The JSP Expression Language

Question

Developing and Using Functions
iam new to use the jsp ..
iam learning how to use taglib.
user defined functions
tell me steps to write user defined function using taglib
iam trying run the Code sample 3
in the given url..
http://java.sun.com/developer/technicalArticles/javaserverpages/JSP20/

Answer 1

Read this: http://java.sun.com/products/jsp/tutorial/TagLibrariesTOC.html
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To use these tags, you need to have 4 files:
1. Your .java file with the function ( the add() method in your case )
2. A .tld file, the taglib descriptor, to hold the 'function descriptor' as you call it. This maps the tag to the Java method
3. The web.xml, it has to have entries that tell the container ( Tomcat? ) where to find the TLD for a particular URI (http://jakarta.apache.org/tomcat/jsp2-example-taglib in your case )
4. The JSP page with the taglib directive as you've already made.
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How it works is:
1. the JSP page taglib directive tells the container that the prefix 'my' will refer to the taglib identified by the URI "http://jakarta.apache.org/tomcat/jsp2-example-taglib".
2. The container must now know which tag library is being referred to. The container, during startup, tracks all the entries in the web.xml and maps the URI with the location ( taglib-uri and taglib-location ).
3. The location points to your Java class: one.Compute
=======================================================
My doubt:
1)where i have to place the function descriptorThis is to be part of a .tld file, the taglib descriptor. Let's assume you save this TLD as myTaglib.tld and place it in /WEB-INF. Your entry will be like this:
<taglib xmlns="http://java.sun.com/xml/ns/j2ee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee
web-jsptaglibrary_2_0.xsd"
version="2.0">
<tlib-version>1.0</tlib-version>
<function>
        <description>add x and y</description>
        <name>add</name>
        <function-class>jsp2.examples.el.Compute
            </function-class>
        <function-signature>int
            add(java.lang.String,java.lang.String)
                </function-signature>
    </function>
</taglib>------------------------------------------------------------------------------------------------
2)<%@ taglib prefix="my"
ri="http://jakarta.apache.org/tomcat/jsp2-example-tagl
ib %>in the url just i have to mention that url else
anything i have to edit it.This is fine, as long as the URI value matches the taglib-uri element in your web.xml
You web.xml should have an entry :
<taglib>
<taglib-uri>
http://jakarta.apache.org/tomcat/jsp2-example-taglib
</taglib-uri>
<taglib-location>
/WEB-INF/myTaglib.tld
</taglib-location>
</taglib>
3)i had placed the compute .java program inside
package one is it necessary to place that program
in separate package else i can place it along other
java files.
) is i have to include any jar or TLD files in my
project ..All your loose classes ( .class files ) go into /WEB-INF/classes. They should be in folders representing the package heirarchy. So in your case, you've not declared the package in the code given. So I'm assuming you have
package one; in your .java file.
So your class should go into /WEB-INF/classes/one/Compute.class
All JARred classes ( in the form of .jar archives ) should be put into the /WEB-INF/lib folder.
The post is a bit messy but I think I've managed to get the basics right :)