] »
    [?propertyName1][=propertyValue1][&propertyName2][=propertyValue2]...

If the hostname is not specified, it defaults to 127.0.0.1. If the port is not specified, it defaults to 3306, the default port number for MySQL servers.

    jdbc:mysql://[host:port],[host:port].../[database] »
    [?propertyName1][=propertyValue1][&propertyName2][=propertyValue2]...

If the database is not specified, the connection will be made with no default database. In this case, you will need to either call the `setCatalog()` method on the Connection instance or fully-specify table names using the database name (i.e. `SELECT dbname.tablename.colname FROM dbname.tablename...`) in your SQL. Not specifying the database to use upon connection is generally only useful when building tools that work with multiple databases, such as GUI database managers.

MySQL Connector/J has fail-over support. This allows the driver to fail-over to any number of slave hosts and still perform read-only queries. Fail-over only happens when the connection is in an `autoCommit(true)` state, because fail-over can not happen reliably when a transaction is in progress. Most application servers and connection pools set `autoCommit` to `true` at the end of every transaction/connection use.

The fail-over functionality has the following behavior:

- If the URL property autoReconnect is false: Failover only happens at connection initialization, and failback occurs when the driver determines that the first host has become available again.

- If the URL property autoReconnect is true: Failover happens when the driver determines that the connection has failed (before every query), and falls back to the first host when it determines that the host has become available again (after `queriesBeforeRetryMaster` queries have been issued).

In either case, whenever you are connected to a "failed-over" server, the connection will be set to read-only state, so queries that would modify data will have exceptions thrown (the query will never be processed by the MySQL server).

Configuration properties define how Connector/J will make a connection to a MySQL server. Unless otherwise noted, properties can be set for a DataSource object or for a Connection object.

Configuration Properties can be set in one of the following ways:

- Using the set*() methods on MySQL implementations of java.sql.DataSource (which is the preferred method when using implementations of java.sql.DataSource):

  - com.mysql.jdbc.jdbc2.optional.MysqlDataSource

  - com.mysql.jdbc.jdbc2.optional.MysqlConnectionPoolDataSource

- As a key/value pair in the java.util.Properties instance passed to `DriverManager.getConnection()` or `Driver.connect()`

- As a JDBC URL parameter in the URL given to `java.sql.DriverManager.getConnection()`, `java.sql.Driver.connect()` or the MySQL implementations of the `javax.sql.DataSource` `setURL()` method.

  ### Note

  If the mechanism you use to configure a JDBC URL is XML-based, you will need to use the XML character literal &amp; to separate configuration parameters, as the ampersand is a reserved character for XML.

The properties are listed in the following tables.

Connection/Authentication.

Property Name | Definition | Default Value | Since Version
user | The user to connect as |  | all versions
password | The password to use when connecting |  | all versions
socketFactory | The name of the class that the driver should use for creating socket connections to the server. This class must implement the interface 'com.mysql.jdbc.SocketFactory' and have public no-args constructor. | com.mysql.jdbc.StandardSocketFactory | 3.0.3
connectTimeout | Timeout for socket connect (in milliseconds), with 0 being no timeout. Only works on JDK-1.4 or newer. Defaults to '0'. | 0 | 3.0.1
socketTimeout | Timeout on network socket operations (0, the default means no timeout). | 0 | 3.0.1

connectionLifecycleInterceptors

A comma-delimited list of classes that implement "com.mysql.jdbc.ConnectionLifecycleInterceptor" that should notified of connection lifecycle events (creation, destruction, commit, rollback, setCatalog and setAutoCommit) and potentially alter the execution of these commands. ConnectionLifecycleInterceptors are "stackable", more than one interceptor may be specified via the configuration property as a comma-delimited list, with the interceptors executed in order from left to right.

5.1.4

useConfigs | Load the comma-delimited list of configuration properties before parsing the URL or applying user-specified properties. These configurations are explained in the 'Configurations' of the documentation. |  | 3.1.5
interactiveClient | Set the CLIENT_INTERACTIVE flag, which tells MySQL to timeout connections based on INTERACTIVE_TIMEOUT instead of WAIT_TIMEOUT | false | 3.1.0
localSocketAddress | Hostname or IP address given to explicitly configure the interface that the driver will bind the client side of the TCP/IP connection to when connecting. |  | 5.0.5
propertiesTransform | An implementation of com.mysql.jdbc.ConnectionPropertiesTransform that the driver will use to modify URL properties passed to the driver before attempting a connection |  | 3.1.4
useCompression | Use zlib compression when communicating with the server (true/false)? Defaults to 'false'. | false | 3.0.17

Networking.

Property Name | Definition | Default Value | Since Version
tcpKeepAlive | If connecting using TCP/IP, should the driver set SO_KEEPALIVE? | true | 5.0.7
tcpNoDelay | If connecting using TCP/IP, should the driver set SO_TCP_NODELAY (disabling the Nagle Algorithm)? | true | 5.0.7
tcpRcvBuf | If connecting using TCP/IP, should the driver set SO_RCV_BUF to the given value? The default value of '0', means use the platform default value for this property) | 0 | 5.0.7
tcpSndBuf | If connecting using TCP/IP, shuold the driver set SO_SND_BUF to the given value? The default value of '0', means use the platform default value for this property) | 0 | 5.0.7
tcpTrafficClass | If connecting using TCP/IP, should the driver set traffic class or type-of-service fields ?See the documentation for java.net.Socket.setTrafficClass() for more information. | 0 | 5.0.7

High Availability and Clustering.

Property Name | Definition | Default Value | Since Version

autoReconnect

Should the driver try to re-establish stale and/or dead connections? If enabled the driver will throw an exception for a queries issued on a stale or dead connection, which belong to the current transaction, but will attempt reconnect before the next query issued on the connection in a new transaction. The use of this feature is not recommended, because it has side effects related to session state and data consistency when applications don't handle SQLExceptions properly, and is only designed to be used when you are unable to configure your application to handle SQLExceptions resulting from dead and stale connections properly. Alternatively, investigate setting the MySQL server variable "wait_timeout" to some high value rather than the default of 8 hours.

false

1.1

autoReconnectForPools | Use a reconnection strategy appropriate for connection pools (defaults to 'false') | false | 3.1.3
failOverReadOnly | When failing over in autoReconnect mode, should the connection be set to 'read-only'? | true | 3.0.12
maxReconnects | Maximum number of reconnects to attempt if autoReconnect is true, default is '3'. | 3 | 1.1
reconnectAtTxEnd | If autoReconnect is set to true, should the driver attempt reconnections at the end of every transaction? | false | 3.0.10
initialTimeout | If autoReconnect is enabled, the initial time to wait between re-connect attempts (in seconds, defaults to '2'). | 2 | 1.1
roundRobinLoadBalance | When autoReconnect is enabled, and failoverReadonly is false, should we pick hosts to connect to on a round-robin basis? | false | 3.1.2
queriesBeforeRetryMaster | Number of queries to issue before falling back to master when failed over (when using multi-host failover). Whichever condition is met first, 'queriesBeforeRetryMaster' or 'secondsBeforeRetryMaster' will cause an attempt to be made to reconnect to the master. Defaults to 50. | 50 | 3.0.2
secondsBeforeRetryMaster | How long should the driver wait, when failed over, before attempting | 30 | 3.0.2
resourceId | A globally unique name that identifies the resource that this datasource or connection is connected to, used for XAResource.isSameRM() when the driver can't determine this value based on hostnames used in the URL |  | 5.0.1

Security.

Property Name | Definition | Default Value | Since Version
allowMultiQueries | Allow the use of ';' to delimit multiple queries during one statement (true/false), defaults to 'false' | false | 3.1.1
useSSL | Use SSL when communicating with the server (true/false), defaults to 'false' | false | 3.0.2
requireSSL | Require SSL connection if useSSL=true? (defaults to 'false'). | false | 3.1.0
allowLoadLocalInfile | Should the driver allow use of 'LOAD DATA LOCAL INFILE...' (defaults to 'true'). | true | 3.0.3
allowUrlInLocalInfile | Should the driver allow URLs in 'LOAD DATA LOCAL INFILE' statements? | false | 3.1.4
clientCertificateKeyStorePassword | Password for the client certificates KeyStore |  | 5.1.0
clientCertificateKeyStoreType | KeyStore type for client certificates (NULL or empty means use default, standard keystore types supported by the JVM are "JKS" and "PKCS12", your environment may have more available depending on what security products are installed and available to the JVM. |  | 5.1.0
clientCertificateKeyStoreUrl | URL to the client certificate KeyStore (if not specified, use defaults) |  | 5.1.0
trustCertificateKeyStorePassword | Password for the trusted root certificates KeyStore |  | 5.1.0
trustCertificateKeyStoreType | KeyStore type for trusted root certificates (NULL or empty means use default, standard keystore types supported by the JVM are "JKS" and "PKCS12", your environment may have more available depending on what security products are installed and available to the JVM. |  | 5.1.0
trustCertificateKeyStoreUrl | URL to the trusted root certificate KeyStore (if not specified, use defaults) |  | 5.1.0
paranoid | Take measures to prevent exposure sensitive information in error messages and clear data structures holding sensitive data when possible? (defaults to 'false') | false | 3.0.1

Performance Extensions.

Property Name | Definition | Default Value | Since Version
callableStmtCacheSize | If 'cacheCallableStmts' is enabled, how many callable statements should be cached? | 100 | 3.1.2
metadataCacheSize | The number of queries to cache ResultSetMetadata for if cacheResultSetMetaData is set to 'true' (default 50) | 50 | 3.1.1
prepStmtCacheSize | If prepared statement caching is enabled, how many prepared statements should be cached? | 25 | 3.0.10
prepStmtCacheSqlLimit | If prepared statement caching is enabled, what's the largest SQL the driver will cache the parsing for? | 256 | 3.0.10

alwaysSendSetIsolation

Should the driver always communicate with the database when Connection.setTransactionIsolation() is called? If set to false, the driver will only communicate with the database when the requested transaction isolation is different than the whichever is newer, the last value that was set via Connection.setTransactionIsolation(), or the value that was read from the server when the connection was established.

true

3.1.7

maintainTimeStats | Should the driver maintain various internal timers to enable idle time calculations as well as more verbose error messages when the connection to the server fails? Setting this property to false removes at least two calls to System.getCurrentTimeMillis() per query. | true | 3.1.9
useCursorFetch | If connected to MySQL > 5.0.2, and setFetchSize() > 0 on a statement, should that statement use cursor-based fetching to retrieve rows? | false | 5.0.0
blobSendChunkSize | Chunk to use when sending BLOB/CLOBs via ServerPreparedStatements | 1048576 | 3.1.9
cacheCallableStmts | Should the driver cache the parsing stage of CallableStatements | false | 3.1.2
cachePrepStmts | Should the driver cache the parsing stage of PreparedStatements of client-side prepared statements, the "check" for suitability of server-side prepared and server-side prepared statements themselves? | false | 3.0.10
cacheResultSetMetadata | Should the driver cache ResultSetMetaData for Statements and PreparedStatements? (Req. JDK-1.4+, true/false, default 'false') | false | 3.1.1
cacheServerConfiguration | Should the driver cache the results of 'SHOW VARIABLES' and 'SHOW COLLATION' on a per-URL basis? | false | 3.1.5
defaultFetchSize | The driver will call setFetchSize(n) with this value on all newly-created Statements | 0 | 3.1.9
dontTrackOpenResources | The JDBC specification requires the driver to automatically track and close resources, however if your application doesn't do a good job of explicitly calling close() on statements or result sets, this can cause memory leakage. Setting this property to true relaxes this constraint, and can be more memory efficient for some applications. | false | 3.1.7
dynamicCalendars | Should the driver retrieve the default calendar when required, or cache it per connection/session? | false | 3.1.5
elideSetAutoCommits | If using MySQL-4.1 or newer, should the driver only issue 'set autocommit=n' queries when the server's state doesn't match the requested state by Connection.setAutoCommit(boolean)? | false | 3.1.3

enableQueryTimeouts

When enabled, query timeouts set via Statement.setQueryTimeout() use a shared java.util.Timer instance for scheduling. Even if the timeout doesn't expire before the query is processed, there will be memory used by the TimerTask for the given timeout which won't be reclaimed until the time the timeout would have expired if it hadn't been cancelled by the driver. High-load environments might want to consider disabling this functionality.

true

5.0.6

holdResultsOpenOverStatementClose | Should the driver close result sets on Statement.close() as required by the JDBC specification? | false | 3.1.7
largeRowSizeThreshold | What size result set row should the JDBC driver consider "large", and thus use a more memory-efficient way of representing the row internally? | 2048 | 5.1.1

loadBalanceStrategy

If using a load-balanced connection to connect to SQL nodes in a MySQL Cluster/NDB configuration (by using the URL prefix "jdbc:mysql:loadbalance://"), which load balancing algorithm should the driver use: (1) "random" - the driver will pick a random host for each request. This tends to work better than round-robin, as the randomness will somewhat account for spreading loads where requests vary in response time, while round-robin can sometimes lead to overloaded nodes if there are variations in response times across the workload. (2) "bestResponseTime" - the driver will route the request to the host that had the best response time for the previous transaction.

random

5.0.6

locatorFetchBufferSize | If 'emulateLocators' is configured to 'true', what size buffer should be used when fetching BLOB data for getBinaryInputStream? | 1048576 | 3.2.1

rewriteBatchedStatements

Should the driver use multiqueries (irregardless of the setting of "allowMultiQueries") as well as rewriting of prepared statements for INSERT into multi-value inserts when executeBatch() is called? Notice that this has the potential for SQL injection if using plain java.sql.Statements and your code doesn't sanitize input correctly. Notice that for prepared statements, server-side prepared statements can not currently take advantage of this rewrite option, and that if you don't specify stream lengths when using PreparedStatement.set*Stream(), the driver won't be able to determine the optimum number of parameters per batch and you might receive an error from the driver that the resultant packet is too large. Statement.getGeneratedKeys() for these rewritten statements only works when the entire batch includes INSERT statements.

false

3.1.13

useDirectRowUnpack | Use newer result set row unpacking code that skips a copy from network buffers to a MySQL packet instance and instead reads directly into the result set row data buffers. | true | 5.1.1
useDynamicCharsetInfo | Should the driver use a per-connection cache of character set information queried from the server when necessary, or use a built-in static mapping that is more efficient, but isn't aware of custom character sets or character sets implemented after the release of the JDBC driver? | true | 5.0.6
useFastDateParsing | Use internal String->Date/Time/Timestamp conversion routines to avoid excessive object creation? | true | 5.0.5
useFastIntParsing | Use internal String->Integer conversion routines to avoid excessive object creation? | true | 3.1.4
useJvmCharsetConverters | Always use the character encoding routines built into the JVM, rather than using lookup tables for single-byte character sets? | false | 5.0.1
useLocalSessionState | Should the driver refer to the internal values of autocommit and transaction isolation that are set by Connection.setAutoCommit() and Connection.setTransactionIsolation() and transaction state as maintained by the protocol, rather than querying the database or blindly sending commands to the database for commit() or rollback() method calls? | false | 3.1.7
useReadAheadInput | Use newer, optimized non-blocking, buffered input stream when reading from the server? | true | 3.1.5

Debugging/Profiling.

