EL Variables, and Functions

Overview
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env tags
<resin>
<cluster>
<server>
port tags
<host>
<web-app>
<database>
session tags
rewrite tags
service tags
log
el variables
el control

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Examples

Servlet/Filter initialization

EL expressions can be used to configure servlets and filters. init-param 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 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:

Servlet using JDBC

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:

Example configuration

<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.

cluster

cluster properties
variable	meaning
id	The cluster id
root	The location of the content

Environment variables

Environment variables inherited by the process from the operting system are available as variables in el expressions, for example .

fmt.sprintf()

Format a string using a sprintf-like format string.

fmt.sprintf(format[,arg1, arg2 ... argN])

format	the format string (see below)	required
arg1..argN	the values used for the conversions in the format string	n/a

sprintf 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:

%[FLAGS][WIDTH][.PREC][TYPE]

TYPE is required, the rest are optional.

The following TYPE's are supported:

%%	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())

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:

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 <, > becomes > & becomes & ' becomes &#039, " becomes &034;

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.

fmt.timestamp()

Format a timestamp string.

fmt.timestamp(format[,date])

format	the format string (see below)	required
date	an object with java.util.Date or java.util.Calendar or com.caucho.util.QDate	the current date and time

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.

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)

host

host properties
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>

java

java properties
variable	meaning
version	The JDK version

jndi()

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

configuring JNDI

<servlet servlet-name='foo'
         servlet-class='qa.FooServlet'>
  <init>
    <data-source>${'${'}jndi:lookup("java:comp/env/jdbc/test")}</data-source>
  </init>
</servlet>

resin

resin properties
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

server

Values related to the active <server>.

server properties
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

System properties are available as variables in el expressions. Many system property names are not valid el identifiers; in that case the Var variable is used, for example .

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

Standard system properties
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

webApp

webApp properties
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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