How we can use Servlet Filter for sessioncheck?

Question

I am new in java. am try to use Servlet filters for session check.My code is given below. but i got error while run. please help to correct the error. the 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 The server encountered an internal error that prevented it from fulfilling this request.

And my 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 My 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);
}
}

@Balusc that was not the answer for this question. just checkout this question and answer for it — Ajmal Muhammad, Jul 14 '15 at 11:39

score 1 · Answer 1 · answered Jul 14 '15 at 10:20

1

Problem is you had already redirected the user on login page for invalid session using response.sendRedirect("login"). However you had also tried to continue with request chain after redirect chain.doFilter(req, res).

Try using return keyword here:

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

answered Jul 14 '15 at 10:20

error change to 'This webpage has a redirect loop' – Ajmal Muhammad Jul 14 '15 at 10:27
@AjmalMuhammad Is this Only chrome behavior or IE/firefox also show similar behavior? – ring bearer Jul 14 '15 at 10:57
firefox shows this error "The page isn't redirecting properly Firefox has detected that the server is redirecting the request for this address in a way that will never complete. – Ajmal Muhammad Jul 14 '15 at 11:19
1

That's a different problem which is answered among others here: http://stackoverflow.com/questions/13114743/java-filter-infinite-loop/ – BalusC Jul 14 '15 at 11:34
thankyou BalusC it is working – Ajmal Muhammad Jul 14 '15 at 12:28

How we can use Servlet Filter for sessioncheck?

1 Answers1