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EL expressions can be used to configure servlets and filters. values can use JSP EL expressions, including the ability to use system properties.

Servlets, filters, and resources can be configured like beans with setter methods are called directly (See Bean-style init).

One example use for the bean-style servlet initialization is to avoid JNDI lookup inside the servlet code. For example, a servlet that that uses a JDBC DataSource might look like:

package test; ... public class TestServlet extends HttpServlet { private DataSource _dataSource; /** * Bean setter is called to configure the servlet * before the init() method. */ public void setDataSource(DataSource dataSource) { _dataSource = dataSource; } ... }

The servlet is configured as follows:

<web-app> <allow-servlet-el/> <servlet servlet-name='test' servlet-class='test.TestServlet'> <init> <data-source>${jndi("java:comp/env/jdbc/test")}</data-source> </init> </servlet> ... </web-app>

The `<data-source>` xml tag corresponds to the `setDataSource` method of the bean. More infomation on this powerful pattern is in the bean configuration section of the documentation.

Environment variables inherited by the process from the operting system are available as variables in el expressions, for example `${LANG}`.

Format a string using a sprintf-like format string.

<def>fmt.sprintf(format[,arg1, arg2 ... argN])</def>
format the format string (see below) required
arg1..argN the values used for the conversions in the format string n/a

`` accepts a series of arguments, applies to each a format specifier from `format', and returns the formatted data as a string. `format' is a string containing two types of objects: ordinary characters (other than `%'), which are copied unchanged to the output, and conversion specifications, each of which is introduced by `%'. (To include `%' in the output, use `%%' in the format string).

A conversion specification has the following form:

<def>%[FLAGS][WIDTH][.PREC][TYPE]</def>

TYPE is required, the rest are optional.

The following TYPE's are supported:

<deftable>
%% a percent sign
%c a character with the given number
%s a string, a null string becomes "#null"
%z a string, a null string becomes the empty string ""
%d a signed integer, in decimal
%o an integer, in octal
%u an integer, in decimal
%x an integer, in hexadecimal
%X an integer, in hexadecimal using upper-case letters
%e a floating-point number, in scientific notation
%E a floating-point number, like %e with an upper-case "E"
%f a floating-point number, in fixed decimal notation
%g a floating-point number, in %e or %f notation
%G a floating-point number, like %g with an upper-case "E"
%p a pointer (outputs a value like the default of toString())
</deftable>

Intepret the word `integer' to mean the java type long. Since java does not support unsigned integers, all integers are treated the same.

The following optional FLAGS are supported:

<deftable>
0 If the TYPE character is an integer leading zeroes are used to pad the field width instead of spaces (following any indication of sign or base).
+ Include a `+' with positive numbers.
(a space) use a space placeholder for the `+' that would result from a positive number
- The result of is left justified, and the right is padded with blanks until the result is `WIDTH' in length. If you do not use this flag, the result is right justified, and padded on the left.
# an alternate display is used, for `x' and `X' a non-zero result will have an "0x" prefix; for floating point numbers the result will always contain a decimal point.
j escape a string suitable for a Java string, or a CSV file. The following escapes are applied: " becomes \", newline becomes \n, return becomes \r, \ becomes \\.
v escape a string suitable for CSV files, the same as `j' with an additional `"` placed at the beginning and ending of the string
m escape a string suitable for a XML file. The following escapes are applied: < becomes &lt;, > becomes &gt; & becomes &amp; ' becomes &#039, " becomes &034;
</deftable>

The optional WIDTH argument specifies a minium width for the field. Spaces are used unless the `0' FLAG was used to indicate 0 padding.

The optional PREC argument is introduced with a `.', and gives the maximum number of characters to print; or the minimum number of digits to print for integer and hex values; or the maximum number of significant digits for `g' and `G'; or the number of digits to print after the decimal point for floating points.

Format a timestamp string.

<example>fmt.timestamp(format[,date])
format the format string (see below) required
date an object with or or the current date and time
<example> msg="The current date and time is ${fmt.timestamp('%Y/%m/%d %H:%M:%S.%s')}" msg="time=${fmt.timestamp('[%Y/%m/%d %H:%M:%S.%s]')}"

`format` contains regular characters, which are just copied to the output string, and percent codes which are substituted with time and date values.

<deftable>
Code Meaning
%a day of week (short)
%A day of week (verbose)
%b day of month (short)
%B day of month (verbose)
%c Java locale date
%d day of month (two-digit)
%H 24-hour (two-digit)
%I 12-hour (two-digit)
%j day of year (three-digit)
%m month (two-digit)
%M minutes
%p am/pm
%S seconds
%s milliseconds
%W week in year (three-digit)
%w day of week (one-digit)
%y year (two-digit)
%Y year (four-digit)
%Z time zone (name)
%z time zone (+/-0800)
</deftable>
variable meaning
name The name of the host
regexp Regular expression values for host regexp matches
root The root directory of the host
url The canonical url of the host
<example> <host regexp="www.([^.]+).com"> <root-directory>/opt/www/${host.regexp[1]}</root-directory> <context-param server-id="${server.name}"/> <web-app id="/"> <document-directory>webapps/ROOT</document-directory> </web-app> </host>
variable meaning
version The JDK version

The configuration EL supports the static function jndi:lookup. jndi:lookup can be used to lookup a JNDI value for the configuration.

<servlet servlet-name='foo' servlet-class='qa.FooServlet'> <init> <data-source>${jndi:lookup("java:comp/env/jdbc/test")}</data-source> </init> </servlet>
variable meaning
address The local IP address
conf Path to the configuration file
home The the location of the Resin executables
hostName The local hostname as returned by InetAddress
root The location of the content, specified at startup with --resin-root
serverId The identity of the active <server>, specified at startup with --server
version The resin version, e.g. 3.1.0

Values related to the active <server>.

variable meaning
address the bind address of the cluster and load balancing port
id The identity of the active <server>, specified at startup with --server
port the cluster and load balancing port
httpAddress the bind address of the http listener, INADDR_ANY for all addresses
httpPort the port number of the http listener
httpsAddress the bind address of the ssl http listener, INADDR_ANY for all addresses
httpsPort the port number of the ssl http listener

System properties are available as variables in el expressions. Many system property names are not valid el identifiers; in that case the system variable is used, for example `${system['java.io.tmpdir']}`.

A full list of standard java system properties is provided in the javadoc for java.lang.System.

variable meaning
java.io.tmpdir Default temp file path
os.name Operating system name
os.arch Operating system architecture
os.version Operating system version
user.name User's account name
user.home User's home directory
user.dir User's current working directory
variable meaning
name The name of the web-app
contextPath The context path of the web-app
regexp Regular expression values for web-app regexp matches
root The root directory of the web-app
url The canonical url of the web app
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