Property Name | Definition | Default Value | Since Version
logger | The name of a class that implements "com.mysql.jdbc.log.Log" that will be used to log messages to. (default is "com.mysql.jdbc.log.StandardLogger", which logs to STDERR) | com.mysql.jdbc.log.StandardLogger | 3.1.1
gatherPerfMetrics | Should the driver gather performance metrics, and report them via the configured logger every 'reportMetricsIntervalMillis' milliseconds? | false | 3.1.2
profileSQL | Trace queries and their execution/fetch times to the configured logger (true/false) defaults to 'false' | false | 3.1.0
profileSql | Deprecated, use 'profileSQL' instead. Trace queries and their execution/fetch times on STDERR (true/false) defaults to 'false' |  | 2.0.14
reportMetricsIntervalMillis | If 'gatherPerfMetrics' is enabled, how often should they be logged (in ms)? | 30000 | 3.1.2
maxQuerySizeToLog | Controls the maximum length/size of a query that will get logged when profiling or tracing | 2048 | 3.1.3
packetDebugBufferSize | The maximum number of packets to retain when 'enablePacketDebug' is true | 20 | 3.1.3
slowQueryThresholdMillis | If 'logSlowQueries' is enabled, how long should a query (in ms) before it is logged as 'slow'? | 2000 | 3.1.2
slowQueryThresholdNanos | If 'useNanosForElapsedTime' is set to true, and this property is set to a non-zero value, the driver will use this threshold (in nanosecond units) to determine if a query was slow. | 0 | 5.0.7
useUsageAdvisor | Should the driver issue 'usage' warnings advising proper and efficient usage of JDBC and MySQL Connector/J to the log (true/false, defaults to 'false')? | false | 3.1.1
autoGenerateTestcaseScript | Should the driver dump the SQL it is executing, including server-side prepared statements to STDERR? | false | 3.1.9
autoSlowLog | Instead of using slowQueryThreshold* to determine if a query is slow enough to be logged, maintain statistics that allow the driver to determine queries that are outside the 99th percentile? | true | 5.1.4
clientInfoProvider | The name of a class that implements the com.mysql.jdbc.JDBC4ClientInfoProvider interface in order to support JDBC-4.0's Connection.get/setClientInfo() methods | com.mysql.jdbc.JDBC4CommentClientInfoProvider | 5.1.0
dumpMetadataOnColumnNotFound | Should the driver dump the field-level metadata of a result set into the exception message when ResultSet.findColumn() fails? | false | 3.1.13
dumpQueriesOnException | Should the driver dump the contents of the query sent to the server in the message for SQLExceptions? | false | 3.1.3
enablePacketDebug | When enabled, a ring-buffer of 'packetDebugBufferSize' packets will be kept, and dumped when exceptions are thrown in key areas in the driver's code | false | 3.1.3
explainSlowQueries | If 'logSlowQueries' is enabled, should the driver automatically issue an 'EXPLAIN' on the server and send the results to the configured log at a WARN level? | false | 3.1.2
includeInnodbStatusInDeadlockExceptions | Include the output of "SHOW ENGINE INNODB STATUS" in exception messages when deadlock exceptions are detected? | false | 5.0.7
logSlowQueries | Should queries that take longer than 'slowQueryThresholdMillis' be logged? | false | 3.1.2
logXaCommands | Should the driver log XA commands sent by MysqlXaConnection to the server, at the DEBUG level of logging? | false | 5.0.5
resultSetSizeThreshold | If the usage advisor is enabled, how many rows should a result set contain before the driver warns that it is suspiciously large? | 100 | 5.0.5
traceProtocol | Should trace-level network protocol be logged? | false | 3.1.2
useNanosForElapsedTime | For profiling/debugging functionality that measures elapsed time, should the driver try to use nanoseconds resolution if available (JDK >= 1.5)? | false | 5.0.7

Miscellaneous.

Property Name | Definition | Default Value | Since Version
useUnicode | Should the driver use Unicode character encodings when handling strings? Should only be used when the driver can't determine the character set mapping, or you are trying to 'force' the driver to use a character set that MySQL either doesn't natively support (such as UTF-8), true/false, defaults to 'true' | true | 1.1g
characterEncoding | If 'useUnicode' is set to true, what character encoding should the driver use when dealing with strings? (defaults is to 'autodetect') |  | 1.1g
characterSetResults | Character set to tell the server to return results as. |  | 3.0.13
connectionCollation | If set, tells the server to use this collation via 'set collation_connection' |  | 3.0.13
useBlobToStoreUTF8OutsideBMP | Tells the driver to treat [MEDIUM/LONG]BLOB columns as [LONG]VARCHAR columns holding text encoded in UTF-8 that has characters outside the BMP (4-byte encodings), which MySQL server can't handle natively. | false | 5.1.3
utf8OutsideBmpExcludedColumnNamePattern | When "useBlobToStoreUTF8OutsideBMP" is set to "true", column names matching the given regex will still be treated as BLOBs unless they match the regex specified for "utf8OutsideBmpIncludedColumnNamePattern". The regex must follow the patterns used for the java.util.regex package. |  | 5.1.3
utf8OutsideBmpIncludedColumnNamePattern | Used to specify exclusion rules to "utf8OutsideBmpExcludedColumnNamePattern". The regex must follow the patterns used for the java.util.regex package. |  | 5.1.3
sessionVariables | A comma-separated list of name/value pairs to be sent as SET SESSION ... to the server when the driver connects. |  | 3.1.8
allowNanAndInf | Should the driver allow NaN or +/- INF values in PreparedStatement.setDouble()? | false | 3.1.5
autoClosePStmtStreams | Should the driver automatically call .close() on streams/readers passed as arguments via set*() methods? | false | 3.1.12
autoDeserialize | Should the driver automatically detect and de-serialize objects stored in BLOB fields? | false | 3.1.5
blobsAreStrings | Should the driver always treat BLOBs as Strings - specifically to work around dubious metadata returned by the server for GROUP BY clauses? | false | 5.0.8
capitalizeTypeNames | Capitalize type names in DatabaseMetaData? (usually only useful when using WebObjects, true/false, defaults to 'false') | true | 2.0.7
clobCharacterEncoding | The character encoding to use for sending and retrieving TEXT, MEDIUMTEXT and LONGTEXT values instead of the configured connection characterEncoding |  | 5.0.0
clobberStreamingResults | This will cause a 'streaming' ResultSet to be automatically closed, and any outstanding data still streaming from the server to be discarded if another query is executed before all the data has been read from the server. | false | 3.0.9
continueBatchOnError | Should the driver continue processing batch commands if one statement fails. The JDBC spec allows either way (defaults to 'true'). | true | 3.0.3
createDatabaseIfNotExist | Creates the database given in the URL if it doesn't yet exist. Assumes the configured user has permissions to create databases. | false | 3.1.9
emptyStringsConvertToZero | Should the driver allow conversions from empty string fields to numeric values of '0'? | true | 3.1.8

emulateLocators

Should the driver emulate java.sql.Blobs with locators? With this feature enabled, the driver will delay loading the actual Blob data until the one of the retrieval methods (getInputStream(), getBytes(), and so forth) on the blob data stream has been accessed. For this to work, you must use a column alias with the value of the column to the actual name of the Blob. The feature also has the following restrictions: The SELECT that created the result set must reference only one table, the table must have a primary key; the SELECT must alias the original blob column name, specified as a string, to an alternate name; the SELECT must cover all columns that make up the primary key.

false

3.1.0

emulateUnsupportedPstmts | Should the driver detect prepared statements that are not supported by the server, and replace them with client-side emulated versions? | true | 3.1.7
functionsNeverReturnBlobs | Should the driver always treat data from functions returning BLOBs as Strings - specifically to work around dubious metadata returned by the server for GROUP BY clauses? | false | 5.0.8
generateSimpleParameterMetadata | Should the driver generate simplified parameter metadata for PreparedStatements when no metadata is available either because the server couldn't support preparing the statement, or server-side prepared statements are disabled? | false | 5.0.5
ignoreNonTxTables | Ignore non-transactional table warning for rollback? (defaults to 'false'). | false | 3.0.9
jdbcCompliantTruncation | Should the driver throw java.sql.DataTruncation exceptions when data is truncated as is required by the JDBC specification when connected to a server that supports warnings (MySQL 4.1.0 and newer)? This property has no effect if the server sql-mode includes STRICT_TRANS_TABLES. | true | 3.1.2
maxRows | The maximum number of rows to return (0, the default means return all rows). | -1 | all versions
netTimeoutForStreamingResults | What value should the driver automatically set the server setting 'net_write_timeout' to when the streaming result sets feature is in use? (value has unit of seconds, the value '0' means the driver will not try and adjust this value) | 600 | 5.1.0

noAccessToProcedureBodies

When determining procedure parameter types for CallableStatements, and the connected user can't access procedure bodies through "SHOW CREATE PROCEDURE" or select on mysql.proc should the driver instead create basic metadata (all parameters reported as IN VARCHARs, but allowing registerOutParameter() to be called on them anyway) instead of throwing an exception?

false

5.0.3

noDatetimeStringSync | Don't ensure that ResultSet.getDatetimeType().toString().equals(ResultSet.getString()) | false | 3.1.7
noTimezoneConversionForTimeType | Don't convert TIME values using the server timezone if 'useTimezone'='true' | false | 5.0.0
nullCatalogMeansCurrent | When DatabaseMetadataMethods ask for a 'catalog' parameter, does the value null mean use the current catalog? (this is not JDBC-compliant, but follows legacy behavior from earlier versions of the driver) | true | 3.1.8
nullNamePatternMatchesAll | Should DatabaseMetaData methods that accept *pattern parameters treat null the same as '%' (this is not JDBC-compliant, however older versions of the driver accepted this departure from the specification) | true | 3.1.8

overrideSupportsIntegrityEnhancementFacility

Should the driver return "true" for DatabaseMetaData.supportsIntegrityEnhancementFacility() even if the database doesn't support it to workaround applications that require this method to return "true" to signal support of foreign keys, even though the SQL specification states that this facility contains much more than just foreign key support (one such application being OpenOffice)?

false

3.1.12

padCharsWithSpace | If a result set column has the CHAR type and the value does not fill the amount of characters specified in the DDL for the column, should the driver pad the remaining characters with space (for ANSI compliance)? | false | 5.0.6
pedantic | Follow the JDBC spec to the letter. | false | 3.0.0
pinGlobalTxToPhysicalConnection | When using XAConnections, should the driver ensure that operations on a given XID are always routed to the same physical connection? This allows the XAConnection to support "XA START ... JOIN" after "XA END" has been called | false | 5.0.1

populateInsertRowWithDefaultValues

When using ResultSets that are CONCUR_UPDATABLE, should the driver pre-populate the "insert" row with default values from the DDL for the table used in the query so those values are immediately available for ResultSet accessors? This functionality requires a call to the database for metadata each time a result set of this type is created. If disabled (the default), the default values will be populated by the an internal call to refreshRow() which pulls back default values and/or values changed by triggers.

false

5.0.5

processEscapeCodesForPrepStmts | Should the driver process escape codes in queries that are prepared? | true | 3.1.12
relaxAutoCommit | If the version of MySQL the driver connects to does not support transactions, still allow calls to commit(), rollback() and setAutoCommit() (true/false, defaults to 'false')? | false | 2.0.13
retainStatementAfterResultSetClose | Should the driver retain the Statement reference in a ResultSet after ResultSet.close() has been called. This is not JDBC-compliant after JDBC-4.0. | false | 3.1.11
rollbackOnPooledClose | Should the driver issue a rollback() when the logical connection in a pool is closed? | true | 3.0.15
runningCTS13 | Enables workarounds for bugs in Sun's JDBC compliance testsuite version 1.3 | false | 3.1.7
serverTimezone | Override detection/mapping of timezone. Used when timezone from server doesn't map to Java timezone |  | 3.0.2
statementInterceptors | A comma-delimited list of classes that implement "com.mysql.jdbc.StatementInterceptor" that should be placed "in between" query execution to influence the results. StatementInterceptors are "chainable", the results returned by the "current" interceptor will be passed on to the next in in the chain, from left-to-right order, as specified in this property. |  | 5.1.1
strictFloatingPoint | Used only in older versions of compliance test | false | 3.0.0
strictUpdates | Should the driver do strict checking (all primary keys selected) of updatable result sets (true, false, defaults to 'true')? | true | 3.0.4
tinyInt1isBit | Should the driver treat the datatype TINYINT(1) as the BIT type (because the server silently converts BIT -> TINYINT(1) when creating tables)? | true | 3.0.16
transformedBitIsBoolean | If the driver converts TINYINT(1) to a different type, should it use BOOLEAN instead of BIT for future compatibility with MySQL-5.0, as MySQL-5.0 has a BIT type? | false | 3.1.9
treatUtilDateAsTimestamp | Should the driver treat java.util.Date as a TIMESTAMP for the purposes of PreparedStatement.setObject()? | true | 5.0.5
ultraDevHack | Create PreparedStatements for prepareCall() when required, because UltraDev is broken and issues a prepareCall() for _all_ statements? (true/false, defaults to 'false') | false | 2.0.3
useGmtMillisForDatetimes | Convert between session timezone and GMT before creating Date and Timestamp instances (value of "false" is legacy behavior, "true" leads to more JDBC-compliant behavior. | false | 3.1.12
useHostsInPrivileges | Add '@hostname' to users in DatabaseMetaData.getColumn/TablePrivileges() (true/false), defaults to 'true'. | true | 3.0.2
useInformationSchema | When connected to MySQL-5.0.7 or newer, should the driver use the INFORMATION_SCHEMA to derive information used by DatabaseMetaData? | false | 5.0.0
useJDBCCompliantTimezoneShift | Should the driver use JDBC-compliant rules when converting TIME/TIMESTAMP/DATETIME values' timezone information for those JDBC arguments which take a java.util.Calendar argument? (Notice that this option is exclusive of the "useTimezone=true" configuration option.) | false | 5.0.0
useOldAliasMetadataBehavior | Should the driver use the legacy behavior for "AS" clauses on columns and tables, and only return aliases (if any) for ResultSetMetaData.getColumnName() or ResultSetMetaData.getTableName() rather than the original column/table name? | false | 5.0.4
useOldUTF8Behavior | Use the UTF-8 behavior the driver did when communicating with 4.0 and older servers | false | 3.1.6
useOnlyServerErrorMessages | Don't prepend 'standard' SQLState error messages to error messages returned by the server. | true | 3.0.15
useSSPSCompatibleTimezoneShift | If migrating from an environment that was using server-side prepared statements, and the configuration property "useJDBCCompliantTimeZoneShift" set to "true", use compatible behavior when not using server-side prepared statements when sending TIMESTAMP values to the MySQL server. | false | 5.0.5
useServerPrepStmts | Use server-side prepared statements if the server supports them? | false | 3.1.0
useSqlStateCodes | Use SQL Standard state codes instead of 'legacy' X/Open/SQL state codes (true/false), default is 'true' | true | 3.1.3
useStreamLengthsInPrepStmts | Honor stream length parameter in PreparedStatement/ResultSet.setXXXStream() method calls (true/false, defaults to 'true')? | true | 3.0.2
useTimezone | Convert time/date types between client and server timezones (true/false, defaults to 'false')? | false | 3.0.2
useUnbufferedInput | Don't use BufferedInputStream for reading data from the server | true | 3.0.11
yearIsDateType | Should the JDBC driver treat the MySQL type "YEAR" as a java.sql.Date, or as a SHORT? | true | 3.1.9
zeroDateTimeBehavior | What should happen when the driver encounters DATETIME values that are composed entirely of zeroes (used by MySQL to represent invalid dates)? Valid values are "exception", "round" and "convertToNull". | exception | 3.1.4

Connector/J also supports access to MySQL via named pipes on Windows NT/2000/XP using the NamedPipeSocketFactory as a plugin-socket factory via the socketFactory property. If you don't use a namedPipePath property, the default of '\\.\pipe\MySQL' will be used. If you use the `NamedPipeSocketFactory`, the hostname and port number values in the JDBC url will be ignored. You can enable this feature using:

    socketFactory=com.mysql.jdbc.NamedPipeSocketFactory

Named pipes only work when connecting to a MySQL server on the same physical machine as the one the JDBC driver is being used on. In simple performance tests, it appears that named pipe access is between 30%-50% faster than the standard TCP/IP access.

