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14.1 The Components That Make Up a Tag Library

311

coreservlets.tags

 class and is called 

ExampleTag

. Thus, with Tomcat 3.1,

the class file would be in 

install_dir/webapps/ROOT/WEB INF/classes/core 

servlets/tags/ExampleTag.class

. 

Listing 14.1 ExampleTag.java 

package coreservlets.tags;

import javax.servlet.jsp.*;

import javax.servlet.jsp.tagext.*;

import java.io.*;

/** Very simple JSP tag that just inserts a string

 *  ("Custom tag example...") into the output.

 *  The actual name of the tag is not defined here;

 *  that is given by the Tag Library Descriptor (TLD)

 *  file that is referenced by the taglib directive

 *  in the JSP file.

 */

public class ExampleTag extends TagSupport {

  public int doStartTag() {

    try {

      JspWriter out = pageContext.getOut();

      out.print("Custom tag example " +

                "(coreservlets.tags.ExampleTag)");

    } catch(IOException ioe) {

      System.out.println("Error in ExampleTag: " + ioe);

    }

    return(SKIP_BODY);

  }

}

The Tag Library Descriptor File

Once you have defined a tag handler, your next task is to identify the class to

the server and to associate it with a particular XML tag name. This task is

accomplished by means of a tag library descriptor file (in XML format) like

the one shown in Listing 14.2. This file contains some fixed information, an

arbitrary short name for your library, a short description, and a series of tag

descriptions. The nonbold part of the listing is the same in virtually all tag

library descriptors and can be copied verbatim from the source code archive

at 

http://www.coreservlets.com/

 or from the Tomcat 3.1 standard exam 

ples (

install_dir/webapps/examples/WEB INF/jsp

). 

Second edition of this book: www.coreservlets.com; Sequel: www.moreservlets.com.

Servlet and JSP training courses by book's author: courses.coreservlets.com.