JAX-RS and Long Polling

Question

I'm trying to use long polling with JAX-RS (Jersey implementation) and it doesn't work as I expect. Maybe I'm misunderstanding something. I would appreciate any advice.

Please note that using a reverse connection (something like Atmosphere, Comet, etc) is not a option for security reason. Not that I'm currently developing with Tomcat 7.

The following method is invoked from a JQuery Ajax call (using $.ajax).

@Path("/poll")
@GET
public void poll(@Suspended final AsyncResponse asyncResponse)
        throws InterruptedException {
    new Thread(new Runnable() {
        @Override
        public void run() {
            this.asyncResponse = asyncResponse;
            // wait max. 30 seconds using a CountDownLatch
            latch.await(getTimeout(), TimeUnit.SECONDS);
        }
    }).start();
}

The other method is invoked from my application (after a JMS call):

@POST
@Path("/printed")
public Response printCallback() {
    // ...

    // I expect the /poll call to be ended here from the client perspective but that is not the case
    asyncResponse.resume("UPDATE"); 
    latch.countDown();

    return Response.ok().build();
}

If I remove the Thread creation in the poll method. Then it works, but the problem is that a Thread is busy. If I use the Thread creation, then the method is returning directly and the browser is not detecting the end of the long polling.

What am I doing wrong?

Answer 1

I found the solution of my problem. The problem was in the configuration. We must specify that the Jersey servlet supports async and then it works fine:

<servlet>
    <servlet-name>Jersey REST Service</servlet-name>
    <servlet-class>org.glassfish.jersey.servlet.ServletContainer</servlet-class>
    <async-supported>true</async-supported>
    ...
</servlet>

Please note that if you have Servlet filters, they also need to be async-supported to true.

This was also not necessary to create a thread. Jersey does it for me:

@Path("/poll")
@GET
public void poll(@Suspended final AsyncResponse asyncResponse)
        throws InterruptedException {
    asyncResponse.setTimeout(30, TimeUnit.SECONDS);
    this.asyncResponse = asyncResponse;
}

@POST
@Path("/printed")
public Response printCallback(String barcode) throws IOException {
    // ...

    this.asyncResponse.resume("MESSAGE");

    return Response.ok().build();
}

When calling poll the browser waits until receiving MESSAGE or receiving a HTTP status 503 if the timeout is elapsed. In the server, the request thread is not blocked until the timeout but released directly. In the client side, I have a JavaScript which is calling the method again if the timeout occurs, otherwise I process something in the page.