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Custom Tag example with no attribute and no body

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This example demonstrates how one can make custom tag in JSP that has no attribute and no body.

Custom Tag example with no attribute and no body

     

Example program to demonstrate how to make custom tag with no attribute and no body

This example demonstrates how one can make custom tag in JSP that has no attribute and no body. There are only handful of tags in JSP which may not be sufficient for each and every working. You may require to make custom tags which will work according to user requirement. This functionality can be achieved by making a customized tag. For making a customized tag you have to implement Tag interface and you are required to override following methods in your tag class. These are as follows:

  1. doStartTag()
  2. doEndTag()
  3. release()
  4. setPageContext()
  5. setParent()
  6. getParent()

If the TagLibraryDesciptor indicates that tag must always have an empty action by the entry in ".tld" file as <bodycontent> entry of "empty", then doStartTag() method must return SKIP_BODY. Otherwise it may return EVAL_BODY_INCLUDE.

If SKIP_BODY is returned by doStartTag() then if body is present then it is not evaluated. If EVAL_BODY_INCLUDE is returned, the body is evaluated and "passed through" to the current output.

1. emptyTag.java

package mytag;

import java.io.*;
import javax.servlet.*;
import javax.servlet.jsp.*;
import javax.servlet.jsp.tagext.*;
import java.util.*;

public class emptyTag implements Tag {
 private PageContext pageContext;
 private Tag parent;
 
 public emptyTag() {
  super();
 }

 public int doStartTag() throws JspException {
  try {
 pageContext.getOut().print("This is an empty tag!");
  catch (IOException ioe) {
 throw new JspException("Error:"+ioe.getMessage());
  }
  return SKIP_BODY;
 }

 public int doEndTag() throws JspException {
  return SKIP_PAGE;
 }
 public void release() {
 }

 public void setPageContext(PageContext pageContext) {
  this.pageContext = pageContext;
 }

 public void setParent(Tag parent) {
  this.parent = parent;
 }

 public Tag getParent() {
  return parent;
 }

}

In this emptyTag.java doStartTag() will print "This is an empty tag!" wherever <custom:empty> would be used it will print this line and rest content of body is ignored. To use customized tag you have to make "taglib.tld" file and have to do following entries:

2. taglib.tld

<?xml version="1.0" encoding="ISO-8859-1" ?>
<!DOCTYPE taglib PUBLIC "-//Sun Microsystems, Inc.//DTD JSP Tag 
Library 1.2//EN"
"http://java.sun.com/dtd/web-jsptaglibrary_1_2.dtd">
<taglib>
  <tlibversion>1.0</tlibversion>
  <jspversion>1.1</jspversion>
  <shortname>custom</shortname>
  <tag>
  <name>empty</name>
  <tagclass>mytag.emptyTag</tagclass>
  <bodycontent>empty</bodycontent>
  <info>Tag having no attribute and no body</info>
   </tag>
</taglib>

To use tag in JSP page you have to write this line:

<%@ taglib uri="/WEB-INF/taglib.tld" prefix="custom" %>

Full code of JSP page is as follows:

3. CustomTag.jsp

<%@ taglib uri="/WEB-INF/taglib.tld" prefix="custom" %>
<html>
<head>
<title>Custom Tag with no attribute</title>
</head>
   <body bgcolor="ffffcc">
   <H1>Welocome ! </H1>
  Custom tag work starts...
   <custom:empty/>
  Custom tag work ends...
  Body Content of JSP page 
   </body>
</html>

Create and save these above files and start tomcat server. After executing this JSP file you will get output like this:

Output:

Download Source code

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Posted on: July 5, 2008

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