You can create your own socket factories by following the example code in `com.mysql.jdbc.NamedPipeSocketFactory`, or `com.mysql.jdbc.StandardSocketFactory`.

#### 1.4.2. JDBC API Implementation Notes

MySQL Connector/J passes all of the tests in the publicly-available version of Sun's JDBC compliance test suite. However, in many places the JDBC specification is vague about how certain functionality should be implemented, or the specification allows leeway in implementation.

This section gives details on a interface-by-interface level about how certain implementation decisions may affect how you use MySQL Connector/J.

- Blob

  Starting with Connector/J version 3.1.0, you can emulate Blobs with locators by adding the property 'emulateLocators=true' to your JDBC URL. Using this method, the driver will delay loading the actual Blob data until you retrieve the other data and then use retrieval methods (`getInputStream()`, `getBytes()`, and so forth) on the blob data stream.

  For this to work, you must use a column alias with the value of the column to the actual name of the Blob, for example:

      SELECT id, 'data' as blob_data from blobtable

  For this to work, you must also follow follow these rules:

  - The `SELECT` must also reference only one table, the table must have a primary key.

  - The `SELECT` must alias the original blob column name, specified as a string, to an alternate name.

  - The `SELECT` must cover all columns that make up the primary key.

  The Blob implementation does not allow in-place modification (they are copies, as reported by the `DatabaseMetaData.locatorsUpdateCopies()` method). Because of this, you should use the corresponding `PreparedStatement.setBlob()` or `ResultSet.updateBlob()` (in the case of updatable result sets) methods to save changes back to the database.

  MySQL Enterprise MySQL Enterprise subscribers will find more information about type conversion in the Knowledge Base article, Type Conversions Supported by MySQL Connector/J. To subscribe to MySQL Enterprise see http://www.mysql.com/products/enterprise/advisors.html.

- CallableStatement

  Starting with Connector/J 3.1.1, stored procedures are supported when connecting to MySQL version 5.0 or newer via the `CallableStatement` interface. Currently, the `getParameterMetaData()` method of `CallableStatement` is not supported.

- Clob

  The Clob implementation does not allow in-place modification (they are copies, as reported by the `DatabaseMetaData.locatorsUpdateCopies()` method). Because of this, you should use the `PreparedStatement.setClob()` method to save changes back to the database. The JDBC API does not have a `ResultSet.updateClob()` method.

- Connection

  Unlike older versions of MM.MySQL the `isClosed()` method does not ping the server to determine if it is alive. In accordance with the JDBC specification, it only returns true if `closed()` has been called on the connection. If you need to determine if the connection is still valid, you should issue a simple query, such as `SELECT 1`. The driver will throw an exception if the connection is no longer valid.

- DatabaseMetaData

  Foreign Key information (`getImportedKeys()`/`getExportedKeys()` and `getCrossReference()`) is only available from InnoDB tables. However, the driver uses `SHOW CREATE TABLE` to retrieve this information, so when other storage engines support foreign keys, the driver will transparently support them as well.

- PreparedStatement

  PreparedStatements are implemented by the driver, as MySQL does not have a prepared statement feature. Because of this, the driver does not implement `getParameterMetaData()` or `getMetaData()` as it would require the driver to have a complete SQL parser in the client.

  Starting with version 3.1.0 MySQL Connector/J, server-side prepared statements and binary-encoded result sets are used when the server supports them.

  Take care when using a server-side prepared statement with large parameters that are set via `setBinaryStream()`, `setAsciiStream()`, `setUnicodeStream()`, `setBlob()`, or `setClob()`. If you want to re-execute the statement with any large parameter changed to a non-large parameter, it is necessary to call `clearParameters()` and set all parameters again. The reason for this is as follows:

  - During both server-side prepared statements and client-side emulation, large data is exchanged only when `PreparedStatement.execute()` is called.

  - Once that has been done, the stream used to read the data on the client side is closed (as per the JDBC spec), and can't be read from again.

  - If a parameter changes from large to non-large, the driver must reset the server-side state of the prepared statement to allow the parameter that is being changed to take the place of the prior large value. This removes all of the large data that has already been sent to the server, thus requiring the data to be re-sent, via the `setBinaryStream()`, `setAsciiStream()`, `setUnicodeStream()`, `setBlob()` or `setClob()` methods.

  Consequently, if you want to change the type of a parameter to a non-large one, you must call `clearParameters()` and set all parameters of the prepared statement again before it can be re-executed.

- ResultSet

  By default, ResultSets are completely retrieved and stored in memory. In most cases this is the most efficient way to operate, and due to the design of the MySQL network protocol is easier to implement. If you are working with ResultSets that have a large number of rows or large values, and can not allocate heap space in your JVM for the memory required, you can tell the driver to stream the results back one row at a time.

  To enable this functionality, you need to create a Statement instance in the following manner:

      stmt = conn.createStatement(java.sql.ResultSet.TYPE_FORWARD_ONLY,
                    java.sql.ResultSet.CONCUR_READ_ONLY);
      stmt.setFetchSize(Integer.MIN_VALUE);

  The combination of a forward-only, read-only result set, with a fetch size of `Integer.MIN_VALUE` serves as a signal to the driver to stream result sets row-by-row. After this any result sets created with the statement will be retrieved row-by-row.

  There are some caveats with this approach. You will have to read all of the rows in the result set (or close it) before you can issue any other queries on the connection, or an exception will be thrown.

  The earliest the locks these statements hold can be released (whether they be `MyISAM` table-level locks or row-level locks in some other storage engine such as `InnoDB`) is when the statement completes.

  If the statement is within scope of a transaction, then locks are released when the transaction completes (which implies that the statement needs to complete first). As with most other databases, statements are not complete until all the results pending on the statement are read or the active result set for the statement is closed.

  Therefore, if using streaming results, you should process them as quickly as possible if you want to maintain concurrent access to the tables referenced by the statement producing the result set.

- ResultSetMetaData

  The `isAutoIncrement()` method only works when using MySQL servers 4.0 and newer.

- Statement

  When using versions of the JDBC driver earlier than 3.2.1, and connected to server versions earlier than 5.0.3, the `setFetchSize()` method has no effect, other than to toggle result set streaming as described above.

  Connector/J 5.0.0 and later include support for both `Statement.cancel()` and `Statement.setQueryTimeout()`. Both require MySQL 5.0.0 or newer server, and require a separate connection to issue the `KILL QUERY` statement. In the case of `setQueryTimeout()`, the implementation creates an additional thread to handle the timeout functionality.

  ### Note

  Failures to cancel the statement for `setQueryTimeout()` may manifest themselves as `RuntimeException` rather than failing silently, as there is currently no way to unblock the thread that is executing the query being cancelled due to timeout expiration and have it throw the exception instead.

  MySQL does not support SQL cursors, and the JDBC driver doesn't emulate them, so "setCursorName()" has no effect.

  Connector/J 5.1.3 and later include two additional methods:

  - `setLocalInfileInputStream()` sets an `InputStream` instance that will be used to send data to the MySQL server for a `LOAD DATA LOCAL INFILE` statement rather than a `FileInputStream` or `URLInputStream` that represents the path given as an argument to the statement.

    This stream will be read to completion upon execution of a `LOAD DATA LOCAL INFILE` statement, and will automatically be closed by the driver, so it needs to be reset before each call to `execute*()` that would cause the MySQL server to request data to fulfill the request for `LOAD DATA LOCAL INFILE`.

    If this value is set to `NULL`, the driver will revert to using a `FileInputStream` or `URLInputStream` as required.

  - `getLocalInfileInputStream()` returns the `InputStream` instance that will be used to send data in response to a `LOAD DATA LOCAL INFILE` statement.

    This method returns `NULL` if no such stream has been set via `setLocalInfileInputStream()`.

#### 1.4.3. Java, JDBC and MySQL Types

MySQL Connector/J is flexible in the way it handles conversions between MySQL data types and Java data types.

In general, any MySQL data type can be converted to a java.lang.String, and any numerical type can be converted to any of the Java numerical types, although round-off, overflow, or loss of precision may occur.

Starting with Connector/J 3.1.0, the JDBC driver will issue warnings or throw DataTruncation exceptions as is required by the JDBC specification unless the connection was configured not to do so by using the property jdbcCompliantTruncation and setting it to `false`.

The conversions that are always guaranteed to work are listed in the following table:

Connection Properties - Miscellaneous.

These MySQL Data Types | Can always be converted to these Java types
`CHAR, VARCHAR, BLOB, TEXT, ENUM, and SET` | `java.lang.String, java.io.InputStream, java.io.Reader, java.sql.Blob, java.sql.Clob`
`FLOAT, REAL, DOUBLE PRECISION, NUMERIC, DECIMAL, TINYINT, SMALLINT, MEDIUMINT, INTEGER, BIGINT` | `java.lang.String, java.lang.Short, java.lang.Integer, java.lang.Long, java.lang.Double, java.math.BigDecimal`
`DATE, TIME, DATETIME, TIMESTAMP` | `java.lang.String, java.sql.Date, java.sql.Timestamp`

### Note

Round-off, overflow or loss of precision may occur if you choose a Java numeric data type that has less precision or capacity than the MySQL data type you are converting to/from.

The `ResultSet.getObject()` method uses the type conversions between MySQL and Java types, following the JDBC specification where appropriate. The value returned by `ResultSetMetaData.GetColumnClassName()` is also shown below. For more information on the `java.sql.Types` classes see Java 2 Platform Types.

MySQL Types to Java Types for ResultSet.getObject().

MySQL Type Name | Return value of `GetColumnClassName` | Returned as Java Class
BIT(1) (new in MySQL-5.0) | BIT | `java.lang.Boolean`
BIT( > 1) (new in MySQL-5.0) | BIT | `byte[]`
TINYINT | TINYINT | `java.lang.Boolean` if the configuration property `tinyInt1isBit` is set to `true` (the default) and the storage size is 1, or `java.lang.Integer` if not.
BOOL, BOOLEAN | TINYINT | See TINYINT, above as these are aliases for TINYINT(1), currently.
SMALLINT[(M)] [UNSIGNED] | SMALLINT [UNSIGNED] | `java.lang.Integer` (regardless if UNSIGNED or not)
MEDIUMINT[(M)] [UNSIGNED] | MEDIUMINT [UNSIGNED] | `java.lang.Integer,` if UNSIGNED `java.lang.Long`
INT,INTEGER[(M)] [UNSIGNED] | INTEGER [UNSIGNED] | `java.lang.Integer`, if UNSIGNED `java.lang.Long`
BIGINT[(M)] [UNSIGNED] | BIGINT [UNSIGNED] | `java.lang.Long`, if UNSIGNED `java.math.BigInteger`
FLOAT[(M,D)] | FLOAT | `java.lang.Float`
DOUBLE[(M,B)] | DOUBLE | `java.lang.Double`
DECIMAL[(M[,D])] | DECIMAL | `java.math.BigDecimal`
DATE | DATE | `java.sql.Date`
DATETIME | DATETIME | `java.sql.Timestamp`
TIMESTAMP[(M)] | TIMESTAMP | `java.sql.Timestamp`
TIME | TIME | `java.sql.Time`
YEAR[(2|4)] | YEAR | If `yearIsDateType` configuration property is set to false, then the returned object type is `java.sql.Short`. If set to true (the default) then an object of type `java.sql.Date` (with the date set to January 1st, at midnight).
CHAR(M) | CHAR | `java.lang.String` (unless the character set for the column is BINARY, then `byte[]` is returned.
VARCHAR(M) [BINARY] | VARCHAR | `java.lang.String` (unless the character set for the column is BINARY, then `byte[]` is returned.
BINARY(M) | BINARY | `byte[]`
VARBINARY(M) | VARBINARY | `byte[]`
TINYBLOB | TINYBLOB | `byte[]`
TINYTEXT | VARCHAR | `java.lang.String`
BLOB | BLOB | `byte[]`
TEXT | VARCHAR | `java.lang.String`
MEDIUMBLOB | MEDIUMBLOB | `byte[]`
MEDIUMTEXT | VARCHAR | `java.lang.String`
LONGBLOB | LONGBLOB | `byte[]`
LONGTEXT | VARCHAR | `java.lang.String`
ENUM('value1','value2',...) | CHAR | `java.lang.String`
SET('value1','value2',...) | CHAR | `java.lang.String`

#### 1.4.4. Using Character Sets and Unicode

All strings sent from the JDBC driver to the server are converted automatically from native Java Unicode form to the client character encoding, including all queries sent via `Statement.execute()`, `Statement.executeUpdate()`, `Statement.executeQuery()` as well as all `PreparedStatement` and `CallableStatement` parameters with the exclusion of parameters set using `setBytes()`, `setBinaryStream()`, `setAsciiStream()`, `setUnicodeStream()` and `setBlob()` .

Prior to MySQL Server 4.1, Connector/J supported a single character encoding per connection, which could either be automatically detected from the server configuration, or could be configured by the user through the `useUnicode` and `characterEncoding` properties.

Starting with MySQL Server 4.1, Connector/J supports a single character encoding between client and server, and any number of character encodings for data returned by the server to the client in `ResultSets`.

The character encoding between client and server is automatically detected upon connection. The encoding used by the driver is specified on the server via the `character_set` system variable for server versions older than 4.1.0 and `character_set_server` for server versions 4.1.0 and newer. For more information, see Server Character Set and Collation.

To override the automatically-detected encoding on the client side, use the `characterEncoding` property in the URL used to connect to the server.

When specifying character encodings on the client side, Java-style names should be used. The following table lists Java-style names for MySQL character sets:

MySQL to Java Encoding Name Translations.

MySQL Character Set Name | Java-Style Character Encoding Name
ascii | US-ASCII
big5 | Big5
gbk | GBK
sjis | SJIS (or Cp932 or MS932 for MySQL Server < 4.1.11)
cp932 | Cp932 or MS932 (MySQL Server > 4.1.11)
gb2312 | EUC_CN
ujis | EUC_JP
euckr | EUC_KR
latin1 | ISO8859_1
latin2 | ISO8859_2
greek | ISO8859_7
hebrew | ISO8859_8
cp866 | Cp866
tis620 | TIS620
cp1250 | Cp1250
cp1251 | Cp1251
cp1257 | Cp1257
macroman | MacRoman
macce | MacCentralEurope
utf8 | UTF-8
ucs2 | UnicodeBig

### Warning

Do not issue the query 'set names' with Connector/J, as the driver will not detect that the character set has changed, and will continue to use the character set detected during the initial connection setup.

To allow multiple character sets to be sent from the client, the UTF-8 encoding should be used, either by configuring `utf8` as the default server character set, or by configuring the JDBC driver to use UTF-8 through the `characterEncoding` property.

