guestbooktag.java

高级java2 大学教程(含源码,经典的Java学习教程

// Fig. 10.37: GuestBookTag.java
// Custom tag handler that reads information from the guestbook
// database and makes that data available in a JSP.
package com.deitel.advjhtp1.jsp.taglibrary;

// Java core packages
import java.io.*;
import java.util.*;

// Java extension packages
import javax.servlet.jsp.*;
import javax.servlet.jsp.tagext.*;

// Deitel packages
import com.deitel.advjhtp1.jsp.beans.*;

public class GuestBookTag extends BodyTagSupport {
   private String firstName;
   private String lastName;
   private String email;
   
   private GuestDataBean guestData;
   private GuestBean guest;
   private Iterator iterator;
   
   // Method called to begin tag processing
   public int doStartTag() throws JspException
   {
      // attempt tag processing
      try {
         guestData = new GuestDataBean();
         
         List list = guestData.getGuestList();
         iterator = list.iterator();
         
         if ( iterator.hasNext() ) {
            processNextGuest();
   
            return EVAL_BODY_TAG;    // continue body processing
         }
         else 
            return SKIP_BODY;     // terminate body processing
      }
      
      // if any exceptions occur, do not continue processing 
      // tag's body
      catch ( Exception exception ) {
         exception.printStackTrace();
         return SKIP_BODY;   // ignore the tag's body
      }
   }

   // process body and determine if body processing
   // should continue
   public int doAfterBody() 
   {
      // attempt to output body data
      try {
         bodyContent.writeOut( getPreviousOut() );
      } 

      // if exception occurs, terminate body processing
      catch ( IOException ioException ) {
         ioException.printStackTrace();
         return SKIP_BODY;  // terminate body processing
      }

      bodyContent.clearBody();
      
      if ( iterator.hasNext() ) {
         processNextGuest();

         return EVAL_BODY_TAG;    // continue body processing
      }
      else 
         return SKIP_BODY;     // terminate body processing
   }
   
   // obtains the next GuestBean and extracts its data
   private void processNextGuest()
   {
      // get next guest
      guest = ( GuestBean ) iterator.next();

      pageContext.setAttribute( 
         "firstName", guest.getFirstName() );

      pageContext.setAttribute( 
         "lastName", guest.getLastName() );

      pageContext.setAttribute( 
         "email", guest.getEmail() );      
   }
}

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 * (C) Copyright 2002 by Deitel & Associates, Inc. and         *
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