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# 8 - Mapping SQL and Java Types

This overview is excerpted from JDBCTM Database Access from JavaTM: A Tutorial and Annotated Reference, currently in progress at JavaSoft. This book, both a tutorial and the definitive reference manual for JDBC, will be published in the spring of 1997 by Addison-Wesley Publishing Company as part of the Java series.

## 8.1 Overview

Since SQL data types and Java data types are not identical, there needs to be some mechanism for reading and writing data between an application using Java types and a database using SQL types.

To accomplish this, JDBC provides sets of `getXXX` and `setXXX` methods, the method `registerOutParameter`, and the class `Types`.

This section brings together information about data types affecting various classes and interfaces and puts all the tables showing the mappings between SQL types and Java types in one place for easy reference.

## 8.2 Mapping SQL Data Types into Java

Unfortunately there are significant variations between the SQL types supported by different database products. Even when different databases support SQL types with the same semantics, they may give those types different names. For example, most of the major databases support an SQL data type for large binary values, but Oracle calls this type `LONG RAW`, Sybase calls it `IMAGE`, Informix calls it `BYTE`, and DB2 calls it `LONG VARCHAR FOR BIT DATA`.

Fortunately, JDBC programmers will normally not need to concern themselves with the actual SQL type names used by a target database. Most of the time JDBC programmers will be programming against existing database tables, and they need not concern themselves with the exact SQL type names that were used to create these tables.

JDBC defines a set of generic SQL type identifiers in the class `java.sql.Types`. These types have been designed to represent the most commonly used SQL types. In programming with the JDBC API, programmers will normally be able to use these JDBC types to reference generic SQL types, without having to be concerned about the exact SQL type name used by the target database. These JDBC types are fully described in the next section.

The one major place where programmers may need to use SQL type names is in the SQL `CREATE TABLE` statement when they are creating a new database table. In this case programmers must take care to use SQL type names that are supported by their target database. We recommend that you consult your database documentation if you need exact definitions of the behavior of the various SQL types on a particular database.

If you want to be able to write portable JDBC programs that can create tables on a variety of different databases, you have two main choices. First, you can restrict yourself to using only very widely accepted SQL type names such as `INTEGER`, `NUMERIC`, or `VARCHAR`, which are likely to work for all databases. Or second, you can use the `java.sql.DatabaseMetaData.getTypeInfo` method to discover which SQL types are actually supported by a given database and select a database-specific SQL type name that matches a given JDBC type.

JDBC defines a standard mapping from the JDBC database types to Java types. For example, a JDBC `INTEGER` is normally mapped to a Java `int`. This supports a simple interface for reading and writing JDBC values as simple Java types.

The Java types do not need to be exactly isomorphic to the JDBC types; they just need to be able to represent them with enough type information to correctly store and retrieve parameters and recover results from SQL statements. For example, a Java `String` object does not precisely match any of the JDBC `CHAR` types, but it gives enough type information to represent `CHAR`, `VARCHAR`, or `LONGVARCHAR` successfully.

## 8.3 JDBC Types

This section describes the different JDBC data types and how they are related to standard SQL types and to Java types.

### 8.3.1 CHAR, VARCHAR, and LONGVARCHAR

The JDBC types `CHAR`, `VARCHAR`, and `LONGVARCHAR` are closely related. `CHAR` represents a small, fixed-length character string, `VARCHAR` represents a small, variable- length character string, and `LONGVARCHAR` represents a large, variable-length character string.

The SQL `CHAR` type corresponding to JDBC `CHAR` is defined in SQL-92 and is supported by all the major databases. It takes a parameter that specifies the string length. Thus `CHAR(12)` defines a 12-character string. All the major databases support `CHAR` lengths up to at least 254 characters.

The SQL `VARCHAR` type corresponding to JDBC `VARCHAR` is defined in SQL-92 and is supported by all the major databases. It takes a parameter that specifies the maximum length of the string. Thus `VARCHAR(12)` defines a string whose length may be up to 12 characters. All the major databases support `VARCHAR` lengths up to 254 characters. When a string value is assigned to a `VARCHAR` variable, the database remembers the length of the assigned string and on a `SELECT, it` will return the exact original string.

Unfortunately there is no consistent SQL mapping for the JDBC `LONGVARCHAR` type. All the major databases support some kind of very large variable-ength string supporting up to at least a gigabyte of data, but the SQL type names vary.

