Developing EL Functions 

Use

The EL enables you define your own functions to use in JSPs in your Web applications. You develop EL functions similarly to custom tags.

Procedure

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       1.      EL functions are mapped to public static methods in Java classes. To create an EL function, you create a Java file and implement your methods.

       2.      The implementation of the function must be available in the application classpath, thus you package the file under WEB-INF/classes. You can also bundle several classes in a JAR file. In this case you package the JAR under WEB-INF/lib.

       3.      To use the function in a JSP, you must first create a TLD and describe the function, for example myTLD.tld.

Starting with JSP 2.1, the TLDs you create must exactly follow the order of the elements as described in the TLD schema in the JSP 2.1 specification. The mandatory elements in a TLD are the taglib and short-name elements. Depending on the component you wish to use in your Web application, you also use a tag, tag-file, or function element respectively. We recommend that you also include the uri element. The order of elements defined in the schema is the following:

description

display-name

icon

tlib-version

short-name

uri

validator

listener

tag

tag-file

function

<taglib xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee

 http://java.sun.com/xml/ns/j2ee/web-jsptaglibrary_2_1.xsd version="2.1">

<short-name>my</short-name>

<uri>http://com.sap.docs/FunctionsTaglib</uri>

<function>

<name>myFunction</name>

<function-class>com.sap.demo.examples.myFunction</function-class>

<function-signature>java.lang.String myFunction(java.lang.String)</function-signature>

</function>

</taglib>

       4.      You import the TLD in the JSP page using the URI attribute of the taglib directive.

<%@taglib prefix=”my” uri=”http://com.sap.docs/FunctionsTaglib” %>

       5.      You use the function in your JSP using the prefix defined in the taglib directive.

You print a greeting to the current user:

${my:myFunction(user)}