Question

I try to implement a servlet which should be called either through POST or GET.

So I wrote something like this

 @Override
 protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
  this.doGet(req, resp);
 }

 @Override
 protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
  // .. do stuff

  // forward to welcome page
  this.getServletContext().getRequestDispatcher("/guestbook.jsp").forward(req, resp);
  return;
 }

But/or because of the forward at the end I get an IllegalStateException, which is only a warning but still. What should I do differently?

Thanks,
-lony

Edit: Wanted Stacktrace

2012-05-26 18:02:16.422:WARN::/wsc/guestbook
java.lang.IllegalStateException: Committed
    at org.eclipse.jetty.server.Response.resetBuffer(Response.java:1056)
    at org.eclipse.jetty.server.Dispatcher.forward(Dispatcher.java:216)
    at org.eclipse.jetty.server.Dispatcher.forward(Dispatcher.java:115)
    at de.tum.in.dss.GuestbookController.doGet(GuestbookController.java:135)
    at de.tum.in.dss.GuestbookController.doPost(GuestbookController.java:37)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:820)
    at org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:538)
    at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1352)
    at de.tum.in.dss.XSSFilter.doFilter(XSSFilter.java:76)
    at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1323)
    at de.tum.in.dss.AccessFilter.doFilter(AccessFilter.java:55)
    at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1323)
    at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:476)
    at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:119)
    at org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:517)
    at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:225)
    at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:937)
    at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:406)
    at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:183)
    at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:871)
    at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:117)
    at org.eclipse.jetty.server.handler.ContextHandlerCollection.handle(ContextHandlerCollection.java:247)
    at org.eclipse.jetty.server.handler.HandlerCollection.handle(HandlerCollection.java:149)
    at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:110)
    at org.eclipse.jetty.server.Server.handle(Server.java:346)
    at org.eclipse.jetty.server.HttpConnection.handleRequest(HttpConnection.java:589)
    at org.eclipse.jetty.server.HttpConnection$RequestHandler.content(HttpConnection.java:1065)
    at org.eclipse.jetty.http.HttpParser.parseNext(HttpParser.java:823)
    at org.eclipse.jetty.http.HttpParser.parseAvailable(HttpParser.java:220)
    at org.eclipse.jetty.server.HttpConnection.handle(HttpConnection.java:411)
    at org.eclipse.jetty.io.nio.SelectChannelEndPoint.handle(SelectChannelEndPoint.java:535)
    at org.eclipse.jetty.io.nio.SelectChannelEndPoint$1.run(SelectChannelEndPoint.java:40)
    at org.eclipse.jetty.util.thread.QueuedThreadPool$3.run(QueuedThreadPool.java:529)
    at java.lang.Thread.run(Thread.java:722)

Answer 1

Your concrete problem is not related by letting GET and POST both do the same thing. Your problem is caused by writing to the response in the servlet and thus implicitly committing it before performing the forward.

Do not touch response.getWriter() or resposne.getOutputStream() in the servlet and just let JSP do that job. If you need to prepare data which JSP needs to display, just set it as an attribute in the request, session or application scope, depending on the scope the data needs to hold in.

See also:

• Our servlets wiki page

Doing the same job on GET and POST is by the way smelly. Are you sure you understand what exactly each of those methods are to be used for?