java - How we can use Servlet Filter for sessioncheck? -

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• java.lang.illegalstateexception: cannot (forward | sendredirect | create session) after response has been committed 7 answers

i new in java. try use servlet filters session check.my code given below. got error while run. please correct error. error code is

 http status 500 - cannot forward after response has been committed type exception report  message cannot forward after response has been committed  description server encountered internal error prevented fulfilling request. 

and code is

my web.xml

    <servlet>             <servlet-name>login</servlet-name>             <servlet-class>com.sample.wordnik.servlet.loginservlet</servlet-class>         </servlet>         <welcome-file-list>             <welcome-file>index.html</welcome-file>         </welcome-file-list>         <servlet-mapping>         <servlet-name>login</servlet-name>         <url-pattern>/login</url-pattern>     </servlet-mapping> <filter>         <filter-name>sessionfilter</filter-name>         <filter-class>             com.sample.wordnik.filter.sessionfilter         </filter-class>         <init-param>             <param-name>avoid-urls</param-name>             <param-value>login.jsp,signup.jsp</param-value>          </init-param>     </filter>     <filter-mapping>         <filter-name>sessionfilter</filter-name>         <url-pattern>/*</url-pattern>     </filter-mapping> </web-app> 

my filter class is

import java.io.ioexception; import java.util.arraylist; import java.util.stringtokenizer; 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 sessionfilter implements filter {      private arraylist<string> urllist;      @override     public void destroy() {     }      @override     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;          if(urllist.contains(url)) {             allowedrequest = true;         }          if (!allowedrequest) {             httpsession session = request.getsession(false);             if (null == session) {                 response.sendredirect("login");             }         }          chain.dofilter(req, res);     }      @override     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());          }     } }  

and loginservlet is

public class loginservlet extends httpservlet {      @override     public void doget(httpservletrequest request, httpservletresponse response)             throws servletexception, ioexception { request.getrequestdispatcher("/web-inf/jsp/login.jsp").forward(request, response); } } 

problem had redirected user on login page invalid session using response.sendredirect("login"). had tried continue request chain after redirect chain.dofilter(req, res).

try using return keyword here:

if (null == session) {     response.sendredirect("login");     return; // added }