JSP and JSTL Tutorials - Tutorial Addendum - JSP Custom Tag

What is a Custom Tag?

    

Custom Tag is an activity tag authentic by the user through the JSP tag addendum facility.

    

It can be acclimated to move JSP page assembly logics and advice into a tag Java class, and invoke

    

it by an activity tag that is affiliated to that class. There are two capital advantages of using

    

custom tags:

    

    
• Repeatable JSP page logics and advice can be simplified and centralized into a individual tag.
  
      

  For example, we can ascertain a custom tag alleged <my:copyright/> for bearing
  
      

  the absorb advice that charge to be acclimated on every page of server.
  
      



    
• Moving circuitous business logics from the JSP to a tag class, so the JSP page
  
      

  author can apply on the presentation logics only. For example, we can ascertain a
  
      

  custom tag alleged <my:userList/> for bearing a HTML table abounding with a account of users.
  
      

  The tag chic will administer how the put anniversary user into a row, and anniversary user acreage
  
      

  into a column.
  
      



    

I am abiding that the functionalities provided by custom tags can aswell be archived by

    

using JavaBean and scripting elements together. But tags assume to be simpler to use

    

for some artless JSP page authors.

    

"Hello world!" Custom Tag

    

Before we go into any abstruse details, let me use a actual simple archetype to appearance

    

you the accomplish to ascertain and use a custom tag.

    

I wish to ascertain a tag alleged <hy:hello/> to aftermath the "Hello world!" in the calling

    

JSP page.

    

1. Autograph the tag class. Actuality is my first tag class, HelloTag.java, which extends

    

the TagSupport chic provided in the JSP package:

    

 

    
/**

    
 * HelloTag.java

    
 * Absorb (c) 2003 by Dr.  Yang. All rights reserved.

    
 */

    
import java.io.*;

    
import javax.servlet.jsp.tagext.*;

    
public chic HelloTag extends TagSupport {

    
   accessible int doStartTag() {

    
      try {

    
         pageContext.getOut().write("Hello world!");

    
      } bolt (IOException e) {

    
         System.err.println(e.toString());

    
      }

    
      acknowledgment SKIP_BODY;

    
   }

    
}

    

2. Installing the tag class. I aggregate HelloTag.java with JDK 1.3.1, and servlet.jar

    

provided by the Bobcat 4.1.18 server. Like the JavaBean chic files, tag chic files

    

also charge to be installed in the chic aisle of the bobcat server. So I affected

    

the HelloTag.class to localjakarta-tomcat-4.1.18webapps
ootweb-infclasses directory.

    

(Continued on next part...)