JEE6 Long Polling WebServlet - Exception after calling AsyncContext#complete

问题

I am trying to implement long polling, however after calling AsyncContext.complete() I get an exception from Weld:

Warnung:   Error invoking requestDestroyed method on ServletRequestListener org.jboss.weld.servlet.WeldListener
java.lang.NullPointerException
    at org.jboss.weld.context.AbstractBoundContext.deactivate(AbstractBoundContext.java:71)
    at org.jboss.weld.context.http.HttpRequestContextImpl.deactivate(HttpRequestContextImpl.java:70)
    at org.jboss.weld.servlet.WeldListener.requestDestroyed(WeldListener.java:154)
    at org.apache.catalina.core.StandardContext.fireRequestDestroyedEvent(StandardContext.java:5261)
    at org.apache.catalina.core.StandardHostValve.postInvoke(StandardHostValve.java:255)
    at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:359)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:260)
    at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:188)
    at org.glassfish.grizzly.http.server.HttpHandler.runService(HttpHandler.java:191)
    at org.glassfish.grizzly.http.server.HttpHandler.doHandle(HttpHandler.java:168)
    at org.glassfish.grizzly.http.server.HttpServerFilter.handleRead(HttpServerFilter.java:189)
    at org.glassfish.grizzly.filterchain.ExecutorResolver$9.execute(ExecutorResolver.java:119)
    at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeFilter(DefaultFilterChain.java:288)
    at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeChainPart(DefaultFilterChain.java:206)
    at org.glassfish.grizzly.filterchain.DefaultFilterChain.execute(DefaultFilterChain.java:136)
    at org.glassfish.grizzly.filterchain.DefaultFilterChain.process(DefaultFilterChain.java:114)
    at org.glassfish.grizzly.ProcessorExecutor.execute(ProcessorExecutor.java:77)
    at org.glassfish.grizzly.nio.transport.TCPNIOTransport.fireIOEvent(TCPNIOTransport.java:838)
    at org.glassfish.grizzly.strategies.AbstractIOStrategy.fireIOEvent(AbstractIOStrategy.java:113)
    at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.run0(WorkerThreadIOStrategy.java:115)
    at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.access$100(WorkerThreadIOStrategy.java:55)
    at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy$WorkerThreadRunnable.run(WorkerThreadIOStrategy.java:135)
    at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:564)
    at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.run(AbstractThreadPool.java:544)
    at java.lang.Thread.run(Thread.java:744)

My Servlet looks as follows:

@WebServlet(urlPatterns = {"/newmsg"}, asyncSupported = true)
public class NewMessageNotifierLongPolling extends HttpServlet {

    private static final Queue<AsyncContext> peers = new ConcurrentLinkedQueue();

    public void notifyClientsAboutNewMessage(@Observes Message msg) {
        for (final AsyncContext ac : peers) {
            try {
                final ServletOutputStream os = ac.getResponse().getOutputStream();
                os.println(msg.getSubject());
                ac.complete();
            } catch (IOException ex) {
                Logger.getLogger(NewMessageNotifierLongPolling.class.getName()).log(Level.SEVERE, null, ex);
            } finally {
                peers.remove(ac);
            }
        }
    }

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType(MediaType.TEXT_PLAIN);
        response.setStatus(202);
        response.setHeader("Pragma", "no-cache");
        response.setCharacterEncoding("UTF-8");
        response.flushBuffer();

        final AsyncContext ac = request.startAsync(request, response);
        ac.setTimeout(35 * 1000);
        ac.addListener(new AsyncListener() {
            @Override
            public void onComplete(AsyncEvent event) throws IOException {
                peers.remove(ac);
            }

            @Override
            public void onTimeout(AsyncEvent event) throws IOException {
                peers.remove(ac);
            }

            @Override
            public void onError(AsyncEvent event) throws IOException {
                peers.remove(ac);
            }

            @Override
            public void onStartAsync(AsyncEvent event) throws IOException {
            }
        });
        peers.add(ac);
    }
}

回答1:

According to this JIRA, there's a bug in Weld 1.1.10 ( present in Tomcat 7.0.23 and related JBoss servers) that causes the Async servlet to lose context between requests to the same servlet.

Upgrading either your Weld or JBoss versions resolves the issue

来源：https://stackoverflow.com/questions/24258951/jee6-long-polling-webservlet-exception-after-calling-asynccontextcomplete