Java programmers do not need to distinguish among the three types of JDBC strings, `CHAR`, `VARCHAR`, and `LONGVARCHAR`. Each can be expressed as a Java `String`, and it is possible to read and write an SQL statement correctly without knowing the exact data type that was expected.

`CHAR`, `VARCHAR`, and `LONGVARCHAR` could have been mapped to either `String` or `char[]`, but `String` is more appropriate for normal use. Also, the `String` class makes conversions between `String` and `char[]` easy: There is a method for converting a `String` object to a `char[]` and also a constructor for turning a `char[]` into a `String` object.

One issue that had to be addressed is how to handle fixed-length SQL strings of type `CHAR(n)`. The answer is that JDBC drivers (or the DBMS) perform appropriate padding with spaces. Thus, when a `CHAR(n)` field is retrieved from the database, the driver will convert it to a Java `String` object of length `n`, which may include some padding spaces at the end. Conversely, when a `String` object is sent to a `CHAR(n)` field, the driver and/or the database will add any necessary padding spaces to the end of the string to bring it up to length `n`.

The method `ResultSet.getString`, which allocates and returns a new `String` object, is recommended for retrieving data from `CHAR`, `VARCHAR`, and `LONGVARCHAR` fields. This is suitable for retrieving normal data, but can be unwieldy if the JDBC type `LONGVARCHAR` is being used to store multi-megabyte strings. To handle this case, two methods in the `ResultSet` interface allow programmers to retrieve a `LONGVARCHAR` value as a Java input stream from which they can subsequently read data in whatever size chunks they prefer. These methods are `getAsciiStream` and `getUnicodeStream`, which deliver the data stored in a `LONGVARCHAR` column as a stream of Ascii or Unicode characters.

### 8.3.2 BINARY, VARBINARY, and LONGVARBINARY

The JDBC types `BINARY`, `VARBINARY`, and `LONGVARBINARY` are closely related. `BINARY` represents a small, fixed-length binary value, `VARBINARY` represents a small, variable-length binary value, and `LONGVARBINARY` represents a large, variable-length binary value.

Unfortunately, the use of these various `BINARY` types has not been standardized and support varies considerably among the major databases.

The SQL `BINARY` type corresponding to JDBC `BINARY` is a non-standard SQL extension and is only implemented on some databases. It takes a parameter that specifies the number of binary bytes. Thus `BINARY(12)` defines a 12-byte binary type. Typically, `BINARY` values are limited to 254 bytes.

The SQL `VARBINARY` type corresponding to JDBC `VARBINARY` is a non-standard SQL extension and is only implemented on some databases. It takes a parameter that specifies the maximum number of binary bytes. Thus `VARBINARY(12)` defines a binary type whose length may be up to 12 bytes. Typically, `VARBINARY` values are limited to 254 bytes. When a binary value is assigned to a `VARBINARY` variable, the database remembers the length of the assigned value and on a `SELECT`, `it` will return the exact original value.

Regrettably, there is no consistent SQL type name corresponding to the JDBC `LONGVARBINARY` type. All the major databases support some kind of very large variable length binary type supporting up to at least a gigabyte of data, but the SQL type names vary.

`BINARY`, `VARBINARY`, and `LONGVARBINARY` can all be expressed identically as `byte` arrays in Java. Since it is possible to read and write SQL statements correctly without knowing the exact `BINARY` data type that was expected, there is no need for Java programmers to distinguish among them.

The method recommended for retrieving `BINARY` and `VARBINARY` values is `ResultSet.getBytes`. If a column of type JDBC `LONGVARBINARY` stores a byte array that is many megabytes long, however, the method `getBinaryStream` is recommended. Similar to the situation with `LONGVARCHAR`, this method allows a Java programmer to retrieve a `LONGVARBINARY` value as a Java input stream that can be read later in smaller chunks.

### 8.3.3 BIT

The JDBC type `BIT` represents a single bit value that can be zero or one.

SQL-92 defines an SQL `BIT` type. However, unlike the JDBC `BIT` type this SQL-92 BIT type can be used as a parameterized type to define a fixed-length binary string. Fortunately, SQL-92 also permits the use of the simple non-parameterized `BIT` type to represent a single binary digit, and this usage corresponds to the JDBC `BIT` type. Unfortunately, the SQL-92 `BIT` type is only required in "full" SQL-92 and is currently supported by only a subset of the major databases. Portable code may therefore prefer to use the JDBC `SMALLINT` type, which is widely supported.

