NPE in SeamResourceServlet for delivering XML

[mobazr]

Hi,

I'm working on a class in order to deploy it as a SeamResourceServlet. It will be used to provide flash with xml data by receiving xml from the request, computing it and writing the manipulated xml back to the response.

@Scope(ScopeType.APPLICATION)
@Name("flashCommunicationResource")
public class FlashCommunicationResource extends AbstractResource {

        //
        // attributes
        //
        @Logger
        private static Log logger;

        @In(create = true, required = false)
        private FlashController flashController;


        @Override
        public String getResourcePath() {
                return "/myresource";
        }

        @Override
        public void getResource(final HttpServletRequest request, final HttpServletResponse response)
                        throws ServletException, IOException {

                new ContextualHttpServletRequest(request) {
                        @Override
                        public void process() throws IOException {
                                doWork(request, response);
                        }
                }.run();
        }

        private void doWork(HttpServletRequest request, HttpServletResponse response) {

                InputStream instream = null;
                OutputStream outstream = null;
                try {
                        instream = request.getInputStream();
                        response.setContentType("text/xml");
                        outstream = response.getOutputStream();

                        logger.debug("type=" + type);
                        flashController.computeXmlInputAndWriteResult(instream, outstream);

                        outstream.flush();
                        outstream.close();
                        instream.close();
                }
                catch (IOException e) {
                        ...
                }
        }
}

I checked the outstream by diverting it to System.out which looks perfect. But Seam crashes with the following NPE:

java.lang.NullPointerException
        at org.jboss.seam.contexts.Contexts.destroy(Contexts.java:241)
        at org.jboss.seam.contexts.Lifecycle.endCall(Lifecycle.java:95)
        at org.jboss.seam.intercept.RootInterceptor.invoke(RootInterceptor.java:122)
        at org.jboss.seam.intercept.JavaBeanInterceptor.interceptInvocation(JavaBeanInterceptor.java:166)
        at org.jboss.seam.intercept.JavaBeanInterceptor.invoke(JavaBeanInterceptor.java:102)
        at ....FlashCommunicationResource_$$_javassist_1.getResource(FlashCommunicationResource_$$_javassist_1.java)
        at org.jboss.seam.servlet.SeamResourceServlet.service(SeamResourceServlet.java:80)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
        ....

I'm fairly new to seam. Any ideas?
Thanks allot in advance.
Manuel

[mobazr]

Sorry for the weird looking code. Here it is reformatted:

@Scope(ScopeType.APPLICATION) 
@Name("flashCommunicationResource") 
public class FlashCommunicationResource extends AbstractResource { 

     @Logger private static Log logger; 

     @In(create = true, required = false) 
     private FlashController flashController; 

     @Override 
     public String getResourcePath() { return "/myresource"; } 

     @Override public void getResource(final HttpServletRequest request, final HttpServletResponse response) throws ServletException, IOException { 

          new ContextualHttpServletRequest(request) 
          { 
               @Override public void process() throws IOException { 
                    doWork(request, response); } 
          }.run(); 
     } 

     private void doWork(HttpServletRequest request, HttpServletResponse response) { 
          InputStream instream = null; 
          OutputStream outstream = null; 
          try { 
               instream = request.getInputStream(); 
               response.setContentType("text/xml"); 
               outstream = response.getOutputStream(); 
               
               flashController.computeXmlInputAndWriteResult(instream, outstream); 
               outstream.flush(); 
               outstream.close(); 
               instream.close(); 
          } catch (IOException e) { ... } 
     }
}

java.lang.NullPointerException 
at org.jboss.seam.contexts.Contexts.destroy(Contexts.java:241) 
at org.jboss.seam.contexts.Lifecycle.endCall(Lifecycle.java:95) 
at org.jboss.seam.intercept.RootInterceptor.invoke(RootInterceptor.java:122) 
at org.jboss.seam.intercept.JavaBeanInterceptor.interceptInvocation(JavaBeanInterceptor.java:166) 
at org.jboss.seam.intercept.JavaBeanInterceptor.invoke(JavaBeanInterceptor.java:102) 
at ....FlashCommunicationResource_$$_javassist_1.getResource(FlashCommunicationResource_$$_javassist_1.java) 
at org.jboss.seam.servlet.SeamResourceServlet.service(SeamResourceServlet.java:80) 
at javax.servlet.http.HttpServlet.service(HttpServlet.java:803) 
....

