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330

Chapter 14 Creating Custom JSP Tag Libraries

_jspService

, 

doGet

, and 

doPost

. The solution to this dilemma is to use

getRequest

 to obtain the 

HttpServletRequest

 from the automatically

defined 

pageContext

 field of 

TagSupport

. Strictly speaking, the return

type of 

getRequest

 is 

ServletRequest

, so you have to do a typecast to

HttpServletRequest

 if you want to call a method that is not inherited

from 

ServletRequest

. However, in this case I just use 

getParameter

, so

no typecast is required.

Listing 14.13 defines a tag that ignores its body unless a request time

debug

 parameter is supplied. Such a tag provides a useful capability whereby

you embed debugging information directly in the JSP page during develop 

ment, but activate it only when a problem occurs. 

Listing 14.13 DebugTag.java 

package coreservlets.tags;

import javax.servlet.jsp.*;

import javax.servlet.jsp.tagext.*;

import java.io.*;

import javax.servlet.*;

/** A tag that includes the body content only if

 *  the "debug" request parameter is set.

 */

public class DebugTag extends TagSupport {

  public int doStartTag() {

    ServletRequest request = pageContext.getRequest();

    String debugFlag = request.getParameter("debug");

    if ((debugFlag != null) &&

        (!debugFlag.equalsIgnoreCase("false"))) {

      return(EVAL_BODY_INCLUDE);

    } else {

      return(SKIP_BODY);

    }

  }

}

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