Illegal state exception in filters can any help me plzzzzzzz

Question

i want to check the clients status i mean whether the request is coming from new client or already using client , if clients request is new one then the filter has to redirect to some other login page and also if the request is asked to access the authenticated resource then also he want to force to redirect to login page.If the user is logged in and his session is not expired and if session is valid then he can access the requested url as per his role....can any one suggest the code plzzzzzzzzz
here is my code but iam getting the illegal state exception as shown below...
package uk.co.lex.interactive.authentication.action;
import java.io.IOException;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
public class AuthenticationFilter implements Filter {
private FilterConfig filterConfig=null;
HttpSession session=null;
     public void init(FilterConfig filterConfig) throws ServletException {
          //TODO Auto-generated method stub
          this.filterConfig=filterConfig;
          System.out.println("---Authentication filter initialized---");
     public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
          // TODO Auto-generated method stub
          HttpServletRequest req=(HttpServletRequest)request;
          HttpServletResponse res=(HttpServletResponse)response;
               String reqSessId=req.getRequestedSessionId();
          if(reqSessId!=null)
               {System.out.println("-------session is valid and the same client is using the resource111---");
                     if(req.isRequestedSessionIdValid())
                        System.out.println("-------session is valid and the same client is using the resource222---");
                        System.out.println("---requested sessid"+reqSessId);
                       if(req.isRequestedSessionIdFromCookie()||req.isRequestedSessionIdFromURL())
                            System.out.println("-------session is valid and the same client is using the resource333---");
          }else
          res.sendRedirect(req.getContextPath()+"/"+"checkUser.do");
                    System.out.println("------it is new session so it redirected to loginpage from authentication filter-------");
          else
               res.sendRedirect(req.getContextPath()+"/"+"checkUser.do");
               System.out.println("------it is new session so it redirected to loginpage from authentication filter-------");
          chain.doFilter(request,response);
     public void destroy() {
          // TODO Auto-generated method stub
          this.filterConfig=null;
          System.out.println("-----authentication filter destroyed---");
11:03:18,693 ERROR [[action]] Servlet.service() for servlet action threw exception
java.lang.IllegalStateException: Cannot create a session after the response has been committed
     at org.apache.catalina.connector.Request.doGetSession(Request.java:2195)
     at org.apache.catalina.connector.Request.getSession(Request.java:2017)
     at org.apache.catalina.connector.RequestFacade.getSession(RequestFacade.java:822)
     at org.apache.catalina.connector.RequestFacade.getSession(RequestFacade.java:833)
     at org.apache.struts.action.RequestProcessor.processLocale(RequestProcessor.java:621)
     at org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:177)
     at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1196)
     at org.apache.struts.action.ActionServlet.doGet(ActionServlet.java:414)
     at javax.servlet.http.HttpServlet.service(HttpServlet.java:697)
     at javax.servlet.http.HttpServlet.service(HttpServlet.java:810)
     at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:252)
     at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
     at uk.co.lex.interactive.authentication.action.AuthenticationFilter.doFilter(AuthenticationFilter.java:63)
     at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:202)
     at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
     at org.jboss.web.tomcat.filters.ReplyHeaderFilter.doFilter(ReplyHeaderFilter.java:81)
     at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:202)
     at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
     at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:213)
     at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:178)
     at org.jboss.web.tomcat.security.CustomPrincipalValve.invoke(CustomPrincipalValve.java:39)
     at org.jboss.web.tomcat.security.SecurityAssociationValve.invoke(SecurityAssociationValve.java:159)
     at org.jboss.web.tomcat.security.JaccContextValve.invoke(JaccContextValve.java:59)
     at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:126)
     at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:105)
     at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:107)
     at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:148)
     at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:856)
     at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.processConnection(Http11Protocol.java:744)
     at org.apache.tomcat.util.net.PoolTcpEndpoint.processSocket(PoolTcpEndpoint.java:527)
     at org.apache.tomcat.util.net.MasterSlaveWorkerThread.run(MasterSlaveWorkerThread.java:112)
     at java.lang.Thread.run(Thread.java:595)

Answer 1

I don't know that this is the root cause of your problem, but it certainly could be. When comparing two strings, you need to use the .equals() method, not ==.
(except in the null case, where checking for null with == is perfectly okay).
if (ViewProtectedPage.getValue("trycount").equals("1")
..etc
Some other notes... use if/else if/else rather than a whole bunch of ifs, since all your statements are mutually exclusive. Maybe even put those lower ifs inside your outer "else" since you're obviously not going to reach them after a sendRedirect(). On that same note, place a return; after the sendRedirect() to state that the rest of the page need not be loaded/executed.