#### 1.4.5. Connecting Securely Using SSL

SSL in MySQL Connector/J encrypts all data (other than the initial handshake) between the JDBC driver and the server. The performance penalty for enabling SSL is an increase in query processing time between 35% and 50%, depending on the size of the query, and the amount of data it returns.

For SSL Support to work, you must have the following:

- A JDK that includes JSSE (Java Secure Sockets Extension), like JDK-1.4.1 or newer. SSL does not currently work with a JDK that you can add JSSE to, like JDK-1.2.x or JDK-1.3.x due to the following JSSE bug: http://developer.java.sun.com/developer/bugParade/bugs/4273544.html

- A MySQL server that supports SSL and has been compiled and configured to do so, which is MySQL-4.0.4 or later, see Using Secure Connections, for more information.

- A client certificate (covered later in this section)

You will first need to import the MySQL server CA Certificate into a Java truststore. A sample MySQL server CA Certificate is located in the `SSL` subdirectory of the MySQL source distribution. This is what SSL will use to determine if you are communicating with a secure MySQL server.

To use Java's keytool to create a truststore in the current directory , and import the server's CA certificate (`cacert.pem`), you can do the following (assuming that keytool is in your path. The keytool should be located in the `bin` subdirectory of your JDK or JRE):

    shell> keytool -import -alias mysqlServerCACert \
                                      -file cacert.pem -keystore truststore

Keytool will respond with the following information:

    Enter keystore password:  *********
    Owner: EMAILADDRESS=walrus@example.com, CN=Walrus,
           O=MySQL AB, L=Orenburg, ST=Some-State, C=RU
    Issuer: EMAILADDRESS=walrus@example.com, CN=Walrus,
           O=MySQL AB, L=Orenburg, ST=Some-State, C=RU
    Serial number: 0
    Valid from:
       Fri Aug 02 16:55:53 CDT 2002 until: Sat Aug 02 16:55:53 CDT 2003
    Certificate fingerprints:
        MD5:  61:91:A0:F2:03:07:61:7A:81:38:66:DA:19:C4:8D:AB
        SHA1: 25:77:41:05:D5:AD:99:8C:14:8C:CA:68:9C:2F:B8:89:C3:34:4D:6C
    Trust this certificate? [no]:  yes
    Certificate was added to keystore

You will then need to generate a client certificate, so that the MySQL server knows that it is talking to a secure client:

     shell> keytool -genkey -keyalg rsa \
         -alias mysqlClientCertificate -keystore keystore

Keytool will prompt you for the following information, and create a keystore named `keystore` in the current directory.

You should respond with information that is appropriate for your situation:

    Enter keystore password:  *********
    What is your first and last name?
      [Unknown]:  Matthews
    What is the name of your organizational unit?
      [Unknown]:  Software Development
    What is the name of your organization?
      [Unknown]:  MySQL AB
    What is the name of your City or Locality?
      [Unknown]:  Flossmoor
    What is the name of your State or Province?
      [Unknown]:  IL
    What is the two-letter country code for this unit?
      [Unknown]:  US
    Is <CN=Matthews, OU=Software Development, O=MySQL AB,
     L=Flossmoor, ST=IL, C=US> correct?
      [no]:  y

    Enter key password for <mysqlClientCertificate>
            (RETURN if same as keystore password):

Finally, to get JSSE to use the keystore and truststore that you have generated, you need to set the following system properties when you start your JVM, replacing path_to_keystore_file with the full path to the keystore file you created, path_to_truststore_file with the path to the truststore file you created, and using the appropriate password values for each property. You can do this either on the command line:

    -Djavax.net.ssl.keyStore=path_to_keystore_file
    -Djavax.net.ssl.keyStorePassword=password
    -Djavax.net.ssl.trustStore=path_to_truststore_file
    -Djavax.net.ssl.trustStorePassword=password

Or you can set the values directly within the application:

     System.setProperty("javax.net.ssl.keyStore","path_to_keystore_file");
    System.setProperty("javax.net.ssl.keyStorePassword","password");
    System.setProperty("javax.net.ssl.trustStore","path_to_truststore_file");
    System.setProperty("javax.net.ssl.trustStorePassword","password");

You will also need to set useSSL to `true` in your connection parameters for MySQL Connector/J, either by adding `useSSL=true` to your URL, or by setting the property useSSL to `true` in the `java.util.Properties` instance you pass to `DriverManager.getConnection()`.

You can test that SSL is working by turning on JSSE debugging (as detailed below), and look for the following key events:

    ...
    *** ClientHello, v3.1
    RandomCookie:  GMT: 1018531834 bytes = { 199, 148, 180, 215, 74, 12, »
      54, 244, 0, 168, 55, 103, 215, 64, 16, 138, 225, 190, 132, 153, 2, »
      217, 219, 239, 202, 19, 121, 78 }
    Session ID:  {}
    Cipher Suites:  { 0, 5, 0, 4, 0, 9, 0, 10, 0, 18, 0, 19, 0, 3, 0, 17 }
    Compression Methods:  { 0 }
    ***
    [write] MD5 and SHA1 hashes:  len = 59
    0000: 01 00 00 37 03 01 3D B6 90 FA C7 94 B4 D7 4A 0C  ...7..=.......J.
    0010: 36 F4 00 A8 37 67 D7 40 10 8A E1 BE 84 99 02 D9  6...7g.@........
    0020: DB EF CA 13 79 4E 00 00 10 00 05 00 04 00 09 00  ....yN..........
    0030: 0A 00 12 00 13 00 03 00 11 01 00                 ...........
    main, WRITE:  SSL v3.1 Handshake, length = 59
    main, READ:  SSL v3.1 Handshake, length = 74
    *** ServerHello, v3.1
    RandomCookie:  GMT: 1018577560 bytes = { 116, 50, 4, 103, 25, 100, 58, »
       202, 79, 185, 178, 100, 215, 66, 254, 21, 83, 187, 190, 42, 170, 3, »
       132, 110, 82, 148, 160, 92 }
    Session ID:  {163, 227, 84, 53, 81, 127, 252, 254, 178, 179, 68, 63, »
       182, 158, 30, 11, 150, 79, 170, 76, 255, 92, 15, 226, 24, 17, 177, »
       219, 158, 177, 187, 143}
    Cipher Suite:  { 0, 5 }
    Compression Method: 0
    ***
    %% Created:  [Session-1, SSL_RSA_WITH_RC4_128_SHA]
    ** SSL_RSA_WITH_RC4_128_SHA
    [read] MD5 and SHA1 hashes:  len = 74
    0000: 02 00 00 46 03 01 3D B6 43 98 74 32 04 67 19 64  ...F..=.C.t2.g.d
    0010: 3A CA 4F B9 B2 64 D7 42 FE 15 53 BB BE 2A AA 03  :.O..d.B..S..*..
    0020: 84 6E 52 94 A0 5C 20 A3 E3 54 35 51 7F FC FE B2  .nR..\ ..T5Q....
    0030: B3 44 3F B6 9E 1E 0B 96 4F AA 4C FF 5C 0F E2 18  .D?.....O.L.\...
    0040: 11 B1 DB 9E B1 BB 8F 00 05 00                    ..........
    main, READ:  SSL v3.1 Handshake, length = 1712
    ...

JSSE provides debugging (to STDOUT) when you set the following system property: `-Djavax.net.debug=all` This will tell you what keystores and truststores are being used, as well as what is going on during the SSL handshake and certificate exchange. It will be helpful when trying to determine what is not working when trying to get an SSL connection to happen.

#### 1.4.6. Using Master/Slave Replication with ReplicationConnection

Starting with Connector/J 3.1.7, we've made available a variant of the driver that will automatically send queries to a read/write master, or a failover or round-robin loadbalanced set of slaves based on the state of `Connection.getReadOnly()` .

An application signals that it wants a transaction to be read-only by calling `Connection.setReadOnly(true)`, this replication-aware connection will use one of the slave connections, which are load-balanced per-vm using a round-robin scheme (a given connection is sticky to a slave unless that slave is removed from service). If you have a write transaction, or if you have a read that is time-sensitive (remember, replication in MySQL is asynchronous), set the connection to be not read-only, by calling `Connection.setReadOnly(false)` and the driver will ensure that further calls are sent to the master MySQL server. The driver takes care of propagating the current state of autocommit, isolation level, and catalog between all of the connections that it uses to accomplish this load balancing functionality.

To enable this functionality, use the " `com.mysql.jdbc.ReplicationDriver` " class when configuring your application server's connection pool or when creating an instance of a JDBC driver for your standalone application. Because it accepts the same URL format as the standard MySQL JDBC driver, `ReplicationDriver` does not currently work with `java.sql.DriverManager` -based connection creation unless it is the only MySQL JDBC driver registered with the `DriverManager` .

Here is a short, simple example of how ReplicationDriver might be used in a standalone application.

    import java.sql.Connection;
    import java.sql.ResultSet;
    import java.util.Properties;

    import com.mysql.jdbc.ReplicationDriver;

    public class ReplicationDriverDemo {

      public static void main(String[] args) throws Exception {
        ReplicationDriver driver = new ReplicationDriver();

        Properties props = new Properties();

        // We want this for failover on the slaves
        props.put("autoReconnect", "true");

        // We want to load balance between the slaves
        props.put("roundRobinLoadBalance", "true");

        props.put("user", "foo");
        props.put("password", "bar");

        //
        // Looks like a normal MySQL JDBC url, with a
        // comma-separated list of hosts, the first
        // being the 'master', the rest being any number
        // of slaves that the driver will load balance against
        //

        Connection conn =
            driver.connect("jdbc:mysql://master,slave1,slave2,slave3/test",
                props);

        //
        // Perform read/write work on the master
        // by setting the read-only flag to "false"
        //

        conn.setReadOnly(false);
        conn.setAutoCommit(false);
        conn.createStatement().executeUpdate("UPDATE some_table ....");
        conn.commit();

        //
        // Now, do a query from a slave, the driver automatically picks one
        // from the list
        //

        conn.setReadOnly(true);

        ResultSet rs =
          conn.createStatement().executeQuery("SELECT a,b FROM alt_table");

