Updating session items 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; public class UpdatingSessionItems extends HttpServlet { public void doGet( HttpServletRequest req, HttpServletResponse res ) throws ServletException, IOException { res.setContentType( "text/html" ); PrintWriter pw = res.getWriter(); pw.println( "" ); HttpSession theSession = req.getSession(); // updated a named item in the session synchronized( theSession ) { /** * when updating items within a session object, you must * ensure that you have exclusive access to session object * by first synchronizing on the session */ Integer counter = (Integer) theSession.getAttribute( "counter" ); if( counter == null ) { theSession.setAttribute( "counter", new Integer( 1 ) ); } else { theSession.setAttribute( "counter", new Integer( counter.intValue() + 1 ) ); } pw.println( "
" + counter ); /** * also note that items inside your session object should really * be serializable to ensure that your session can scale within * a clustered environment */ } pw.println( "" ); } }