The recommended Java mapping for the JDBC `BIT` type is as a Java boolean.

### 8.3.4 TINYINT

The JDBC type `TINYINT` represents an 8-bit unsigned integer value between 0 and 255.

The corresponding SQL type, `TINYINT,` is currently supported by only a subset of the major databases. Portable code may therefore prefer to use the JDBC `SMALLINT` type, which is widely supported.

The recommended Java mapping for the JDBC `TINYINT` type is as either a Java `byte` or a Java `short`. The 8-bit Java `byte` type represents a signed value from -128 to 127, so it may not always be appropriate for larger `TINYINT` values, whereas the 16-bit Java `short` will always be able to hold all `TINYINT` values.

### 8.3.5 SMALLINT

The JDBC type `SMALLINT` represents a 16-bit signed integer value between -32768 and 32767.

The corresponding SQL type, `SMALLINT`, is defined in SQL-92 and is supported by all the major databases. The SQL-92 standard leaves the precision of `SMALLINT` up to the implementation, but in practice, all the major databases support at least 16 bits.

The recommended Java mapping for the JDBC `SMALLINT` type is as a Java `short`.

### 8.3.6 INTEGER

The JDBC type `INTEGER` represents a a 32-bit signed integer value between - 2147483648 and 2147483647.

The corresponding SQL type, `INTEGER,` is defined in SQL-92 and is widely supported by all the major databases. The SQL-92 standard leaves the precision of `INTEGER` up to the implementation, but in practice all the major databases support at least 32 bits.

The recommended Java mapping for the `INTEGER` type is as a Java `int`.

### 8.3.7 BIGINT

The JDBC type `BIGINT` represents a 64-bit signed integer value between -9223372036854775808 and 9223372036854775807.

The corresponding SQL type `BIGINT` is a non-standard extension to SQL. In practice the SQL `BIGINT` type is not yet currently implemented by any of the major databases, and we recommend that its use should be avoided in portable code.

The recommended Java mapping for the `BIGINT` type is as a Java long.

### 8.3.8 REAL

The JDBC type `REAL` represents a "single precision" floating point number which supports 7 digits of mantissa.

The corresponding SQL type `REAL` is defined in SQL-92 and is widely, though not universally, supported by the major databases. The SQL-92 standard leaves the precision of `REAL` up to the implementation, but in practice all the major databases supporting `REAL` support a mantissa precision of at least 7 digits.

The recommended Java mapping for the `REAL` type is as a Java `float`.

### 8.3.9 DOUBLE

The JDBC type `DOUBLE` represents a "double precision" floating point number which supports 15 digits of mantissa.

The corresponding SQL type is `DOUBLE` `PRECISION,` which is defined in SQL- 92 and is widely supported by the major databases. The SQL-92 standard leaves the precision of `DOUBLE` `PRECISION` up to the implementation, but in practice all the major databases supporting `DOUBLE` `PRECISION` support a mantissa precision of at least 15 digits.

The recommended Java mapping for the `DOUBLE` type is as a Java `double`.

### 8.3.10 FLOAT

The JDBC type `FLOAT` is basically equivalent to the JDBC type `DOUBLE`. We provided both `FLOAT` and `DOUBLE` in a possibly misguided attempt at consistency with previous database APIs. `FLOAT` represents a "double precision" floating point number that supports 15 digits of mantissa.

The corresponding SQL type `FLOAT` is defined in SQL-92.`` The SQL-92 standard leaves the precision of `FLOAT` up to the implementation, but in practice all the major databases supporting `FLOAT` support a mantissa precision of at least 15 digits.

The recommended Java mapping for the `FLOAT` type is as a Java `double`. However, because of the potential confusion between the double precision SQL `FLOAT` and the single precision Java `float`, we recommend that JDBC programmers should normally use the JDBC `DOUBLE` type in preference to `FLOAT`.

### 8.3.11 DECIMAL and NUMERIC

The JDBC types `DECIMAL` and `NUMERIC` are very similar. They both represent fixed-precision decimal values.