         .......
      }
    }

#### 1.4.7. Mapping MySQL Error Numbers to SQLStates

The table below provides a mapping of the MySQL Error Numbers to `SQL States`

Table 1. Mapping of MySQL Error Numbers to SQLStates

MySQL Error Number | MySQL Error Name | Legacy (X/Open) SQLState | SQL Standard SQLState
--- | --- | --- | ---
1022 | ER_DUP_KEY | S1000 | 23000
1037 | ER_OUTOFMEMORY | S1001 | HY001
1038 | ER_OUT_OF_SORTMEMORY | S1001 | HY001
1040 | ER_CON_COUNT_ERROR | 08004 | 08004
1042 | ER_BAD_HOST_ERROR | 08004 | 08S01
1043 | ER_HANDSHAKE_ERROR | 08004 | 08S01
1044 | ER_DBACCESS_DENIED_ERROR | S1000 | 42000
1045 | ER_ACCESS_DENIED_ERROR | 28000 | 28000
1047 | ER_UNKNOWN_COM_ERROR | 08S01 | HY000
1050 | ER_TABLE_EXISTS_ERROR | S1000 | 42S01
1051 | ER_BAD_TABLE_ERROR | 42S02 | 42S02
1052 | ER_NON_UNIQ_ERROR | S1000 | 23000
1053 | ER_SERVER_SHUTDOWN | S1000 | 08S01
1054 | ER_BAD_FIELD_ERROR | S0022 | 42S22
1055 | ER_WRONG_FIELD_WITH_GROUP | S1009 | 42000
1056 | ER_WRONG_GROUP_FIELD | S1009 | 42000
1057 | ER_WRONG_SUM_SELECT | S1009 | 42000
1058 | ER_WRONG_VALUE_COUNT | 21S01 | 21S01
1059 | ER_TOO_LONG_IDENT | S1009 | 42000
1060 | ER_DUP_FIELDNAME | S1009 | 42S21
1061 | ER_DUP_KEYNAME | S1009 | 42000
1062 | ER_DUP_ENTRY | S1009 | 23000
1063 | ER_WRONG_FIELD_SPEC | S1009 | 42000
1064 | ER_PARSE_ERROR | 42000 | 42000
1065 | ER_EMPTY_QUERY | 42000 | 42000
1066 | ER_NONUNIQ_TABLE | S1009 | 42000
1067 | ER_INVALID_DEFAULT | S1009 | 42000
1068 | ER_MULTIPLE_PRI_KEY | S1009 | 42000
1069 | ER_TOO_MANY_KEYS | S1009 | 42000
1070 | ER_TOO_MANY_KEY_PARTS | S1009 | 42000
1071 | ER_TOO_LONG_KEY | S1009 | 42000
1072 | ER_KEY_COLUMN_DOES_NOT_EXITS | S1009 | 42000
1073 | ER_BLOB_USED_AS_KEY | S1009 | 42000
1074 | ER_TOO_BIG_FIELDLENGTH | S1009 | 42000
1075 | ER_WRONG_AUTO_KEY | S1009 | 42000
1080 | ER_FORCING_CLOSE | S1000 | 08S01
1081 | ER_IPSOCK_ERROR | 08S01 | 08S01
1082 | ER_NO_SUCH_INDEX | S1009 | 42S12
1083 | ER_WRONG_FIELD_TERMINATORS | S1009 | 42000
1084 | ER_BLOBS_AND_NO_TERMINATED | S1009 | 42000
1090 | ER_CANT_REMOVE_ALL_FIELDS | S1000 | 42000
1091 | ER_CANT_DROP_FIELD_OR_KEY | S1000 | 42000
1101 | ER_BLOB_CANT_HAVE_DEFAULT | S1000 | 42000
1102 | ER_WRONG_DB_NAME | S1000 | 42000
1103 | ER_WRONG_TABLE_NAME | S1000 | 42000
1104 | ER_TOO_BIG_SELECT | S1000 | 42000
1106 | ER_UNKNOWN_PROCEDURE | S1000 | 42000
1107 | ER_WRONG_PARAMCOUNT_TO_PROCEDURE | S1000 | 42000
1109 | ER_UNKNOWN_TABLE | S1000 | 42S02
1110 | ER_FIELD_SPECIFIED_TWICE | S1000 | 42000
1112 | ER_UNSUPPORTED_EXTENSION | S1000 | 42000
1113 | ER_TABLE_MUST_HAVE_COLUMNS | S1000 | 42000
1115 | ER_UNKNOWN_CHARACTER_SET | S1000 | 42000
1118 | ER_TOO_BIG_ROWSIZE | S1000 | 42000
1120 | ER_WRONG_OUTER_JOIN | S1000 | 42000
1121 | ER_NULL_COLUMN_IN_INDEX | S1000 | 42000
1129 | ER_HOST_IS_BLOCKED | 08004 | HY000
1130 | ER_HOST_NOT_PRIVILEGED | 08004 | HY000
1131 | ER_PASSWORD_ANONYMOUS_USER | S1000 | 42000
1132 | ER_PASSWORD_NOT_ALLOWED | S1000 | 42000
1133 | ER_PASSWORD_NO_MATCH | S1000 | 42000
1136 | ER_WRONG_VALUE_COUNT_ON_ROW | S1000 | 21S01
1138 | ER_INVALID_USE_OF_NULL | S1000 | 42000
1139 | ER_REGEXP_ERROR | S1000 | 42000
1140 | ER_MIX_OF_GROUP_FUNC_AND_FIELDS | S1000 | 42000
1141 | ER_NONEXISTING_GRANT | S1000 | 42000
1142 | ER_TABLEACCESS_DENIED_ERROR | S1000 | 42000
1143 | ER_COLUMNACCESS_DENIED_ERROR | S1000 | 42000
1144 | ER_ILLEGAL_GRANT_FOR_TABLE | S1000 | 42000
1145 | ER_GRANT_WRONG_HOST_OR_USER | S1000 | 42000
1146 | ER_NO_SUCH_TABLE | S1000 | 42S02
1147 | ER_NONEXISTING_TABLE_GRANT | S1000 | 42000
1148 | ER_NOT_ALLOWED_COMMAND | S1000 | 42000
1149 | ER_SYNTAX_ERROR | S1000 | 42000
1152 | ER_ABORTING_CONNECTION | S1000 | 08S01
1153 | ER_NET_PACKET_TOO_LARGE | S1000 | 08S01
1154 | ER_NET_READ_ERROR_FROM_PIPE | S1000 | 08S01
1155 | ER_NET_FCNTL_ERROR | S1000 | 08S01
1156 | ER_NET_PACKETS_OUT_OF_ORDER | S1000 | 08S01
1157 | ER_NET_UNCOMPRESS_ERROR | S1000 | 08S01
1158 | ER_NET_READ_ERROR | S1000 | 08S01
1159 | ER_NET_READ_INTERRUPTED | S1000 | 08S01
1160 | ER_NET_ERROR_ON_WRITE | S1000 | 08S01
1161 | ER_NET_WRITE_INTERRUPTED | S1000 | 08S01
1162 | ER_TOO_LONG_STRING | S1000 | 42000
1163 | ER_TABLE_CANT_HANDLE_BLOB | S1000 | 42000
1164 | ER_TABLE_CANT_HANDLE_AUTO_INCREMENT | S1000 | 42000
1166 | ER_WRONG_COLUMN_NAME | S1000 | 42000
1167 | ER_WRONG_KEY_COLUMN | S1000 | 42000
1169 | ER_DUP_UNIQUE | S1000 | 23000
1170 | ER_BLOB_KEY_WITHOUT_LENGTH | S1000 | 42000
1171 | ER_PRIMARY_CANT_HAVE_NULL | S1000 | 42000
1172 | ER_TOO_MANY_ROWS | S1000 | 42000
1173 | ER_REQUIRES_PRIMARY_KEY | S1000 | 42000
1177 | ER_CHECK_NO_SUCH_TABLE | S1000 | 42000
1178 | ER_CHECK_NOT_IMPLEMENTED | S1000 | 42000
1179 | ER_CANT_DO_THIS_DURING_AN_TRANSACTION | S1000 | 25000
1184 | ER_NEW_ABORTING_CONNECTION | S1000 | 08S01
1189 | ER_MASTER_NET_READ | S1000 | 08S01
1190 | ER_MASTER_NET_WRITE | S1000 | 08S01
1203 | ER_TOO_MANY_USER_CONNECTIONS | S1000 | 42000
1205 | ER_LOCK_WAIT_TIMEOUT | 41000 | 41000
1207 | ER_READ_ONLY_TRANSACTION | S1000 | 25000
1211 | ER_NO_PERMISSION_TO_CREATE_USER | S1000 | 42000
1213 | ER_LOCK_DEADLOCK | 41000 | 40001
1216 | ER_NO_REFERENCED_ROW | S1000 | 23000
1217 | ER_ROW_IS_REFERENCED | S1000 | 23000
1218 | ER_CONNECT_TO_MASTER | S1000 | 08S01
1222 | ER_WRONG_NUMBER_OF_COLUMNS_IN_SELECT | S1000 | 21000
1226 | ER_USER_LIMIT_REACHED | S1000 | 42000
1230 | ER_NO_DEFAULT | S1000 | 42000
1231 | ER_WRONG_VALUE_FOR_VAR | S1000 | 42000
1232 | ER_WRONG_TYPE_FOR_VAR | S1000 | 42000
1234 | ER_CANT_USE_OPTION_HERE | S1000 | 42000
1235 | ER_NOT_SUPPORTED_YET | S1000 | 42000
1239 | ER_WRONG_FK_DEF | S1000 | 42000
1241 | ER_OPERAND_COLUMNS | S1000 | 21000
1242 | ER_SUBQUERY_NO_1_ROW | S1000 | 21000
1247 | ER_ILLEGAL_REFERENCE | S1000 | 42S22
1248 | ER_DERIVED_MUST_HAVE_ALIAS | S1000 | 42000
1249 | ER_SELECT_REDUCED | S1000 | 01000
1250 | ER_TABLENAME_NOT_ALLOWED_HERE | S1000 | 42000
1251 | ER_NOT_SUPPORTED_AUTH_MODE | S1000 | 08004
1252 | ER_SPATIAL_CANT_HAVE_NULL | S1000 | 42000
1253 | ER_COLLATION_CHARSET_MISMATCH | S1000 | 42000
1261 | ER_WARN_TOO_FEW_RECORDS | S1000 | 01000
1262 | ER_WARN_TOO_MANY_RECORDS | S1000 | 01000
1263 | ER_WARN_NULL_TO_NOTNULL | S1000 | 01000
1264 | ER_WARN_DATA_OUT_OF_RANGE | S1000 | 01000
1265 | ER_WARN_DATA_TRUNCATED | S1000 | 01000
1280 | ER_WRONG_NAME_FOR_INDEX | S1000 | 42000
1281 | ER_WRONG_NAME_FOR_CATALOG | S1000 | 42000
1286 | ER_UNKNOWN_STORAGE_ENGINE | S1000 | 42000

### 1.5. Connector/J Notes and Tips

#### 1.5.1. Basic JDBC Concepts

This section provides some general JDBC background.

##### 1.5.1.1. Connecting to MySQL Using the `DriverManager` Interface

When you are using JDBC outside of an application server, the `DriverManager` class manages the establishment of Connections.

The `DriverManager` needs to be told which JDBC drivers it should try to make Connections with. The easiest way to do this is to use `Class.forName()` on the class that implements the `java.sql.Driver` interface. With MySQL Connector/J, the name of this class is `com.mysql.jdbc.Driver`. With this method, you could use an external configuration file to supply the driver class name and driver parameters to use when connecting to a database.

The following section of Java code shows how you might register MySQL Connector/J from the `main()` method of your application:

    import java.sql.Connection;
    import java.sql.DriverManager;
    import java.sql.SQLException;

    // Notice, do not import com.mysql.jdbc.*
    // or you will have problems!

    public class LoadDriver {
        public static void main(String[] args) {
            try {
                // The newInstance() call is a work around for some
                // broken Java implementations

                Class.forName("com.mysql.jdbc.Driver").newInstance();
            } catch (Exception ex) {
                // handle the error
            }
    }

After the driver has been registered with the `DriverManager`, you can obtain a `Connection` instance that is connected to a particular database by calling `DriverManager.getConnection()`:

Example 1. Obtaining a connection from the `DriverManager`

This example shows how you can obtain a `Connection` instance from the `DriverManager`. There are a few different signatures for the `getConnection()` method. You should see the API documentation that comes with your JDK for more specific information on how to use them.

    import java.sql.Connection;
    import java.sql.DriverManager;
    import java.sql.SQLException;

    ...
    try {
        Connection conn =
           DriverManager.getConnection("jdbc:mysql://localhost/test?" +
                                       "user=monty&password=greatsqldb");

        // Do something with the Connection

       ...
    } catch (SQLException ex) {
        // handle any errors
        System.out.println("SQLException: " + ex.getMessage());
        System.out.println("SQLState: " + ex.getSQLState());
        System.out.println("VendorError: " + ex.getErrorCode());
    }

Once a `Connection` is established, it can be used to create `Statement` and `PreparedStatement` objects, as well as retrieve metadata about the database. This is explained in the following sections.

##### 1.5.1.2. Using Statements to Execute SQL

`Statement` objects allow you to execute basic SQL queries and retrieve the results through the `ResultSet` class which is described later.

To create a `Statement` instance, you call the `createStatement()` method on the `Connection` object you have retrieved via one of the `DriverManager.getConnection()` or `DataSource.getConnection()` methods described earlier.

Once you have a `Statement` instance, you can execute a `SELECT` query by calling the `executeQuery(String)` method with the SQL you want to use.

To update data in the database, use the `executeUpdate(String SQL)` method. This method returns the number of rows affected by the update statement.

If you don't know ahead of time whether the SQL statement will be a `SELECT` or an `UPDATE`/`INSERT`, then you can use the `execute(String SQL)` method. This method will return true if the SQL query was a `SELECT`, or false if it was an `UPDATE`, `INSERT`, or `DELETE` statement. If the statement was a `SELECT` query, you can retrieve the results by calling the `getResultSet()` method. If the statement was an `UPDATE`, `INSERT`, or `DELETE` statement, you can retrieve the affected rows count by calling `getUpdateCount()` on the `Statement` instance.

Example 2. Using java.sql.Statement to execute a `SELECT` query

    // assume that conn is an already created JDBC connection
    Statement stmt = null;
    ResultSet rs = null;

    try {
        stmt = conn.createStatement();
        rs = stmt.executeQuery("SELECT foo FROM bar");

        // or alternatively, if you don't know ahead of time that
        // the query will be a SELECT...

        if (stmt.execute("SELECT foo FROM bar")) {
            rs = stmt.getResultSet();
        }

        // Now do something with the ResultSet ....
    } finally {
        // it is a good idea to release
        // resources in a finally{} block
        // in reverse-order of their creation
        // if they are no-longer needed

        if (rs != null) {
            try {
                rs.close();
            } catch (SQLException sqlEx) { // ignore }

            rs = null;
        }

        if (stmt != null) {
            try {
                stmt.close();
            } catch (SQLException sqlEx) { // ignore }

            stmt = null;
        }
    }

##### 1.5.1.3. Using `CallableStatements` to Execute Stored Procedures

Starting with MySQL server version 5.0 when used with Connector/J 3.1.1 or newer, the `java.sql.CallableStatement` interface is fully implemented with the exception of the `getParameterMetaData()` method.

For more information on MySQL stored procedures, please refer to http://dev.mysql.com/doc/mysql/en/stored-procedures.html.

Connector/J exposes stored procedure functionality through JDBC's `CallableStatement` interface.

### Note

Current versions of MySQL server do not return enough information for the JDBC driver to provide result set metadata for callable statements. This means that when using `CallableStatement`, `ResultSetMetaData` may return `NULL`.

The following example shows a stored procedure that returns the value of `inOutParam` incremented by 1, and the string passed in via `inputParam` as a `ResultSet`:

Example 3. Stored Procedures

    CREATE PROCEDURE demoSp(IN inputParam VARCHAR(255), \
                                            INOUT inOutParam INT)
    BEGIN
        DECLARE z INT;
        SET z = inOutParam + 1;
        SET inOutParam = z;

        SELECT inputParam;

        SELECT CONCAT('zyxw', inputParam);
    END

To use the `demoSp` procedure with Connector/J, follow these steps:

1. Prepare the callable statement by using `Connection.prepareCall()` .

   Notice that you have to use JDBC escape syntax, and that the parentheses surrounding the parameter placeholders are not optional:

   Example 4. Using `Connection.prepareCall()`

       import java.sql.CallableStatement;

       ...

           //
           // Prepare a call to the stored procedure 'demoSp'
           // with two parameters
           //
           // Notice the use of JDBC-escape syntax ({call ...})
           //

           CallableStatement cStmt = conn.prepareCall("{call demoSp(?, ?)}");

           cStmt.setString(1, "abcdefg");

   ### Note

   `Connection.prepareCall()` is an expensive method, due to the metadata retrieval that the driver performs to support output parameters. For performance reasons, you should try to minimize unnecessary calls to `Connection.prepareCall()` by reusing `CallableStatement` instances in your code.

2. Register the output parameters (if any exist)

   To retrieve the values of output parameters (parameters specified as `OUT` or `INOUT` when you created the stored procedure), JDBC requires that they be specified before statement execution using the various `registerOutputParameter()` methods in the `CallableStatement` interface:

   Example 5. Registering output parameters

       import java.sql.Types;
       ...
       //
       // Connector/J supports both named and indexed
       // output parameters. You can register output
       // parameters using either method, as well
       // as retrieve output parameters using either
       // method, regardless of what method was
       // used to register them.
       //
       // The following examples show how to use
       // the various methods of registering
       // output parameters (you should of course
       // use only one registration per parameter).
       //

       //
       // Registers the second parameter as output, and
       // uses the type 'INTEGER' for values returned from
       // getObject()
       //

       cStmt.registerOutParameter(2, Types.INTEGER);

       //
       // Registers the named parameter 'inOutParam', and
       // uses the type 'INTEGER' for values returned from
       // getObject()
       //

       cStmt.registerOutParameter("inOutParam", Types.INTEGER);
       ...

3. Set the input parameters (if any exist)

   Input and in/out parameters are set as for `PreparedStatement` objects. However, `CallableStatement` also supports setting parameters by name:

   Example 6. Setting `CallableStatement` input parameters

       ...

           //
           // Set a parameter by index
           //

           cStmt.setString(1, "abcdefg");

           //
           // Alternatively, set a parameter using
           // the parameter name
           //

           cStmt.setString("inputParameter", "abcdefg");

           //
           // Set the 'in/out' parameter using an index
           //

           cStmt.setInt(2, 1);

           //
           // Alternatively, set the 'in/out' parameter
           // by name
           //

           cStmt.setInt("inOutParam", 1);

       ...

4. Execute the `CallableStatement`, and retrieve any result sets or output parameters.

   Although `CallableStatement` supports calling any of the `Statement` execute methods (`executeUpdate()`, `executeQuery()` or `execute()`), the most flexible method to call is `execute()`, as you do not need to know ahead of time if the stored procedure returns result sets:

   Example 7. Retrieving results and output parameter values

       ...

           boolean hadResults = cStmt.execute();

           //
           // Process all returned result sets
           //

           while (hadResults) {
               ResultSet rs = cStmt.getResultSet();

               // process result set
               ...

               hadResults = rs.getMoreResults();
           }

           //
           // Retrieve output parameters
           //
           // Connector/J supports both index-based and
           // name-based retrieval
           //

           int outputValue = cStmt.getInt(2); // index-based

           outputValue = cStmt.getInt("inOutParam"); // name-based

       ...

##### 1.5.1.4. Retrieving `AUTO_INCREMENT` Column Values

Before version 3.0 of the JDBC API, there was no standard way of retrieving key values from databases that supported auto increment or identity columns. With older JDBC drivers for MySQL, you could always use a MySQL-specific method on the `Statement` interface, or issue the query `SELECT LAST_INSERT_ID()` after issuing an `INSERT` to a table that had an `AUTO_INCREMENT` key. Using the MySQL-specific method call isn't portable, and issuing a `SELECT` to get the `AUTO_INCREMENT` key's value requires another round-trip to the database, which isn't as efficient as possible. The following code snippets demonstrate the three different ways to retrieve `AUTO_INCREMENT` values. First, we demonstrate the use of the new JDBC-3.0 method `getGeneratedKeys()` which is now the preferred method to use if you need to retrieve `AUTO_INCREMENT` keys and have access to JDBC-3.0. The second example shows how you can retrieve the same value using a standard `SELECT LAST_INSERT_ID()` query. The final example shows how updatable result sets can retrieve the `AUTO_INCREMENT` value when using the `insertRow()` method.

