I need a thread in Web/JavaEE container to complete AsyncContext objs in same JVM

问题

I need a thread in Web/JavaEE container to fetch information from an external source and complete corresponding AsyncContext objs in same JVM.

I wish to have a zero-added-latency solution, so periodic polling or a timer is ruled out.

I could start a thread but I believe it is frowned upon in a Web container and not portable. Q1. Is it possible to run a thread portably in a Java EE container instead?

Q2. If I want to run a thread in a Web Container anyway, what is the "least of all evil" ways? InitializeContext? ExecutorService? Thread.run?

Thanks!

回答1:

AsyncContext.html#start is probably the closest you can get.

回答2:

You can use work manager in jsr237 for creating a thread in a Java EE container. : http://jcp.org/en/jsr/detail?id=237. If you want an asynchronous job, you should use JMS.

回答3:

In Java EE 6, you can put the @Asynchronous annotation on an EJB method to have the work in that method be handled by a special thread-pool:

@Stateless
public class SomeBean {

    @Asynchronous
    public void doSomething() {
        // ...
    }
}

Then somewhere else, inject this bean and call the doSomething() method. Control will return immediately.

@WebServlet("/test")
public class SyncServlet extends HttpServlet {

    @EJB
    private SomeBean someBean;

    @Override
    public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        someBean.doSomething();
    }
}

Note that you might not need something like AsyncContext asyncContext = request.startAsync() here. You would use this only if the asynchronous code would still need to send something to the response.

If you need something akin to a period timer though, and not do something in response to a request, you can use the timer service in a singleton:

@Startup
@Singleton
public class SomeTimerBean {

    @Schedule(hour = "*", minute = "*/30", second = "0", persistent = false)
    public void doStuff() {
        // ...
    }
}

Instead of running periodically, you can also run something like this once using the @TimeOut annotation:

@Startup
@Singleton
public class SomeTimerBean {

    @Resource
    private TimerService timerService;

    @Postconstruct
    public void init() {
         timerService.createSingleActionTimer(0, new TimerConfig(null, false));
    }

    @Timeout
    public void doStuff(Timer timer) {
        // ...
    }
}

You can have variants on this, e.g. SomeTimerBean can also call an @Asynchronous method in an other bean as well to basically have the same effect.

来源：https://stackoverflow.com/questions/10276028/i-need-a-thread-in-web-javaee-container-to-complete-asynccontext-objs-in-same-jv