异步web服务，回调问题

Question

我有一个使用axis2的异步web服务，我使用相同的CallBack汉化器调用了它两次，如下所示：

stub.startGetData("Foo",callbackhandler)
 stub.startGetData("bar",callbackhanlder)

 ServiceCallBackhandler callbackhandler =  new ServiceCallBackhandler() { .....};
 //ServiceCallBackhanlder and stub are generated from a WSDL file

 Synchronized(callbackhandler){ callbackhandler.wait()}
 //remaining code to be executed
      ............
      ...........

这种情况下的问题是，一旦调用在stub.startGetData("Foo",callbackhandler)之后返回，就会执行“剩余代码”。我希望回调一直等到处理完stub.startGetData("boo",callbackhandler)语句，然后执行剩下的代码。有没有办法不使用两个不同的回调处理程序，因为两个返回值的处理是相同的。谢谢。

Answer 1

我想你想要这样的东西...

 import java.util.concurrent.CountDownLatch;
 ...

 // set the latch count to the nuber of callbacks to wait for
 CountDownLatch latch = new CountDownLatch(2);

 ServiceCallBackhandler callbackhandler =  new ServiceCallBackhandler() {
      public void handleResponse(Response response) {
           .... do real work ...
           latch.countDown();
      }
 };

 stub.startGetData("Foo",callbackhandler)
 stub.startGetData("bar",callbackhanlder)

 // wait for both callbacks to occur
 latch.await();

另请参阅java.util.concurrent.Semaphore，但我认为CountDownLatch正是您所需要的。

Answer 2

一般来说，如果一个人想要等待N个不同对象的特定条件成立，他们应该考虑使用并发实用程序中的CyclicBarrier(N)或CountDownLatch(N)。

调用体的基本结构：

CountDownLatch my_latch = new CountDownLatch( 2 );

// These objects perform some asynchronous function when
// their start() method is called.
AsyncObject ao1 = new AsyncObject( my_latch, ... );
AsyncObject ao2 = new AsyncObject( my_latch, ... );

ao1.start();  // asynchronous, returns immediately
ao2.start();  // asynchronous, returns immediately

// my_latch.await() blocks until the latch has counted down to 0 from 2
my_latch.await();

并从希望在其工作完成或满足条件时“发信号”的方法中：

{
    // ... work ...
    // work is complete

    the_latch_passed_in_to_this_object.countDown();
 }