Example 8. Retrieving `AUTO_INCREMENT` column values using `Statement.getGeneratedKeys()`

       Statement stmt = null;
       ResultSet rs = null;

       try {

        //
        // Create a Statement instance that we can use for
        // 'normal' result sets assuming you have a
        // Connection 'conn' to a MySQL database already
        // available

        stmt = conn.createStatement(java.sql.ResultSet.TYPE_FORWARD_ONLY,
                                    java.sql.ResultSet.CONCUR_UPDATABLE);

        //
        // Issue the DDL queries for the table for this example
        //

        stmt.executeUpdate("DROP TABLE IF EXISTS autoIncTutorial");
        stmt.executeUpdate(
                "CREATE TABLE autoIncTutorial ("
                + "priKey INT NOT NULL AUTO_INCREMENT, "
                + "dataField VARCHAR(64), PRIMARY KEY (priKey))");

        //
        // Insert one row that will generate an AUTO INCREMENT
        // key in the 'priKey' field
        //

        stmt.executeUpdate(
                "INSERT INTO autoIncTutorial (dataField) "
                + "values ('Can I Get the Auto Increment Field?')",
                Statement.RETURN_GENERATED_KEYS);

        //
        // Example of using Statement.getGeneratedKeys()
        // to retrieve the value of an auto-increment
        // value
        //

        int autoIncKeyFromApi = -1;

        rs = stmt.getGeneratedKeys();

        if (rs.next()) {
            autoIncKeyFromApi = rs.getInt(1);
        } else {

            // throw an exception from here
        }

        rs.close();

        rs = null;

        System.out.println("Key returned from getGeneratedKeys():"
            + autoIncKeyFromApi);
    } finally {

        if (rs != null) {
            try {
                rs.close();
            } catch (SQLException ex) {
                // ignore
            }
        }

        if (stmt != null) {
            try {
                stmt.close();
            } catch (SQLException ex) {
                // ignore
            }
        }
    }

Example 9. Retrieving `AUTO_INCREMENT` column values using `SELECT LAST_INSERT_ID()`

       Statement stmt = null;
       ResultSet rs = null;

       try {

        //
        // Create a Statement instance that we can use for
        // 'normal' result sets.

        stmt = conn.createStatement();

        //
        // Issue the DDL queries for the table for this example
        //

        stmt.executeUpdate("DROP TABLE IF EXISTS autoIncTutorial");
        stmt.executeUpdate(
                "CREATE TABLE autoIncTutorial ("
                + "priKey INT NOT NULL AUTO_INCREMENT, "
                + "dataField VARCHAR(64), PRIMARY KEY (priKey))");

        //
        // Insert one row that will generate an AUTO INCREMENT
        // key in the 'priKey' field
        //

        stmt.executeUpdate(
                "INSERT INTO autoIncTutorial (dataField) "
                + "values ('Can I Get the Auto Increment Field?')");

        //
        // Use the MySQL LAST_INSERT_ID()
        // function to do the same thing as getGeneratedKeys()
        //

        int autoIncKeyFromFunc = -1;
        rs = stmt.executeQuery("SELECT LAST_INSERT_ID()");

        if (rs.next()) {
            autoIncKeyFromFunc = rs.getInt(1);
        } else {
            // throw an exception from here
        }

        rs.close();

        System.out.println("Key returned from " +
                           "'SELECT LAST_INSERT_ID()': " +
                           autoIncKeyFromFunc);

    } finally {

        if (rs != null) {
            try {
                rs.close();
            } catch (SQLException ex) {
                // ignore
            }
        }

        if (stmt != null) {
            try {
                stmt.close();
            } catch (SQLException ex) {
                // ignore
            }
        }
    }

Example 10. Retrieving `AUTO_INCREMENT` column values in `Updatable ResultSets`

       Statement stmt = null;
       ResultSet rs = null;

       try {

        //
        // Create a Statement instance that we can use for
        // 'normal' result sets as well as an 'updatable'
        // one, assuming you have a Connection 'conn' to
        // a MySQL database already available
        //

        stmt = conn.createStatement(java.sql.ResultSet.TYPE_FORWARD_ONLY,
                                    java.sql.ResultSet.CONCUR_UPDATABLE);

        //
        // Issue the DDL queries for the table for this example
        //

        stmt.executeUpdate("DROP TABLE IF EXISTS autoIncTutorial");
        stmt.executeUpdate(
                "CREATE TABLE autoIncTutorial ("
                + "priKey INT NOT NULL AUTO_INCREMENT, "
                + "dataField VARCHAR(64), PRIMARY KEY (priKey))");

        //
        // Example of retrieving an AUTO INCREMENT key
        // from an updatable result set
        //

        rs = stmt.executeQuery("SELECT priKey, dataField "
           + "FROM autoIncTutorial");

        rs.moveToInsertRow();

        rs.updateString("dataField", "AUTO INCREMENT here?");
        rs.insertRow();

        //
        // the driver adds rows at the end
        //

        rs.last();

        //
        // We should now be on the row we just inserted
        //

        int autoIncKeyFromRS = rs.getInt("priKey");

        rs.close();

        rs = null;

        System.out.println("Key returned for inserted row: "
            + autoIncKeyFromRS);

    } finally {

        if (rs != null) {
            try {
                rs.close();
            } catch (SQLException ex) {
                // ignore
            }
        }

        if (stmt != null) {
            try {
                stmt.close();
            } catch (SQLException ex) {
                // ignore
            }
        }
    }

When you run the preceding example code, you should get the following output: Key returned from `getGeneratedKeys()`: 1 Key returned from `SELECT LAST_INSERT_ID()`: 1 Key returned for inserted row: 2 You should be aware, that at times, it can be tricky to use the `SELECT LAST_INSERT_ID()` query, as that function's value is scoped to a connection. So, if some other query happens on the same connection, the value will be overwritten. On the other hand, the `getGeneratedKeys()` method is scoped by the `Statement` instance, so it can be used even if other queries happen on the same connection, but not on the same `Statement` instance.

#### 1.5.2. Using Connector/J with J2EE and Other Java Frameworks

This section describes how to use Connector/J in several contexts.

##### 1.5.2.1. General J2EE Concepts

This section provides general background on J2EE concepts that pertain to use of Connector/J.

###### 1.5.2.1.1. Understanding Connection Pooling

Connection pooling is a technique of creating and managing a pool of connections that are ready for use by any thread that needs them.

This technique of pooling connections is based on the fact that most applications only need a thread to have access to a JDBC connection when they are actively processing a transaction, which usually take only milliseconds to complete. When not processing a transaction, the connection would otherwise sit idle. Instead, connection pooling allows the idle connection to be used by some other thread to do useful work.

In practice, when a thread needs to do work against a MySQL or other database with JDBC, it requests a connection from the pool. When the thread is finished using the connection, it returns it to the pool, so that it may be used by any other threads that want to use it.

When the connection is loaned out from the pool, it is used exclusively by the thread that requested it. From a programming point of view, it is the same as if your thread called `DriverManager.getConnection()` every time it needed a JDBC connection, however with connection pooling, your thread may end up using either a new, or already-existing connection.

Connection pooling can greatly increase the performance of your Java application, while reducing overall resource usage. The main benefits to connection pooling are:

- Reduced connection creation time

  Although this is not usually an issue with the quick connection setup that MySQL offers compared to other databases, creating new JDBC connections still incurs networking and JDBC driver overhead that will be avoided if connections are recycled.

- Simplified programming model

  When using connection pooling, each individual thread can act as though it has created its own JDBC connection, allowing you to use straight-forward JDBC programming techniques.

- Controlled resource usage

  If you don't use connection pooling, and instead create a new connection every time a thread needs one, your application's resource usage can be quite wasteful and lead to unpredictable behavior under load.

Remember that each connection to MySQL has overhead (memory, CPU, context switches, and so forth) on both the client and server side. Every connection limits how many resources there are available to your application as well as the MySQL server. Many of these resources will be used whether or not the connection is actually doing any useful work!

Connection pools can be tuned to maximize performance, while keeping resource utilization below the point where your application will start to fail rather than just run slower.

Luckily, Sun has standardized the concept of connection pooling in JDBC through the JDBC-2.0 Optional interfaces, and all major application servers have implementations of these APIs that work fine with MySQL Connector/J.

Generally, you configure a connection pool in your application server configuration files, and access it via the Java Naming and Directory Interface (JNDI). The following code shows how you might use a connection pool from an application deployed in a J2EE application server:

Example 11. Using a connection pool with a J2EE application server

    import java.sql.Connection;
    import java.sql.SQLException;
    import java.sql.Statement;

    import javax.naming.InitialContext;
    import javax.sql.DataSource;

    public class MyServletJspOrEjb {

        public void doSomething() throws Exception {
            /*
             * Create a JNDI Initial context to be able to
             *  lookup  the DataSource
             *
             * In production-level code, this should be cached as
             * an instance or static variable, as it can
             * be quite expensive to create a JNDI context.
             *
             * Note: This code only works when you are using servlets
             * or EJBs in a J2EE application server. If you are
             * using connection pooling in standalone Java code, you
             * will have to create/configure datasources using whatever
             * mechanisms your particular connection pooling library
             * provides.
             */

            InitialContext ctx = new InitialContext();

             /*
              * Lookup the DataSource, which will be backed by a pool
              * that the application server provides. DataSource instances
              * are also a good candidate for caching as an instance
              * variable, as JNDI lookups can be expensive as well.
              */

            DataSource ds =
              (DataSource)ctx.lookup("java:comp/env/jdbc/MySQLDB");

            /*
             * The following code is what would actually be in your
             * Servlet, JSP or EJB 'service' method...where you need
             * to work with a JDBC connection.
             */

            Connection conn = null;
            Statement stmt = null;

            try {
                conn = ds.getConnection();

                /*
                 * Now, use normal JDBC programming to work with
                 * MySQL, making sure to close each resource when you're
                 * finished with it, which allows the connection pool
                 * resources to be recovered as quickly as possible
                 */

                stmt = conn.createStatement();
                stmt.execute("SOME SQL QUERY");

                stmt.close();
                stmt = null;

                conn.close();
                conn = null;
            } finally {
                /*
                 * close any jdbc instances here that weren't
                 * explicitly closed during normal code path, so
                 * that we don't 'leak' resources...
                 */

                if (stmt != null) {
                    try {
                        stmt.close();
                    } catch (sqlexception sqlex) {
                        // ignore -- as we can't do anything about it here
                    }

                    stmt = null;
                }

                if (conn != null) {
                    try {
                        conn.close();
                    } catch (sqlexception sqlex) {
                        // ignore -- as we can't do anything about it here
                    }

                    conn = null;
                }
            }
        }
    }

As shown in the example above, after obtaining the JNDI InitialContext, and looking up the DataSource, the rest of the code should look familiar to anyone who has done JDBC programming in the past.

The most important thing to remember when using connection pooling is to make sure that no matter what happens in your code (exceptions, flow-of-control, and so forth), connections, and anything created by them (such as statements or result sets) are closed, so that they may be re-used, otherwise they will be stranded, which in the best case means that the MySQL server resources they represent (such as buffers, locks, or sockets) may be tied up for some time, or worst case, may be tied up forever.

What's the Best Size for my Connection Pool?

As with all other configuration rules-of-thumb, the answer is: it depends. Although the optimal size depends on anticipated load and average database transaction time, the optimum connection pool size is smaller than you might expect. If you take Sun's Java Petstore blueprint application for example, a connection pool of 15-20 connections can serve a relatively moderate load (600 concurrent users) using MySQL and Tomcat with response times that are acceptable.

To correctly size a connection pool for your application, you should create load test scripts with tools such as Apache JMeter or The Grinder, and load test your application.

An easy way to determine a starting point is to configure your connection pool's maximum number of connections to be unbounded, run a load test, and measure the largest amount of concurrently used connections. You can then work backward from there to determine what values of minimum and maximum pooled connections give the best performance for your particular application.

##### 1.5.2.2. Using Connector/J with Tomcat

The following instructions are based on the instructions for Tomcat-5.x, available at http://jakarta.apache.org/tomcat/tomcat-5.0-doc/jndi-datasource-examples-howto.html which is current at the time this document was written.

First, install the .jar file that comes with Connector/J in `$CATALINA_HOME/common/lib` so that it is available to all applications installed in the container.

Next, Configure the JNDI DataSource by adding a declaration resource to `$CATALINA_HOME/conf/server.xml` in the context that defines your web application:

    <Context ....>

      ...

      <Resource name="jdbc/MySQLDB"
                   auth="Container"
                   type="javax.sql.DataSource"/>

      <!-- The name you used above, must match _exactly_ here!

           The connection pool will be bound into JNDI with the name
           "java:/comp/env/jdbc/MySQLDB"
      -->

      <ResourceParams name="jdbc/MySQLDB">
        <parameter>
          <name>factory</name>
          <value>org.apache.commons.dbcp.BasicDataSourceFactory</value>
        </parameter>

        <!-- Don't set this any higher than max_connections on your
             MySQL server, usually this should be a 10 or a few 10's
             of connections, not hundreds or thousands -->

        <parameter>
          <name>maxActive</name>
          <value>10</value>
        </parameter>

        <!-- You don't want to many idle connections hanging around
             if you can avoid it, only enough to soak up a spike in
             the load -->

        <parameter>
          <name>maxIdle</name>
          <value>5</value>
        </parameter>

        <!-- Don't use autoReconnect=true, it's going away eventually
             and it's a crutch for older connection pools that couldn't
             test connections. You need to decide whether your application
             is supposed to deal with SQLExceptions (hint, it should), and
             how much of a performance penalty you're willing to pay
             to ensure 'freshness' of the connection -->

        <parameter>
          <name>validationQuery</name>
          <value>SELECT 1</value>
        </parameter>

       <!-- The most conservative approach is to test connections
            before they're given to your application. For most applications
            this is okay, the query used above is very small and takes
            no real server resources to process, other than the time used
            to traverse the network.

