jsp - java.lang.IllegalStateException: Cannot forward after response has been committed in servletfilter -

i using filter determine whether or not requested page has valid session or not.

this code. web.xml:

    <filter>     <filter-name>sessionfilter</filter-name>     <filter-class>         com.imagemanagementutility.filter.sessionfilter     </filter-class>     <init-param>         <param-name>avoid-urls</param-name>         <param-value>index.jsp</param-value>     </init-param> </filter> <filter-mapping>     <filter-name>sessionfilter</filter-name>     <url-pattern>/*</url-pattern> </filter-mapping> 

filter class:

    public class sessionfilter implements filter {      private arraylist<string> urllist;      public void destroy() {     }      public void dofilter(servletrequest req, servletresponse res,             filterchain chain) throws ioexception, servletexception {          httpservletrequest request = (httpservletrequest) req;         httpservletresponse response = (httpservletresponse) res;         string url = request.getservletpath();         boolean allowedrequest = false;         system.out.println(url.replace("/",""));         if (urllist.contains(url)) {             allowedrequest = true;         }          if (!allowedrequest) {             httpsession session = request.getsession(false);             if (null == session) {                 system.out.println("redirect in servlet session filter");                 requestdispatcher dispatcher = request                         .getrequestdispatcher("//index.jsp");                 dispatcher.forward(request, response);             }         }              chain.dofilter(req, res);          system.out.println("end");     }      public void init(filterconfig config) throws servletexception {         string urls = config.getinitparameter("avoid-urls");         stringtokenizer token = new stringtokenizer(urls, ",");          urllist = new arraylist<string>();          while (token.hasmoretokens()) {             urllist.add(token.nexttoken());          }     } } 

i have login page used check whether or not user valid. if user valid control transfer servlet.

    public class mainservice extends httpservlet {     private static final long serialversionuid = 1l;     static logger log = logger.getlogger(mainservice.class.getname());      /**      * @see httpservlet#httpservlet()      */     public mainservice() {         super();     } /*      * @see httpservlet#doget(httpservletrequest request, httpservletresponse      *      response)      */     protected void doget(httpservletrequest request,             httpservletresponse response) throws servletexception, ioexception {      }      /**      * @see httpservlet#dopost(httpservletrequest request, httpservletresponse      *      response)      */     protected void dopost(httpservletrequest request,             httpservletresponse response) throws servletexception, ioexception {         httpsession session = request.getsession(true);         response.setcontenttype("text/html;charset=utf-8");         logutil.loginfo("i m here");         list<images> imagelist = null;         response.setcontenttype("text/html");         try {             userdataservice userdataservice = new userdataimpl();                string userid = null;             string username = null;             string password = null;             username = request.getparameter("user");             password = request.getparameter("password");              userid = userdataservice.checkuser(username, password);              if (userid!=null) {              system.out.println(userid);             session.setattribute("userid", userid);                  imagelist = userdataservice.getimages(userid);                 session.setattribute("imagelist", imagelist);               /*response.sendredirect("//showuserimages.jsp");*/                  requestdispatcher dispatcher = request                         .getrequestdispatcher("//showuserimages.jsp");                 dispatcher.forward(request, response);               } else {                  /*response.sendredirect("//index.jsp");*/                  requestdispatcher dispatcher = request                         .getrequestdispatcher("//index.jsp");                 dispatcher.forward(request, response);              }         } catch (imageexception e) {              e.getmessage();             e.printstacktrace();         }     }  } 

this works without filter, filter shows error when forward control "//showuserimages.jsp".

put invocation of dofilter in else block:

if (!allowedrequest) {     httpsession session = request.getsession(false);     if (null == session) {         system.out.println("redirect in servlet session filter");         requestdispatcher dispatcher = request                 .getrequestdispatcher("//index.jsp");         dispatcher.forward(request, response);     } }else{     chain.dofilter(req, res); }