How to Custom tags in jsp

[pratapsiva sivakumar]

Hello Sir,
I want to know how to write custom tags in jsp and how to define tld files and use them.I want complete explanation with an example code.

[Ulf Dittmer]

You're in luck - a good tutorial on tag libraries is available.

[Praneeth Thiruveedhula]

Hello Siva It is very easy to use the custom tags in jsp.

The main objective of custom tags is to completly remove the java code from the jsp.
the jstl,el,scriptlet.....etc may not completely remove the java code from the jsp.
by using custom tags we can remove the java code.

follow the bellow lines.

Required components to develop the custom tags.
1)TagHandler class.------>it is simple java class and it contains entire our own custom tag logic.
2)tld file------------------->it contains the mapping information b/w TagHandler class and the jsp file
3)jsp file with taglib directive.---> it is a simple jsp file contains your own custom tags.

ex for custom tag:--
<jrntr:iliyana/>
if this tag is encounterd by jsp engine internally tag handler class will be executed and the logic will be executed.
simple ex for custom tag:

test.jsp

<%@ taglib prefix="jrntr" uri="javamirchi" %>
<jrntr:iliyana/>

web.xml

<web-app>
<jsp-config>
<taglib>
<taglib-uri>javamirchi</taglib-uri>
<taglib-location>/WEB-INF/mytld.tld</taglib-location>
</taglib>
</jsp-config>
</web-app>

mytld.tld

<taglib version="2.0">
<tlib-version>1.0</tlib-version>
<tag>
<name>iliyana</name>
<tag-class>com.javamirchi.CustomTagDemo</tag-class>
</tag>
</taglib>

CustomTagDemo.java to compile this class you need to set the class path jsp-api.jar
here if you understand the code ok fine,otherwise just understand the flow of the application.

package com.javamirchi;
import javax.servlet.jsp.*;
import javax.servlet.jsp.tagext.*;
import java.io.*;
public class CustomTagDemo implements Tag
{
PageContext pcontext;
public void setPageContext(PageContext p)
{
pcontext=p;
}
public void setParent(Tag t)
{
}
public int doStartTag()throws JspException
{ try{
JspWriter out=pcontext.getOut();
out.println("<h1>hi guys NTR AND ILIYANA Combination is super<h1>");
}
catch(IOException e){}
return EVAL_BODY_INCLUDE;
}
public int doEndTag()throws JspException
{
return EVAL_PAGE;
}
public void release()
{}
public Tag getParent()
{
return null;
}
}

******used tomcat 5.5 version.(if you use tocat6 then change the <taglib version="2.1" > in mytld.tld file

folder structure
1)test.jsp----inside context root
2)mytld.tld---inside WEB-INF
3)web.xml---inside WEB-INF
4)CustomTagDemo--inside classes

flow of the above application.

*when ever the jsp engine encounters the custom tag it will find out the prefix.
*with this prefix it can find out the proper taglib directive.
*after that it will find out the uri.
*it takes that uri and directly goes to the web.xml in that we configured proper tld file.
*again it goes to tld file and find the logical name(here the logical name is iliyana <jrntr:iliyana/>)
*if it finds iliyana it can executes the corresponding TagHandlerClass.
*in that tag handler class what ever the logic is there that can be executes.

thats it cinima got completed.



cheers i hope you got some minimum idea about custom tags with this explanation.

By,
Praneeth.
JavaMirchi.

[Bear Bibeault]

Praneeth Thiruveedhula, please be sure to use code tags when posting code to the forums. Unformatted code is extremely hard to read. Please read this for more information.

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