            If you have a high-load application you'll need to rely on
            something else. -->

        <parameter>
          <name>testOnBorrow</name>
          <value>true</value>
        </parameter>

       <!-- Otherwise, or in addition to testOnBorrow, you can test
            while connections are sitting idle -->

        <parameter>
          <name>testWhileIdle</name>
          <value>true</value>
        </parameter>

        <!-- You have to set this value, otherwise even though
             you've asked connections to be tested while idle,
             the idle evicter thread will never run -->

        <parameter>
          <name>timeBetweenEvictionRunsMillis</name>
          <value>10000</value>
        </parameter>

        <!-- Don't allow connections to hang out idle too long,
             never longer than what wait_timeout is set to on the
             server...A few minutes or even fraction of a minute
             is sometimes okay here, it depends on your application
             and how much spikey load it will see -->

        <parameter>
          <name>minEvictableIdleTimeMillis</name>
          <value>60000</value>
        </parameter>

        <!-- Username and password used when connecting to MySQL -->

        <parameter>
         <name>username</name>
         <value>someuser</value>
        </parameter>

        <parameter>
         <name>password</name>
         <value>somepass</value>
        </parameter>

        <!-- Class name for the Connector/J driver -->

        <parameter>
           <name>driverClassName</name>
           <value>com.mysql.jdbc.Driver</value>
        </parameter>

        <!-- The JDBC connection url for connecting to MySQL, notice
             that if you want to pass any other MySQL-specific parameters
             you should pass them here in the URL, setting them using the
             parameter tags above will have no effect, you will also
             need to use &amp; to separate parameter values as the
             ampersand is a reserved character in XML -->

        <parameter>
          <name>url</name>
          <value>jdbc:mysql://localhost:3306/test</value>
        </parameter>

      </ResourceParams>
    </Context>

In general, you should follow the installation instructions that come with your version of Tomcat, as the way you configure datasources in Tomcat changes from time-to-time, and unfortunately if you use the wrong syntax in your XML file, you will most likely end up with an exception similar to the following:

    Error: java.sql.SQLException: Cannot load JDBC driver class 'null ' SQL
    state: null

##### 1.5.2.3. Using Connector/J with JBoss

These instructions cover JBoss-4.x. To make the JDBC driver classes available to the application server, copy the .jar file that comes with Connector/J to the `lib` directory for your server configuration (which is usually called `default`). Then, in the same configuration directory, in the subdirectory named deploy, create a datasource configuration file that ends with "-ds.xml", which tells JBoss to deploy this file as a JDBC Datasource. The file should have the following contents:

    <datasources>
        <local-tx-datasource>
            <!-- This connection pool will be bound into JNDI with the name
                 "java:/MySQLDB" -->

            <jndi-name>MySQLDB</jndi-name>
            <connection-url>jdbc:mysql://localhost:3306/dbname</connection-url>
            <driver-class>com.mysql.jdbc.Driver</driver-class>
            <user-name>user</user-name>
            <password>pass</password>

            <min-pool-size>5</min-pool-size>

            <!-- Don't set this any higher than max_connections on your
             MySQL server, usually this should be a 10 or a few 10's
             of connections, not hundreds or thousands -->

            <max-pool-size>20</max-pool-size>

            <!-- Don't allow connections to hang out idle too long,
             never longer than what wait_timeout is set to on the
             server...A few minutes is usually okay here,
             it depends on your application
             and how much spikey load it will see -->

            <idle-timeout-minutes>5</idle-timeout-minutes>

            <!-- If you're using Connector/J 3.1.8 or newer, you can use
                 our implementation of these to increase the robustness
                 of the connection pool. -->

            <exception-sorter-class-name>
      com.mysql.jdbc.integration.jboss.ExtendedMysqlExceptionSorter
            </exception-sorter-class-name>
            <valid-connection-checker-class-name>
      com.mysql.jdbc.integration.jboss.MysqlValidConnectionChecker
            </valid-connection-checker-class-name>

        </local-tx-datasource>
    </datasources>

##### 1.5.2.4. Using Connector/J with Spring

The Spring Framework is a Java-based application framework designed for assisting in application design by providing a way to configure components. The technique used by Spring is a well known design pattern called Dependency Injection (see Inversion of Control Containers and the Dependency Injection pattern). This article will focus on Java-oriented access to MySQL databases with Spring 2.0. For those wondering, there is a .NET port of Spring appropriately named Spring.NET.

Spring is not only a system for configuring components, but also includes support for aspect oriented programming (AOP). This is one of the main benefits and the foundation for Spring's resource and transaction management. Spring also provides utilities for integrating resource management with JDBC and Hibernate.

For the examples in this section the MySQL world sample database will be used. The first task is to setup a MySQL data source through Spring. Components within Spring use the "bean" terminology. For example, to configure a connection to a MySQL server supporting the world sample database you might use:

    <util:map id="dbProps">
        <entry key="db.driver" value="com.mysql.jdbc.Driver"/>
        <entry key="db.jdbcurl" value="jdbc:mysql://localhost/world"/>
        <entry key="db.username" value="myuser"/>
        <entry key="db.password" value="mypass"/>
    </util:map>

In the above example we are assigning values to properties that will be used in the configuration. For the datasource configuration:

    <bean id="dataSource"
           class="org.springframework.jdbc.datasource.DriverManagerDataSource">
        <property name="driverClassName" value="${db.driver}"/>
        <property name="url" value="${db.jdbcurl}"/>
        <property name="username" value="${db.username}"/>
        <property name="password" value="${db.password}"/>
    </bean>

The placeholders are used to provide values for properties of this bean. This means that you can specify all the properties of the configuration in one place instead of entering the values for each property on each bean. We do, however, need one more bean to pull this all together. The last bean is responsible for actually replacing the placeholders with the property values.

    <bean
     class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
        <property name="properties" ref="dbProps"/>
    </bean>

Now that we have our MySQL data source configured and ready to go, we write some Java code to access it. The example below will retrieve three random cities and their corresponding country using the data source we configured with Spring.

    // Create a new application context. this processes the Spring config
    ApplicationContext ctx =
        new ClassPathXmlApplicationContext("ex1appContext.xml");
    // Retrieve the data source from the application context
        DataSource ds = (DataSource) ctx.getBean("dataSource");
    // Open a database connection using Spring's DataSourceUtils
    Connection c = DataSourceUtils.getConnection(ds);
    try {
        // retrieve a list of three random cities
        PreparedStatement ps = c.prepareStatement(
            "select City.Name as 'City', Country.Name as 'Country' " +
            "from City inner join Country on City.CountryCode = Country.Code " +
            "order by rand() limit 3");
        ResultSet rs = ps.executeQuery();
        while(rs.next()) {
            String city = rs.getString("City");
            String country = rs.getString("Country");
            System.out.printf("The city %s is in %s%n", city, country);
        }
    } catch (SQLException ex) {
        // something has failed and we print a stack trace to analyse the error
        ex.printStackTrace();
        // ignore failure closing connection
        try { c.close(); } catch (SQLException e) { }
    } finally {
        // properly release our connection
        DataSourceUtils.releaseConnection(c, ds);
    }

This is very similar to normal JDBC access to MySQL with the main difference being that we are using DataSourceUtils instead of the DriverManager to create the connection.

While it may seem like a small difference, the implications are somewhat far reaching. Spring manages this resource in a way similar to a container managed data source in a J2EE application server. When a connection is opened, it can be subsequently accessed in other parts of the code if it is synchronized with a transaction. This makes it possible to treat different parts of your application as transactional instead of passing around a database connection.

###### 1.5.2.4.1. Using `JdbcTemplate`

Spring makes extensive use of the Template method design pattern (see Template Method Pattern). Our immediate focus will be on the `JdbcTemplate` and related classes, specifically `NamedParameterJdbcTemplate`. The template classes handle obtaining and releasing a connection for data access when one is needed.

The next example shows how to use `NamedParameterJdbcTemplate` inside of a DAO (Data Access Object) class to retrieve a random city given a country code.

    public class Ex2JdbcDao {
         /**
         * Data source reference which will be provided by Spring.
         */
         private DataSource dataSource;

         /**
         * Our query to find a random city given a country code. Notice
         * the ":country" parameter towards the end. This is called a
         * named parameter.
         */
         private String queryString = "select Name from City " +
            "where CountryCode = :country order by rand() limit 1";

         /**
         * Retrieve a random city using Spring JDBC access classes.
         */
         public String getRandomCityByCountryCode(String cntryCode) {
             // A template that allows using queries with named parameters
             NamedParameterJdbcTemplate template =
             new NamedParameterJdbcTemplate(dataSource);
             // A java.util.Map is used to provide values for the parameters
             Map params = new HashMap();
             params.put("country", cntryCode);
             // We query for an Object and specify what class we are expecting
             return (String)template.queryForObject(queryString, params, String.class);
         }

        /**
        * A JavaBean setter-style method to allow Spring to inject the data source.
        * @param dataSource
        */
        public void setDataSource(DataSource dataSource) {
            this.dataSource = dataSource;
        }
    }

The focus in the above code is on the `getRandomCityByCountryCode()` method. We pass a country code and use the `NamedParameterJdbcTemplate` to query for a city. The country code is placed in a Map with the key "country", which is the parameter is named in the SQL query.

To access this code, you need to configure it with Spring by providing a reference to the data source.

    <bean id="dao" class="code.Ex2JdbcDao">
        <property name="dataSource" ref="dataSource"/>
    </bean>

At this point, we can just grab a reference to the DAO from Spring and call `getRandomCityByCountryCode()`.

    // Create the application context
        ApplicationContext ctx =
        new ClassPathXmlApplicationContext("ex2appContext.xml");
        // Obtain a reference to our DAO
        Ex2JdbcDao dao = (Ex2JdbcDao) ctx.getBean("dao");

        String countryCode = "USA";

        // Find a few random cities in the US
        for(int i = 0; i < 4; ++i)
            System.out.printf("A random city in %s is %s%n", countryCode,
                dao.getRandomCityByCountryCode(countryCode));

This example shows how to use Spring's JDBC classes to completely abstract away the use of traditional JDBC classes including `Connection` and `PreparedStatement`.

###### 1.5.2.4.2. Transactional JDBC Access

You might be wondering how we can add transactions into our code if we don't deal directly with the JDBC classes. Spring provides a transaction management package that not only replaces JDBC transaction management, but also allows declarative transaction management (configuration instead of code).

In order to use transactional database access, we will need to change the storage engine of the tables in the world database. The downloaded script explicitly creates MyISAM tables which do not support transactional semantics. The InnoDB storage engine does support transactions and this is what we will be using. We can change the storage engine with the following statements.

    ALTER TABLE City ENGINE=InnoDB;
    ALTER TABLE Country ENGINE=InnoDB;
    ALTER TABLE CountryLanguage ENGINE=InnoDB;

A good programming practice emphasized by Spring is separating interfaces and implementations. What this means is that we can create a Java interface and only use the operations on this interface without any internal knowledge of what the actual implementation is. We will let Spring manage the implementation and with this it will manage the transactions for our implementation.

First you create a simple interface:

    public interface Ex3Dao {
        Integer createCity(String name, String countryCode,
        String district, Integer population);
    }

This interface contains one method that will create a new city record in the database and return the id of the new record. Next you need to create an implementation of this interface.

    public class Ex3DaoImpl implements Ex3Dao {
        protected DataSource dataSource;
        protected SqlUpdate updateQuery;
        protected SqlFunction idQuery;

        public Integer createCity(String name, String countryCode,
            String district, Integer population) {
                updateQuery.update(new Object[] { name, countryCode,
                       district, population });
                return getLastId();
            }

        protected Integer getLastId() {
            return idQuery.run();
        }
    }

You can see that we only operate on abstract query objects here and don't deal directly with the JDBC API. Also, this is the complete implementation. All of our transaction management will be dealt with in the configuration. To get the configuration started, we need to create the DAO.

    <bean id="dao" class="code.Ex3DaoImpl">
        <property name="dataSource" ref="dataSource"/>
        <property name="updateQuery">...</property>
        <property name="idQuery">...</property>
    </bean>

Now you need to setup the transaction configuration. The first thing you must do is create transaction manager to manage the data source and a specification of what transaction properties are required for for the `dao` methods.

    <bean id="transactionManager"
      class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
        <property name="dataSource" ref="dataSource"/>
    </bean>

    <tx:advice id="txAdvice" transaction-manager="transactionManager">
        <tx:attributes>
            <tx:method name="*"/>
        </tx:attributes>
    </tx:advice>

The preceding code creates a transaction manager that handles transactions for the data source provided to it. The `txAdvice` uses this transaction manager and the attributes specify to create a transaction for all methods. Finally you need to apply this advice with an AOP pointcut.

    <aop:config>
        <aop:pointcut id="daoMethods"
            expression="execution(* code.Ex3Dao.*(..))"/>
         <aop:advisor advice-ref="txAdvice" pointcut-ref="daoMethods"/>
    </aop:config>

This basically says that all methods called on the `Ex3Dao` interface will be wrapped in a transaction. To make use of this, you only have to retrieve the `dao` from the application context and call a method on the `dao` instance.

    Ex3Dao dao = (Ex3Dao) ctx.getBean("dao");
    Integer id = dao.createCity(name,  countryCode, district, pop);

We can verify from this that there is no transaction management happening in our Java code and it's all configured with Spring. This is a very powerful notion and regarded as one of the most beneficial features of Spring.

###### 1.5.2.4.3. Connection Pooling

In many sitations, such as web applications, there will be a large number of small database transactions. When this is the case, it usually makes sense to create a pool of database connections available for web requests as needed. Although MySQL does not spawn an extra process when a connection is made, there is still a small amount of overhead to create and setup the connection. Pooling of connections also alleviates problems such as collecting large amounts of sockets in the `TIME_WAIT` state.

Setting up pooling of MySQL connections with Spring is as simple as changing the data source configuration in the application context. There are a number of configurations that we can use. The first example is based on the Jakarta Commons DBCP library. The example below replaces the source configuration that was based on `DriverManagerDataSource` with DBCP's BasicDataSource.

    <bean id="dataSource" destroy-method="close"
      class="org.apache.commons.dbcp.BasicDataSource">
        <property name="driverClassName" value="${db.driver}"/>
        <property name="url" value="${db.jdbcurl}"/>
        <property name="username" value="${db.username}"/>
        <property name="password" value="${db.password}"/>
        <property name="initialSize" value="3"/>
    </bean>

The configuration of the two solutions is very similar. The difference is that DBCP will pool connections to the database instead of creating a new connection every time one is requested. We have also set a parameter here called `initialSize`. This tells DBCP that we want three connections in the pool when it is created.

Another way to configure connection pooling is to configure a data source in our J2EE application server. Using JBoss as an example, you can set up the MySQL connection pool by creating a file called `mysql-local-ds.xml` and placing it in the server/default/deploy directory in JBoss. Once we have this setup, we can use JNDI to look it up. With Spring, this lookup is very simple. The data source configuration looks like this.

    <jee:jndi-lookup id="dataSource" jndi-name="java:MySQL_DS"/>

#### 1.5.3. Common Problems and Solutions

There are a few issues that seem to be commonly encountered often by users of MySQL Connector/J. This section deals with their symptoms, and their resolutions.

Questions

- 1.5.3.1: When I try to connect to the database with MySQL Connector/J, I get the following exception:

      SQLException: Server configuration denies access to data source
      SQLState: 08001
      VendorError: 0

  What's going on? I can connect just fine with the MySQL command-line client.

- 1.5.3.2: My application throws an SQLException 'No Suitable Driver'. Why is this happening?

- 1.5.3.3: I'm trying to use MySQL Connector/J in an applet or application and I get an exception similar to:

      SQLException: Cannot connect to MySQL server on host:3306.
      Is there a MySQL server running on the machine/port you
      are trying to connect to?

      (java.security.AccessControlException)
      SQLState: 08S01
      VendorError: 0

- 1.5.3.4: I have a servlet/application that works fine for a day, and then stops working overnight

- 1.5.3.5: I'm trying to use JDBC-2.0 updatable result sets, and I get an exception saying my result set is not updatable.

- 1.5.3.6: I cannot connect to the MySQL server using Connector/J, and I'm sure the connection paramters are correct.

- 1.5.3.7: I am trying to connect to my MySQL server within my application, but I get the following error and stack trace:

      java.net.SocketException
      MESSAGE: Software caused connection abort: recv failed

      STACKTRACE:

      java.net.SocketException: Software caused connection abort: recv failed
      at java.net.SocketInputStream.socketRead0(Native Method)
      at java.net.SocketInputStream.read(Unknown Source)
      at com.mysql.jdbc.MysqlIO.readFully(MysqlIO.java:1392)
      at com.mysql.jdbc.MysqlIO.readPacket(MysqlIO.java:1414)
      at com.mysql.jdbc.MysqlIO.doHandshake(MysqlIO.java:625)
      at com.mysql.jdbc.Connection.createNewIO(Connection.java:1926)
      at com.mysql.jdbc.Connection.<init>(Connection.java:452)
      at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:411)

- 1.5.3.8: My application is deployed through JBoss and I am using transactions to handle the statements on the MySQL database. Under heavy loads I am getting a error and stack trace, but these only occur after a fixed period of heavy activity.

