Google App Engine Java Servlet读取JSP

Question

I am trying to have our servlets on Google App Engine Java, read the result of a JSP using the method here: Pass data from Java Servlet to JSP?

Specifically our code is

ByteArrayOutputStream bufferStream = new ByteArrayOutputStream();
ResponseWrapper responseWrapper = new ResponseWrapper(response, bufferStream);

getServletContext().getRequestDispatcher(jspUrl).forward(request, responseWrapper);**

responseWrapper.flushBuffer();
return bufferStream.toString();

However since we have sessions turned off in appengine-web.xml

<sessions-enabled>false</sessions-enabled>

we get the error below. Is there anyway for a servlet to read a JSP without GAE trying to add a session?

    com.google.apphosting.vmruntime.VmApiProxyDelegate convertApiResponseRpcErrorToException: Security violation: invalid request id used!
W 2014-10-16 12:16:19.004
    org.gails.util.server.TLogUtil logException: IndexServlet.readJspPage() /index.html
  java.lang.RuntimeException: Session support is not enabled in appengine-web.xml.  To enable sessions, put <sessions-enabled>true</sessions-enabled> in that file.  Without it, getSession() is allowed, but manipulation of sessionattributes is not.  Session support is not enabled in appengine-web.xml.  To enable sessions, put <sessions-enabled>true</sessions-enabled> in that file.  Without it, getSession() is allowed, but manipulation of sessionattributes is not.
    java.lang.RuntimeException: Session support is not enabled in appengine-web.xml.  To enable sessions, put <sessions-enabled>true</sessions-enabled> in that file.  Without it, getSession() is allowed, but manipulation of sessionattributes is not.
    at com.google.apphosting.utils.jetty9.StubSessionManager$StubSession.throwException(StubSessionManager.java:86)
    at com.google.apphosting.utils.jetty9.StubSessionManager$StubSession.setAttribute(StubSessionManager.java:74)
    at org.eclipse.jetty.security.SecurityHandler$1.sessionCreated(SecurityHandler.java:335)
    at org.eclipse.jetty.server.session.AbstractSessionManager.addSession(AbstractSessionManager.java:686)
    at org.eclipse.jetty.server.session.AbstractSessionManager.newHttpSession(AbstractSessionManager.java:566)
    at org.eclipse.jetty.server.Request.getSession(Request.java:1406)
    at org.eclipse.jetty.server.Request.getSession(Request.java:1379)
    at org.apache.jasper.runtime.PageContextImpl.initialize(PageContextImpl.java:134)
    at org.apache.jasper.runtime.JspFactoryImpl.internalGetPageContext(JspFactoryImpl.java:109)
    at org.apache.jasper.runtime.JspFactoryImpl.getPageContext(JspFactoryImpl.java:60)
    at org.apache.jsp._005ftradeos_jsp._jspService(_005ftradeos_jsp.java:100)
    at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:725)
    at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432)
    at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:405)
    at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:349)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:725)
    at org.eclipse.jetty.servlet.JspPropertyGroupServlet.service(JspPropertyGroupServlet.java:130)
    at org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:769)
    at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:585)
    at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:143)
    at org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:595)
    at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:223)
    at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1125)
    at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:515)
    at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:185)
    at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1059)
    at com.google.apphosting.vmruntime.jetty9.VmRuntimeWebAppContext.doScope(VmRuntimeWebAppContext.java:366)
    at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:141)
    at org.eclipse.jetty.server.Dispatcher.forward(Dispatcher.java:191)
    at org.eclipse.jetty.server.Dispatcher.forward(Dispatcher.java:72)
    at org.gails.site.server.IndexServlet.readJspPage(IndexServlet.java:279)

Answer 1

If you check the stack trace, the RequestDispatcher forward is triggering code that requires the use of sessions. The error message clearly tells you that you need to have <sessions-enabled>true</sessions-enabled> . The origin of this may be the fact that you get the RequestDispatcher from a call to getServletContext() , which if you check the javadoc, requires a session.

There may be other ways to get a RequestDispatcher to forward to a JSP, that don't create a session. Try to get the RequestDispatcher from the HttpServletRequest object with req.getRequestDispatcher() .

Either enable sessions, or at the very least, if the above advice didn't help and you still don't want to use sessions, you could try to use RequestDispatcher.include() , which might not require sessions(?), although again you would have to test.