[shane.bryzak]

Are you sure the request is not already wrapped by the ContextFilter ?

[mobazr]

I'm new to seam, so I'm not quite sure what you mean. I found this page (here) and thought I adapated the code shown correctly. Might there be something wrong with my code?

I checked the web.xml and the Seam ContextFilter was not configured yet. I configured it in the web.xml with the url-pattern '/seam/resource/*' and now get the following exception:

09:05:36,602 WARN  [ContextualHttpServletRequest] ended request due to exception
java.lang.IllegalStateException: No active event context
     at org.jboss.seam.core.Manager.instance(Manager.java:272)
     at org.jboss.seam.servlet.ContextualHttpServletRequest.run(ContextualHttpServletRequest.java:55)
     at org.jboss.seam.web.ContextFilter.doFilter(ContextFilter.java:37)
     at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
     at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
     at org.jboss.seam.servlet.SeamFilter$FilterChainImpl.doFilter(SeamFilter.java:83)
     at org.jboss.seam.debug.hot.HotDeployFilter.doFilter(HotDeployFilter.java:51)
        ...

Any help or idea is much appreciated.

[shane.bryzak]

Do you already have org.jboss.seam.servlet.SeamFilter configured in web.xml?  If so, you don't need to configure ContextFilter explicitly.  I recommend that you try removing the ContextualHttpRequest wrapper from your resource code.

[shane.bryzak]

Oops, I mean ContextualHttpServletRequest.

[mobazr]

Yes, the Seam Filter is configured to filter all requests (/*). I removed wrapping the request in a ContextualHttpServletRequest and the NPE was solved. Btw: The original request is of the type org.jboss.seam.web.IdentityRequestWrapper.

Apparently now the request seems not to be part of the seam context. Within my flashController I have a user object injected which gets initialized with each session start. The class that performs the initalization is annotated with

 @Scope(ScopeType.SESSION)
 @Startup

and outjects the user object into the session. From the log I can tell that it is definatly called. So the user objects must exist. It seems that my request is not part of the seam context because I get a

@In attribute requires non-null value

Any ideas?

[shane.bryzak]

It should be easy enough to tell if the Seam contexts have been initialized for your request - using a debugger, set a breakpoint in your method and then see if Contexts.getSessionContext() returns a value.

[mobazr]

If I wrap the request into the ContextualHttpServletRequest I have the same SessionContext object available in the class that creates/outjects my user object and within the FlashController class. So I assume wrapping the request tells Seam to use the same context. 

If I remove wrapping the request there is only a BasicContext available in the FlashController and thus the user object is not injected. Which makes sense as the context is not the same.

Is there a way to tell seam that the normal/not wrapped request should run in the same SessionContext? Or do you see another solution for the NPE within the wrapped request?

Thanks so far.

[kukeltje.ronald.jbpm.org]

Shane Bryzak wrote on Nov 11, 2008 10:17:


Do you already have org.jboss.seam.servlet.SeamFilter configured in web.xml?  If so, you don't need to configure ContextFilter explicitly.

TTTTTTTHHHHHHHHHHHHHHHHAAAAAAAAAAAAAAANNNNNNNNNNKKKKKKKKKKKKKSSSSSSSSSSSSSS

This was a left-over in my components.xml for trying to get a custom servletfilter to work with seam (so an xforms engine can be used in seam) The 'no event context' error does not occur if you are in .seam pages. Only if you use custom pages (.xform) you get this error...

[mobazr]

I've already tried that before. When I add the @BypassInterceptors annotation into my resource the Seam Component flashController is not injected. Which in a way makes sense because the api already explains that the annotation will disable interception of calls to that seam component (here my resource).

