java如何在单独的线程中执行大量WS调用并增加单个结果变量？

Question

线程初学者在这里

在Struts操作中，我需要通过多次调用Web服务来检索一些数据，每次调用不同的请求，并等待每个请求完成，以便显示结果

所以基本上我是这样做的：

// The list of the region codes used for the requests
List<String> codesRegions;

// Init of a variable containing the total amount of data
Integer totalAmount = 0; 

// For every region
for(String codeRegion : codesRegions)
{
    MyRegionStub stub = createRegionStub();

    // Call of the WS with the code region
    MyRegionRequest request = new MyRegionRequest();
    request.setCodeRegion(codeRegion);

    // Getting the number associated to the region and incrementing totalAmount
    MyRegionResponse response = stub.getRegionStats(request);
    totalAmount += response.getRegionStats();
}

// Once all the calls are done, I display the result
request.setAttribute("totalAmount", totalAmount);
mapping.findForward("success");

我的问题是，由于我多次调用此WS，因此经常会出现超时错误。所以我想知道如何在一个单独的线程中执行每个调用，并毫无错误地递增相同的结果变量

我想知道的另一件事是，我需要等待所有调用完成后才能显示数据。我需要做什么才能在完成后调用mapping.findForward("success");

Answer 1

您可以将Executor framework与CountDownLatch一起使用。 ExecutorService将在线程池中执行异步任务，CountDownLatch将等待所有任务完成

在这种情况下，您应该注意countDownLatch.countDown();必须出现在finally块中，这样它就可以保证被执行，并且对于总数量，您应该使用线程安全的AtomicInteger

您的代码如下所示：

ExecutorService threadPool = Executors.newFixedThreadPool(10);
CountDownLatch countDownLatch = new CountDownLatch(codesRegions.size());
AtomicInteger totalAmount = new AtomicInteger(0);

for (String codeRegion : codesRegions)
{
    threadPool.execute(new Runnable() {

        @Override
        public void run()
        {
            try
            {
                MyRegionStub stub = createRegionStub();

                // Call of the WS with the code region
                MyRegionRequest request = new MyRegionRequest();
                request.setCodeRegion(codeRegion);

                // Getting the number associated to the region and
                // incrementing
                // totalAmount
                MyRegionResponse response = stub.getRegionStats(request);
                totalAmount.addAndGet(response.getRegionStats());
            }
            finally
            {
                countDownLatch.countDown();
            }
        }
    });
}
try
{
    countDownLatch.await();
}
catch (InterruptedException e)
{
    //Return ERROR in case of current thread is interrupted.
}
// Once all the calls are done, I display the result
request.setAttribute("totalAmount", totalAmount);
mapping.findForward("success");

Answer 2

如果您使用的是java 8，我建议CompletableFuture

这将允许您创建一个运行异步的线程负载，比如

 CompleteableFuture<Integer> future CompleteableFuture.supplyAsync(getRegionStats(codeRegion))

一旦你创建了所有的未来，你就可以检查它们何时全部完成

 CompleteableFuture.allOf(future1, future2).join();

然后，对于你的每一个未来，你可以做价值总和

 for(CompleteableFuture future : futures)
      totalAmount+= future.get()