Http client pull model

package com.ack.web.servlet;

import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

/**
 *
 * In this example, we demonstrate the client pull model.
 *
 * Here we have a client reading a book, specifying a
 * refresh every two seconds.  The current page is
 * stored in the client's HttpSession.
 *
 * When we have finished the book, we redirect the client
 * to the acknowledge web site
 *
 * Client Pull sees the client pulling content from the
 * server using the Refresh HTTP header directive
 */

public class HttpClientPullModel extends HttpServlet {

  public void doGet( HttpServletRequest req, HttpServletResponse res )
      throws ServletException, IOException {
    res.setContentType( "text/html" );
    PrintWriter pw = res.getWriter();

    // get a session to hold the current page
    HttpSession session = req.getSession();
    Integer pageNumber = (Integer) session.getAttribute( "page" );
    if( pageNumber == null ) {
      pageNumber = new Integer( 1 );
    }
    else {
      pageNumber = new Integer( pageNumber.intValue() + 1 );
    }
    pw.println( "Page: " + pageNumber );

    // finish the book when its gets to page 10
    if( pageNumber.intValue() == 10 ) {
      // tell client we're done and kill the session
      pw.println( "we are done reading.." );
      session.removeAttribute( "page" );
      session.invalidate();

      // finally, send the client to the client site after 5 secs
      res.setHeader( "Refresh", "5; URL=http://www.xxx" );
    }
    else {
      // if we have more pages, signal refresh of current page
      res.setHeader( "Refresh", "2" );
      session.setAttribute( "page", pageNumber );
    }

    // output some time information
    pw.println( "

---

" );
    pw.println( new java.util.Date( System.currentTimeMillis() ) );
  }
}