The corresponding SQL types `DECIMAL` and `NUMERIC` are defined in SQL-92 and are very widely implemented. These SQL types takes precision and scale parameters. The precision is the total number of decimal digits supported, and the scale is the number of decimal digits after the decimal point. The scale must always be less than or equal to the precision. So for example, the value "12.345" has a precision of 5 and a scale of 3, and the value ".11" has a precision of 2 and a scale of 2. JDBC requires that all `DECIMAL` and `NUMERIC` types support both a precision and a scale of at least 15.

The sole distinction between `DECIMAL` and `NUMERIC` is that the SQL-92 specification requires that `NUMERIC` types be represented with exactly the specified precision, whereas for `DECIMAL` types, it allows an implementation to add additional precision beyond that specified when the type was created. Thus a column created with type `NUMERIC(12,4)` will always be represented with exactly 12 digits, whereas a column created with type `DECIMAL(12,4)` might be represented by some larger number of digits.

The recommended Java mapping for the `DECIMAL` and `NUMERIC` types is `java.math.BigDecimal`, a Java type that also expresses fixed-point numbers with absolute precision. The `java.math.BigDecimal` type provides math operations to allow `BigDecimal` types to be added, subtracted, multiplied, and divided with other `BigDecimal` types, with integer types, and with floating point types.

The method recommended for retrieving `DECIMAL` and `NUMERIC` values is `ResultSet.getBigDecimal`. JDBC also allows access to these SQL types as simple `Strings` or arrays of `char`. Thus, Java programmers can use `getString` to receive a `DECIMAL` or `NUMERIC` result. However, this makes the common case where `DECIMAL` or `NUMERIC` are used for currency values rather awkward, since it means that application writers have to perform math on strings. It is also possible to retrieve these SQL types as any of the Java numeric types.

### 8.3.12 DATE, TIME, and TIMESTAMP

There are three JDBC types relating to time:

- The JDBC `DATE` type represents a date consisting of day, month, and year. The corresponding SQL `DATE` type is defined in SQL-92, but it is implemented by only a subset of the major databases. Some databases offer alternative SQL types that support similar semantics.
- The JDBC `TIME` type represents a time consisting of hours, minutes, and seconds. The corresponding SQL `TIME` type is defined in SQL-92, but it is implemented by only a subset of the major databases. As with `DATE`, some databases offer alternative SQL types that support similar semantics
- The JDBC `TIMESTAMP` type represents `DATE` plus `TIME` plus a nanosecond field. The corresponding SQL `TIMESTAMP` type is defined in SQL-92, but it is implemented by only a very small number of databases.

Because the standard Java class `java.util.Date` does not match any of these three JDBC date-time types exactly (it includes both `DATE` and `TIME` information but has no nanoseconds), JDBC defines three subclasses of `java.util.Date` to correspond to the SQL types. They are:

- `java.sql.Date` for SQL `DATE` information. The hour, minute, second, and millisecond fields of the `java.util.Date` base class are set to zero.
- `java.sql.Time` for SQL `TIME` information. The year, month, and day fields of the `java.util.Date` base class are set to 1970, January, and 1. This is the "zero" date in the Java epoch.
- `java.sql.Timestamp` for SQL `TIMESTAMP` information. This class extends `java.util.Date` by adding a nanosecond field.

All three of the JDBC time-related classes are subclasses of `java.util.Date`, and as such, they can be used where a `java.util.Date` is expected. For example, internationalization methods take a `java.util.Date` object as an argument, so they can be passed instances of any of the JDBC time-related classes.

A JDBC `Timestamp` object has its parent's date and time components and also a separate nanoseconds component. If a `java.sql.Timestamp` object is used where a `java.util.Date` object is expected, the nanoseconds component is lost. However, since a j`ava.util.Date` object is stored with a precision of one millisecond, it is possible to maintain this degree of precision when converting a `java.sql.Timestamp` object to a `java.util.Date` object. This is done by converting the nanoseconds in the nanoseconds component to whole milliseconds (by dividing the number of nanoseconds by 1,000,000) and then adding the result to the `java.util.Date` object. Up to 999,999 nanoseconds may be lost in this conversion, but the resulting `java.util.Date` object will be accurate to within one millisecond.