- 1.5.3.9: When using gcj an `java.io.CharConversionException` is raised when working with certain character sequences.

- 1.5.3.10: Updating a table that contains a primary key that is either `FLOAT` or compound primary key that uses `FLOAT` fails to update the table and raises an exception.

Questions and Answers

1.5.3.1: When I try to connect to the database with MySQL Connector/J, I get the following exception:

    SQLException: Server configuration denies access to data source
    SQLState: 08001
    VendorError: 0

What's going on? I can connect just fine with the MySQL command-line client.

MySQL Connector/J must use TCP/IP sockets to connect to MySQL, as Java does not support Unix Domain Sockets. Therefore, when MySQL Connector/J connects to MySQL, the security manager in MySQL server will use its grant tables to determine whether the connection should be allowed.

You must add the necessary security credentials to the MySQL server for this to happen, using the `GRANT` statement to your MySQL Server. See `GRANT` Syntax, for more information.

### Note

Testing your connectivity with the mysql command-line client will not work unless you add the `--host` flag, and use something other than `localhost` for the host. The mysql command-line client will use Unix domain sockets if you use the special hostname `localhost`. If you are testing connectivity to `localhost`, use `127.0.0.1` as the hostname instead.

### Warning

Changing privileges and permissions improperly in MySQL can potentially cause your server installation to not have optimal security properties.

1.5.3.2: My application throws an SQLException 'No Suitable Driver'. Why is this happening?

There are three possible causes for this error:

- The Connector/J driver is not in your `CLASSPATH`, see Section 1.2, “Connector/J Installation”.

- The format of your connection URL is incorrect, or you are referencing the wrong JDBC driver.

- When using DriverManager, the `jdbc.drivers` system property has not been populated with the location of the Connector/J driver.

1.5.3.3: I'm trying to use MySQL Connector/J in an applet or application and I get an exception similar to:

    SQLException: Cannot connect to MySQL server on host:3306.
    Is there a MySQL server running on the machine/port you
    are trying to connect to?

    (java.security.AccessControlException)
    SQLState: 08S01
    VendorError: 0

Either you're running an Applet, your MySQL server has been installed with the "--skip-networking" option set, or your MySQL server has a firewall sitting in front of it.

Applets can only make network connections back to the machine that runs the web server that served the .class files for the applet. This means that MySQL must run on the same machine (or you must have some sort of port re-direction) for this to work. This also means that you will not be able to test applets from your local file system, you must always deploy them to a web server.

MySQL Connector/J can only communicate with MySQL using TCP/IP, as Java does not support Unix domain sockets. TCP/IP communication with MySQL might be affected if MySQL was started with the "--skip-networking" flag, or if it is firewalled.

If MySQL has been started with the "--skip-networking" option set (the Debian Linux package of MySQL server does this for example), you need to comment it out in the file /etc/mysql/my.cnf or /etc/my.cnf. Of course your my.cnf file might also exist in the `data` directory of your MySQL server, or anywhere else (depending on how MySQL was compiled for your system). Binaries created by MySQL AB always look in /etc/my.cnf and [datadir]/my.cnf. If your MySQL server has been firewalled, you will need to have the firewall configured to allow TCP/IP connections from the host where your Java code is running to the MySQL server on the port that MySQL is listening to (by default, 3306).

1.5.3.4: I have a servlet/application that works fine for a day, and then stops working overnight

MySQL closes connections after 8 hours of inactivity. You either need to use a connection pool that handles stale connections or use the "autoReconnect" parameter (see Section 1.4.1, “Driver/Datasource Class Names, URL Syntax and Configuration Properties for Connector/J”).

Also, you should be catching SQLExceptions in your application and dealing with them, rather than propagating them all the way until your application exits, this is just good programming practice. MySQL Connector/J will set the SQLState (see `java.sql.SQLException.getSQLState()` in your APIDOCS) to "08S01" when it encounters network-connectivity issues during the processing of a query. Your application code should then attempt to re-connect to MySQL at this point.

The following (simplistic) example shows what code that can handle these exceptions might look like:

Example 12. Example of transaction with retry logic

    public void doBusinessOp() throws SQLException {
        Connection conn = null;
        Statement stmt = null;
        ResultSet rs = null;

        //
        // How many times do you want to retry the transaction
        // (or at least _getting_ a connection)?
        //
        int retryCount = 5;

        boolean transactionCompleted = false;

        do {
            try {
                conn = getConnection(); // assume getting this from a
                                        // javax.sql.DataSource, or the
                                        // java.sql.DriverManager

                conn.setAutoCommit(false);

                //
                // Okay, at this point, the 'retry-ability' of the
                // transaction really depends on your application logic,
                // whether or not you're using autocommit (in this case
                // not), and whether you're using transacational storage
                // engines
                //
                // For this example, we'll assume that it's _not_ safe
                // to retry the entire transaction, so we set retry
                // count to 0 at this point
                //
                // If you were using exclusively transaction-safe tables,
                // or your application could recover from a connection going
                // bad in the middle of an operation, then you would not
                // touch 'retryCount' here, and just let the loop repeat
                // until retryCount == 0.
                //
                retryCount = 0;

                stmt = conn.createStatement();

                String query = "SELECT foo FROM bar ORDER BY baz";

                rs = stmt.executeQuery(query);

                while (rs.next()) {
                }

                rs.close();
                rs = null;

                stmt.close();
                stmt = null;

                conn.commit();
                conn.close();
                conn = null;

                transactionCompleted = true;
            } catch (SQLException sqlEx) {

                //
                // The two SQL states that are 'retry-able' are 08S01
                // for a communications error, and 40001 for deadlock.
                //
                // Only retry if the error was due to a stale connection,
                // communications problem or deadlock
                //

                String sqlState = sqlEx.getSQLState();

                if ("08S01".equals(sqlState) || "40001".equals(sqlState)) {
                    retryCount--;
                } else {
                    retryCount = 0;
                }
            } finally {
                if (rs != null) {
                    try {
                        rs.close();
                    } catch (SQLException sqlEx) {
                        // You'd probably want to log this . . .
                    }
                }

                if (stmt != null) {
                    try {
                        stmt.close();
                    } catch (SQLException sqlEx) {
                        // You'd probably want to log this as well . . .
                    }
                }

                if (conn != null) {
                    try {
                        //
                        // If we got here, and conn is not null, the
                        // transaction should be rolled back, as not
                        // all work has been done

                        try {
                            conn.rollback();
                        } finally {
                            conn.close();
                        }
                    } catch (SQLException sqlEx) {
                        //
                        // If we got an exception here, something
                        // pretty serious is going on, so we better
                        // pass it up the stack, rather than just
                        // logging it. . .

                        throw sqlEx;
                    }
                }
            }
        } while (!transactionCompleted && (retryCount > 0));
    }

### Note

Use of the `autoReconnect` option is not recommended because there is no safe method of reconnecting to the MySQL server without risking some corruption of the connection state or database state information. Instead, you should use a connection pool which will enable your application to connect to the MySQL server using an available connection from the pool. The `autoReconnect` facility is deprecated, and may be removed in a future release.

1.5.3.5: I'm trying to use JDBC-2.0 updatable result sets, and I get an exception saying my result set is not updatable.

Because MySQL does not have row identifiers, MySQL Connector/J can only update result sets that have come from queries on tables that have at least one primary key, the query must select every primary key and the query can only span one table (that is, no joins). This is outlined in the JDBC specification.

Note that this issue only occurs when using updatable result sets, and is caused because Connector/J is unable to guarantee that it can identify the correct rows within the result set to be updated without having a unique reference to each row. There is no requirement to have a unique field on a table if you are using `UPDATE` or `DELETE` statements on a table where you can individually specify the criteria to be matched using a `WHERE` clause.

1.5.3.6: I cannot connect to the MySQL server using Connector/J, and I'm sure the connection paramters are correct.

Make sure that the `skip-networking` option has not been enabled on your server. Connector/J must be able to communicate with your server over TCP/IP, named sockets are not supported. Also ensure that you are not filtering connections through a Firewall or other network security system. For more informaiton, see `Can't connect to [local] MySQL server`.

1.5.3.7: I am trying to connect to my MySQL server within my application, but I get the following error and stack trace:

    java.net.SocketException
    MESSAGE: Software caused connection abort: recv failed

    STACKTRACE:

    java.net.SocketException: Software caused connection abort: recv failed
    at java.net.SocketInputStream.socketRead0(Native Method)
    at java.net.SocketInputStream.read(Unknown Source)
    at com.mysql.jdbc.MysqlIO.readFully(MysqlIO.java:1392)
    at com.mysql.jdbc.MysqlIO.readPacket(MysqlIO.java:1414)
    at com.mysql.jdbc.MysqlIO.doHandshake(MysqlIO.java:625)
    at com.mysql.jdbc.Connection.createNewIO(Connection.java:1926)
    at com.mysql.jdbc.Connection.<init>(Connection.java:452)
    at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:411)

The error probably indicates that you are using a older version of the Connector/J JDBC driver (2.0.14 or 3.0.x) and you are trying to connect to a MySQL server with version 4.1x or newer. The older drivers are not compatible with 4.1 or newer of MySQL as they do not support the newer authentication mechanisms.

It is likely that the older version of the Connector/J driver exists within your application directory or your `CLASSPATH` includes the older Connector/J package.

1.5.3.8: My application is deployed through JBoss and I am using transactions to handle the statements on the MySQL database. Under heavy loads I am getting a error and stack trace, but these only occur after a fixed period of heavy activity.

This is a JBoss, not Connector/J, issue and is connected to the use of transactions. Under heavy loads the time taken for transactions to complete can increase, and the error is caused because you have exceeded the predefined timeout.

You can increase the timeout value by setting the `TransactionTimeout` attribute to the `TransactionManagerService` within the `/conf/jboss-service.xml` file (pre-4.0.3) or `/deploy/jta-service.xml` for JBoss 4.0.3 or later. See TransactionTimeoute within the JBoss wiki for more information.

1.5.3.9: When using gcj an `java.io.CharConversionException` is raised when working with certain character sequences.

This is a known issue with gcj which raises an exception when it reaches an unknown character or one it cannot convert. You should add `useJvmCharsetConverters=true` to your connection string to force character conversion outside of the gcj libraries, or try a different JDK.

1.5.3.10: Updating a table that contains a primary key that is either `FLOAT` or compound primary key that uses `FLOAT` fails to update the table and raises an exception.

Connector/J adds conditions to the `WHERE` clause during an `UPDATE` to check the old values of the primary key. If there is no match then Connector/J considers this a failure condition and raises an exception.

The problem is that rounding differences between supplied values and the values stored in the database may mean that the values never match, and hence the update fails. The issue will affect all queries, not just those from Connector/J.

To prevent this issue, use a primary key that does not use `FLOAT`. If you have to use a floating point column in your primary key use `DOUBLE` or `DECIMAL` types in place of `FLOAT`.

### 1.6. Connector/J Support

#### 1.6.1. Connector/J Community Support

MySQL AB provides assistance to the user community by means of its mailing lists. For Connector/J related issues, you can get help from experienced users by using the MySQL and Java mailing list. Archives and subscription information is available online at http://lists.mysql.com/java.

For information about subscribing to MySQL mailing lists or to browse list archives, visit http://lists.mysql.com/. See MySQL Mailing Lists.

Community support from experienced users is also available through the JDBC Forum. You may also find help from other users in the other MySQL Forums, located at http://forums.mysql.com. See MySQL Community Support at the MySQL Forums.

#### 1.6.2. How to Report Connector/J Bugs or Problems

The normal place to report bugs is http://bugs.mysql.com/, which is the address for our bugs database. This database is public, and can be browsed and searched by anyone. If you log in to the system, you will also be able to enter new reports.

If you have found a sensitive security bug in MySQL, you can send email to security_at_mysql.com.

Writing a good bug report takes patience, but doing it right the first time saves time both for us and for yourself. A good bug report, containing a full test case for the bug, makes it very likely that we will fix the bug in the next release.

This section will help you write your report correctly so that you don't waste your time doing things that may not help us much or at all.

If you have a repeatable bug report, please report it to the bugs database at http://bugs.mysql.com/. Any bug that we are able to repeat has a high chance of being fixed in the next MySQL release.

To report other problems, you can use one of the MySQL mailing lists.

Remember that it is possible for us to respond to a message containing too much information, but not to one containing too little. People often omit facts because they think they know the cause of a problem and assume that some details don't matter.

A good principle is this: If you are in doubt about stating something, state it. It is faster and less troublesome to write a couple more lines in your report than to wait longer for the answer if we must ask you to provide information that was missing from the initial report.

The most common errors made in bug reports are (a) not including the version number of Connector/J or MySQL used, and (b) not fully describing the platform on which Connector/J is installed (including the JVM version, and the platform type and version number that MySQL itself is installed on).

This is highly relevant information, and in 99 cases out of 100, the bug report is useless without it. Very often we get questions like, “Why doesn't this work for me?” Then we find that the feature requested wasn't implemented in that MySQL version, or that a bug described in a report has already been fixed in newer MySQL versions.

Sometimes the error is platform-dependent; in such cases, it is next to impossible for us to fix anything without knowing the operating system and the version number of the platform.

If at all possible, you should create a repeatable, stanalone testcase that doesn't involve any third-party classes.

To streamline this process, we ship a base class for testcases with Connector/J, named '`com.mysql.jdbc.util.BaseBugReport`'. To create a testcase for Connector/J using this class, create your own class that inherits from `com.mysql.jdbc.util.BaseBugReport` and override the methods `setUp()`, `tearDown()` and `runTest()`.

In the `setUp()` method, create code that creates your tables, and populates them with any data needed to demonstrate the bug.

In the `runTest()` method, create code that demonstrates the bug using the tables and data you created in the `setUp` method.

In the `tearDown()` method, drop any tables you created in the `setUp()` method.

In any of the above three methods, you should use one of the variants of the `getConnection()` method to create a JDBC connection to MySQL:

- `getConnection()` - Provides a connection to the JDBC URL specified in `getUrl()`. If a connection already exists, that connection is returned, otherwise a new connection is created.

- `getNewConnection()` - Use this if you need to get a new connection for your bug report (i.e. there's more than one connection involved).

- `getConnection(String url)` - Returns a connection using the given URL.

- `getConnection(String url, Properties props)` - Returns a connection using the given URL and properties.

If you need to use a JDBC URL that is different from 'jdbc:mysql:///test', override the method `getUrl()` as well.

Use the `assertTrue(boolean expression)` and `assertTrue(String failureMessage, boolean expression)` methods to create conditions that must be met in your testcase demonstrating the behavior you are expecting (vs. the behavior you are observing, which is why you are most likely filing a bug report).

Finally, create a `main()` method that creates a new instance of your testcase, and calls the `run` method:

    public static void main(String[] args) throws Exception {
          new MyBugReport().run();
     }

Once you have finished your testcase, and have verified that it demonstrates the bug you are reporting, upload it with your bug report to http://bugs.mysql.com/.

#### 1.6.3. Connector/J Change History

The Connector/J Change History (Changelog) is located with the main Changelog for MySQL. See MySQL Connector/J Change History.