Servlet counter 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; public class ServletCounter extends HttpServlet { private int instanceCount; private static int classCount; // process the HTTP get request public void doGet( HttpServletRequest request, HttpServletResponse response ) throws ServletException, IOException { response.setContentType( "text/html" ); PrintWriter out = new PrintWriter( response.getOutputStream() ); out.println( "" ); out.println( "ServletCounter" ); out.println( "" ); out.println( "

Hit the browser refresh button!
" ); out.println( "On 10, you'll get an exception, hit refresh again

" ); out.println( "

" ); // when you get to 10, throw exception to cause the // this servlet instance to be destroyed and reloaded if( instanceCount > 0 && ( instanceCount / 10 ) > 0 ) { instanceCount = 0; throw new ServletException( "Hit Refresh Again" ); } // synchronize on the servlet instance before updating the counter synchronized( this ) { // number of times this servlet instance has been accessed out.println( "
Servlet Instance Count -> " + instanceCount++ ); } // sychronize on the servlet class before updating the class-based counter synchronized( ServletCounter.class ) { // collective total of all accesses to all servlet instances created // by this class out.println( "
Servlet Total Request Count -> " + classCount++ ); } out.println( "" ); out.close(); } }