The code fragment below is an example of converting a `java.sql.Timestamp` object to a `java.util.Date` object that is accurate to within one millisecond:

        Timestamp t = new Timestamp(100, 0, 1, 15, 45, 29, 987245732);
        java.util.Date d;
        d = new java.util.Date(t.getTime() + (t.getNanos() / 1000000));

## 8.4 Examples of Mapping

In any situation where a Java program retrieves data from a database, there has to be some form of mapping and data conversion. In most cases, JDBC programmers will be programming with knowledge of their target database's schema. They would know, for example, what tables the database contains and the data type for each column in those tables. They can therefore use the strongly-typed access methods in the interfaces `ResultSet`, `PreparedStatement`, and `CallableStatement`. This section presents three different scenarios, describing the data mapping and conversion required in each.

### 8.4.1 Simple SQL Statement

In the most common case, a user executes a simple SQL statement and gets back a `ResultSet` object with the results. The value returned by the database and stored in a `ResultSet` column will have a JDBC data type. A call to a `ResultSet.getXXX` method will retrieve that value as a Java data type. For example, if a `ResultSet` column contains a JDBC `FLOAT` value, the method `getDouble` will retrieve that value as a Java `double`. The table in Section 8.6.6 shows which `getXXX` methods may be used to retrieve which JDBC types. (A user who does not know the type of a `ResultSet` column can get that information by calling the method `ResultSet.getMetaData` and then invoking the `ResultSetMetaData` methods `getColumnType` or `getColumnTypeName`.) The following code fragment demonstrates getting the column type names for the columns in a result set:

        String query = "select * from Table1";
        ResultSet rs = stmt.executeQuery(query);
        ResultSetMetaData rsmd = rs.getMetaData();
        int columnCount = rsmd.getColumnCount();
        for (int i = 1; i <= columnCount; i++)  {
          String s = rsmd.getColumnTypeName(i);
          System.out.println ("Column " + i + " is type " + s);
        }

### 8.4.2 SQL Statement with IN Parameters

In another possible scenario, the user sends an SQL statement which takes input parameters. In this case, the user calls the `PreparedStatement.setXXX` methods to assign a value to each input parameter. For example, `PreparedStatement.setLong(1, 2345678)` will assign the value `2345678` to the first parameter as a Java `long`. The driver will convert `2345678` to a JDBC `BIGINT` in order to send it to the database. Which JDBC type the driver sends to the database is determined by the standard mapping from Java types to JDBC types, which is shown in the table in Section 8.6.2.

### 8.4.3 SQL Statement with INOUT Parameters

In yet another scenario, a user wants to call a stored procedure, assign values to its INOUT parameters, retrieve values from the results, and retrieve values from the parameters. This case is rather uncommon and more complicated than most, but it gives a good illustration of mapping and data conversion.

In this scenario, the first thing to do is to assign values to the INOUT parameters using `PreparedStatement.setXXX` methods. In addition, since the parameters will also be used for output, the programmer must register each parameter with the JDBC type of the value that the database will return to it. This is done with the method `CallableStatement.registerOutParameter`, which takes one of the JDBC types defined in the class `Types`. A programmer retrieves the results returned to a `ResultSet` object with `ResultSet.getXXX` methods and retrieves the values stored in the output parameters with `CallableStatement.getXXX` methods.

The `XXX` type used for `ResultSet`.`getXXX` methods is fairly flexible in some cases. The table in Section 8.6.6 shows which `ResultSet`.`getXXX` methods can be used to retrieve which JDBC types.

The `XXX` type used for `CallableStatement`.`getXXX` must map to the JDBC type registered for that parameter. For example, if the database is expected to return an output value whose type is `JDBC` `REAL`, the parameter should have been registered as `java.sql.Types.REAL`. Then to retrieve the `JDBC` `REAL` value, the method `CallableStatement.getFloat` should be called (the mapping from JDBC types to Java types is shown in the table in Section 8.6.1). The method `getFloat` will return the value stored in the output parameter after converting it from a JDBC `REAL` to a Java `float`. To accommodate various databases and make an application more portable, it is recommended that values be retrieved from `ResultSet` objects before values are retrieved from output parameters.

The following code demonstrates calling a stored procedure named `getTestData`, which has two parameters that are both INOUT parameters. First the `Connection` object `con` creates the `CallableStatement` object `cstmt`. Then the method `setByte` sets the first parameter to `25` as a Java `byte`. The driver will convert `25` to a JDBC `TINYINT` and send it to the database. The method `setBigDecimal` sets the second parameter with an input value of `83.75`. The driver will convert this `java.math.BigDecimal` object to a JDBC `NUMERIC` value. Next the two parameters are registered as OUT parameters, the first parameter as a JDBC `TINYINT` and the second parameter as a JDBC `DECIMAL` with two digits after the decimal point. After `cstmt` is executed, the values are retrieved from the `ResultSet` object using `ResultSet.getXXX` methods. The method `getString` gets the value in the first column as a Java `String` object, `getInt` gets the value in the second column as a Java `int`, and `getInt` gets the value in the third column as a Java `int`.