Do I need to instantiate the FlashController myself? That doesn't really sound right to me, because I hoped that was something seam would do for me. Or do I need to declare which type/methods it should bypass and which not? And if so, which should I add?

Any ideas? Thanks allot.

Manuel

[kukeltje.ronald.jbpm.org]

The following works for me. The additional helper is needed with application scope, as is @BypassInterceptors on the filter.

my filter:

@Startup
@Scope(ScopeType.APPLICATION)
@Name("org.domain.TestFilter")
@BypassInterceptors
@Filter(within = "org.jboss.seam.web.ajax4jsfFilter")
public class TestFilter extends AbstractFilter {

    @Logger
    private Log log;

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
     super.init(filterConfig);
    }

    @Destroy
    public void destroy() {
     log.debug("cleanups allocated resources");
    }

    public void doFilter(final ServletRequest servletRequest,
         final ServletResponse servletResponse, final FilterChain filterChain)
         throws IOException, ServletException {

     // make extension configurable
     String requestURL = ((HttpServletRequest) servletRequest).getRequestURL().toString(); 
     if (requestURL.endsWith(".xform")) {
         new ContextualHttpServletRequest(
              (HttpServletRequest) servletRequest) {

          @Override
          public void process() throws Exception {

              log.debug("Processing #0, requestURL);
              processRequest(servletRequest, servletResponse, filterChain);
              log.debug("Processed #0", requestURL);

              filterChain.doFilter(servletRequest, servletResponse);
          }

         }.run();

         
         
     } else {
         log.debug("Ignoring #0", requestURL);
         filterChain.doFilter(servletRequest, servletResponse);
     }
     
     
    }

    private void processRequest(ServletRequest servletRequest,
         ServletResponse servletResponse, FilterChain filterChain)
         throws IOException, ServletException {


     TestFilterHelper tfh = (TestFilterHelper) Component
          .getInstance("org.domain.TestFilterHelper");

     tfh.handleSomething(servletRequest, servletResponse, filterChain);
    }
}

My helper:

@Name("org.domain.TestFilterHelper")
// Application scope is needed
@Scope(ScopeType.APPLICATION)
public class TestFilterHelper {

    @Logger
    Log log;

    // cannot have create=true
    @In(scope = ScopeType.CONVERSATION, value = "org.domain.NeededClass", required = false)
    NeededClass neededClass;

    @Create
    public void onCreate() {
     log.info("TestFilterHelper created");

    }

    public void handleSomething(ServletRequest servletRequest,
         ServletResponse servletResponse, FilterChain filterChain)
         throws IOException, ServletException {

     log.info("handleSomething(..,..,..)");
     if (neededClass == null) {
         log.info("neededClass == null, checking conversationId");

         if (ConversationPropagation.instance().getConversationId() != null
              && Contexts.isConversationContextActive()) {

          log.debug("There is a long running conversation... getting context and creating instance of component');
          neededClass = (NeededClass) Component.getInstance(
               "org.domain.NeededClass",
               ScopeType.CONVERSATION);
          log.debug("neededClass: #0", neededClass);

         } else {
          log.debug("Silently ignoring the fact that there is no long conversationid");
          return;
         }

     } else {
         log.info("We have an existing XFormsSession: #0", neededClass);
     }

     neededClass.handleRequest();
    }

my 'NeededClass':

@AutoCreate
@Name("org.domain.NeededClass")
@Scope(ScopeType.CONVERSATION)
public class NeededClass implements Serializable {

    private static final long serialVersionUID = 7610455116364472374L;
    
    @Logger
    Log log;

    public synchronized void handleRequest() throws IOException {

     log.info("Start handleRequest()");
     
        // do real work here or whatever        

     log.info("End handleRequest()");
    }

    

[mobazr]

Hi Ronald,

so the basic difference is: You didn't inject the Helper Class but received it via Components.getInstance().

I tried that and it works. Actually a mistake I could've found out myself, right?! The injection didn't work because of the @BypassInterceptors and therefore the only way to get a component is via the Components.getInstance() method.

Cool. Thanks a million.

Manuel