Then `CallableStatement.getXXX` methods retrieve the values stored in the output parameters. The method `getByte` retrieves the `JDBC` `TINYINT` as a Java `byte`, and `getBigDecimal` retrieves the `JDBC` `DECIMAL` as a `java.math.BigDecimal` object with two digits after the decimal point. Note that when a parameter is both an input and an output parameter, the `setXXX` method uses the same Java type as the `getXXX` method (as in `setByte` and `getByte`). The `registerOutParameter` method registers it to the JDBC type that is mapped from the Java type (a Java `byte` maps to a JDBC `TINYINT`, as shown in the table in Section 8.6.2).

        CallableStatement cstmt = con.prepareCall(
              "{call getTestData(?, ?)}");
        cstmt.setByte(1, 25);
        cstmt.setBigDecimal(2, 83.75);
        // register the first parameter as a JDBC TINYINT and the second
        //parameter as a JDBC DECIMAL with two digits after the decimal point
        cstmt.registerOutParameter(1, java.sql.Types.TINYINT);
        cstmt.registerOutParameter(2, java.sql.Types.DECIMAL, 2);
        ResultSet rs = cstmt.executeUpdate();
        // retrieve and print values in result set
        while(rs.next()) {
          String name = rs.getString(1);
          int score = rs.getInt(2);
          int percentile = rs.getInt(3);
          System.out.print("name = " + name + ", score = " + score + ", "
          System.out.println("percentile = " + percentile);
        // retrieve values in output parameters
        byte x = cstmt.getByte(1);
        java.math.BigDecimal n = cstmt.getBigDecimal(2, 2);

To generalize, the `XXX` in `CallableStatement.getXXX` and `PreparedStatement.setXXX` methods is a Java type. For `setXXX` methods, the driver converts the Java type to a JDBC type before sending it to the database (using the standard mappings shown in the table in Section 8.6.2). For `getXXX` methods, the driver converts the JDBC type returned by the database to a Java type (using the standard mappings shown in the table in Section 8.6.1) before returning it to the `getXXX` method.

The method `registerOutParameter` always takes a JDBC type as an argument, and the method `setObject` may take a JDBC type as an argument.

Note that if a JDBC type is supplied in its optional third argument, the method `setObject` will cause an explicit conversion of the parameter value from a Java type to the JDBC type specified. If no target JDBC type is supplied to `setObject`, the parameter value will be converted to the JDBC type that is the standard mapping from the Java type (as shown in Section 8.6.2). The driver will perform the explicit or implicit conversion before sending the parameter to the database.

## 8.5 Dynamic Data Access

In most cases, the user wants to access results or parameters whose data types are known at compile time. However, some applications, such as generic browsers or query tools, are compiled with no knowledge of the database schema they will access. For this reason, JDBC provides support for fully dynamically-typed data access in addition to static data type access.

Three methods and one constant facilitate accessing values whose data types are not known at compile time:

- `ResultSet.getObject`
- `PreparedStatement.setObject`
- `CallableStatement.getObject`
- `java.sql.Types.OTHER` (used as an argument to `CallableStatement.registerOutParameter`)

If, for example, an application wants to be able to accept a variety of types as results in a `ResultSet` object, it can use the method `ResultSet.getObject`.

The methods `ResultSet.getObject` and `CallableStatement.getObject` retrieve a value as a Java `Object`. Since `Object` is the base class for all Java objects, an instance of any Java class can be retrieved as an instance of `Object`. However, the following Java types are built-in "primitive" types and are therefore not instances of the class `Object`: `boolean`, `char`, `byte`, `short`, `int`, `long`, `float`, and `double`. As a result, these types cannot be retrieved by `getObject` methods. However, each of these primitive types has a corresponding class that serves as a wrapper. Instances of these classes are objects, which means that they can be retrieved with the methods `ResultSet.getObject` and `CallableStatement.getObject`. Table 8.6.3 on page 67 shows the mapping from a JDBC type to a Java `Object` type. This table differs from the standard mapping from JDBC type to Java type in that each primitive Java type is replaced by its wrapper class, except that JDBC `TINYINT` and JDBC `SMALLINT` are mapped to the Java class `Integer`.

The method `getObject` can also be used to retrieve user-defined Java types. With the advent of abstract data types (ADTs) or other user-defined types in some database systems, some vendors may find it convenient to use `getObject` for retrieving these types.

## 8.6 Tables for Data Type Mapping

This section contains the following tables relating to JDBC and Java data types:

Section 8.6.1-JDBC Types Mapped to Java Types

Section 8.6.2-Java Types Mapped to JDBC Types

Section 8.6.3-JDBC Types Mapped to Java `Object` Types

Section 8.6.4-Java `Object` Types Mapped to JDBC Types

Section 8.6.5- Conversions by `setObject`

Section 8.6.6-JDBC Types Retrieved by `ResultSet.getXXX` methods

### 8.6.1 JDBC Types Mapped to Java Types

JDBC type | Java type
--- | ---
`CHAR` | `String`
`VARCHAR` | `String`
`LONGVARCHAR` | `String`
`NUMERIC` | `java.math.BigDecimal`
`DECIMAL` | `java.math.BigDecimal`
`BIT` | `boolean`
`TINYINT` | `byte`
`SMALLINT` | `short`
`INTEGER` | `int`
`BIGINT` | `long`
`REAL` | `float`
`FLOAT` | `double`
`DOUBLE` | `double`
`BINARY` | `byte[]`
`VARBINARY` | `byte[]`
`LONGVARBINARY` | `byte[]`
`DATE` | `java.sql.Date`
`TIME` | `java.sql.Time`
`TIMESTAMP` | `java.sql.Timestamp`

### 8.6.2 Java Types Mapped to JDBC Types

This table shows the reverse mapping of Table 8.6.1, from Java types to JDBC types.

Java Type | JDBC type
--- | ---
`String` | `VARCHAR or LONGVARCHAR`
`java.math.BigDecimal` | `NUMERIC`
`boolean` | `BIT`
`byte` | `TINYINT`
`short` | `SMALLINT`
`int` | `INTEGER`
`long` | `BIGINT`
`float` | `REAL`
`double` | `DOUBLE`
`byte[]` | `VARBINARY or LONGVARBINARY`
`java.sql.Date` | `DATE`
`java.sql.Time` | `TIME`
`java.sql.Timestamp` | `TIMESTAMP`

The mapping for String will normally be `VARCHAR` but will turn into `LONGVARCHAR` if the given value exceeds the driver's limit on `VARCHAR` values. The same is true for `byte[]` and `VARBINARY` and `LONGVARBINARY` values.

### 8.6.3 JDBC Types Mapped to Java Object Types

Since the Java built-in types such as `boolean` and `int` are not subtypes of `Object`, there is a slightly different mapping from JDBC types to Java object types for the `getObject`/`setObject` methods. This mapping is shown in the following table:

JDBC Type | Java Object Type
--- | ---
`CHAR` | `String`
`VARCHAR` | `String`
`LONGVARCHAR` | `String`
`NUMERIC` | `java.math.BigDecimal`
`DECIMAL` | `java.math.BigDecimal`
`BIT` | `Boolean`
`TINYINT` | `Integer`
`SMALLINT` | `Integer`
`INTEGER` | `Integer`
`BIGINT` | `Long`
`REAL` | `Float`
`FLOAT` | `Double`
`DOUBLE` | `Double`
`BINARY` | `byte[]`
`VARBINARY` | `byte[]`
`LONGVARBINARY` | `byte[]`
`DATE` | `java.sql.Date`
`TIME` | `java.sql.Time`
`TIMESTAMP` | `java.sql.Timestamp`

### 8.6.4 Java Object Types Mapped to JDBC Types

Java Object Type | JDBC Type
--- | ---
`String` | `VARCHAR or LONGVARCHAR`
`java.math.BigDecimal` | `NUMERIC`
`Boolean` | `BIT`
`Integer` | `INTEGER`
`Long` | `BIGINT`
`Float` | `REAL`
`Double` | `DOUBLE`
`byte[]` | `VARBINARY or LONGVARBINARY`
`java.sql.Date` | `DATE`
`java.sql.Time` | `TIME`
`java.sql.Timestamp` | `TIMESTAMP`

Note that the mapping for `String` will normaly be `VARCHAR` but will turn into `LONGVARCHAR` if the given value exceeds the driver's limit on `VARCHAR` values. The case is similar for `byte[]` and `VARBINARY` and `LONGVARBINARY` values.

### 8.6.5 Conversions by setObject

The method `setObject` converts Java object types to JDBC types.

| T I N Y I N T | S M A L L I N T | I N T E G E R | B I G I N T | R E A L | F L O A T | D O U B L E | D E C I M A L | N U M E R I C | B I T | C H A R | V A R C H A R | L O N G V A R C H A R | B I N A R Y | V A R B I N A R Y | L O N G V A R B I N A R Y | D A T E | T I M E | T I M E S T A M P
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
String | x | x | x | x | x | x | x | x | x | x | x | x | x | x | x | x | x | x | x
java.math.BigDecimal | x | x | x | x | x | x | x | x | x | x | x | x | x |  |  |  |  |  |
Boolean | x | x | x | x | x | x | x | x | x | x | x | x | x |  |  |  |  |  |
Integer | x | x | x | x | x | x | x | x | x | x | x | x | x |  |  |  |  |  |
Long | x | x | x | x | x | x | x | x | x | x | x | x | x |  |  |  |  |  |
Float | x | x | x | x | x | x | x | x | x | x | x | x | x |  |  |  |  |  |
Double | x | x | x | x | x | x | x | x | x | x | x | x | x |  |  |  |  |  |
byte[] |  |  |  |  |  |  |  |  |  |  |  |  |  | x | x | x |  |  |
java.sql.Date |  |  |  |  |  |  |  |  |  |  | x | x | x |  |  |  | x |  | x
java.sql.Time |  |  |  |  |  |  |  |  |  |  | x | x | x |  |  |  |  | x |
java.sql.Time- stamp |  |  |  |  |  |  |  |  |  |  | x | x | x |  |  |  | x | x | x

Conversion from Java object types to JDBC types.

### 8.6.6 JDBC Types Retrieved by ResultSet.getXXX Methods

An "x" means that the method can retrieve the JDBC type. An "X" means that the method is recommended for the JDBC type.

| T I N Y I N T | S M A L L I N T | I N T E G E R | B I G I N T | R E A L | F L O A T | D O U B L E | D E C I M A L | N U M E R I C | B I T | C H A R | V A R C H A R | L O N G V A R C H A R | B I N A R Y | V A R B I N A R Y | L O N G V A R B I N A R Y | D A T E | T I M E | T I M E S T A M P
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
getByte | X | x | x | x | x | x | x | x | x | x | x | x | x |  |  |  |  |  |
getShort | x | X | x | x | x | x | x | x | x | x | x | x | x |  |  |  |  |  |
getInt | x | x | X | x | x | x | x | x | x | x | x | x | x |  |  |  |  |  |
getLong | x | x | x | X | x | x | x | x | x | x | x | x | x |  |  |  |  |  |
getFloat | x | x | x | x | X | x | x | x | x | x | x | x | x |  |  |  |  |  |
getDouble | x | x | x | x | x | X | X | x | x | x | x | x | x |  |  |  |  |  |
getBigDecimal | x | x | x | x | x | x | x | X | X | x | x | x | x |  |  |  |  |  |
getBoolean | x | x | x | x | x | x | x | x | x | X | x | x | x |  |  |  |  |  |
getString | x | x | x | x | x | x | x | x | x | x | X | X | x | x | x | x | x | x | x
getBytes |  |  |  |  |  |  |  |  |  |  |  |  |  | X | X | x |  |  |
getDate |  |  |  |  |  |  |  |  |  |  | x | x | x |  |  |  | X |  | x
getTime |  |  |  |  |  |  |  |  |  |  | x | x | x |  |  |  |  | X | x
getTimestamp |  |  |  |  |  |  |  |  |  |  | x | x | x |  |  |  | x |  | X
getAsciiStream |  |  |  |  |  |  |  |  |  |  | x | x | X | x | x | x |  |  |
getUnicodeStream |  |  |  |  |  |  |  |  |  |  | x | x | X | x | x | x |  |  |
getBinaryStream |  |  |  |  |  |  |  |  |  |  |  |  |  | x | x | X |  |  |
getObject | x | x | x | x | x | x | x | x | x | x | x | x | x | x | x | x | x | x | x

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