java - 如何将 DeferredResult 与 ListenableFuture 列表结合使用？

Question

我有一个 Guava ListenableFuture 实例和 Spring DeferredResult 的列表。我想为列表中第一个成功的 future 设置结果，或者如果超时尚未到期以从所有 future 中获得成功的结果。这是我的尝试:

DeferredResult<String> foo() {
    DeferredResult<String> result = new DeferredResult<>(3000L);

    List<String> resps = newArrayList();
    List<ListenableFuture<String>> fList = ...

    fList.forEach(f -> Futures.addCallback(f, new FutureCallback<String>() {
        @Override
        public void onSuccess(String resp) {
            resps.add(resp);
        }

        @Override
        public void onFailure(Throwable t) {
            // NOP
        }
    }));

    ListenableFuture<List<String>> f0 = Futures.successfulAsList(fList);

    Futures.addCallback(f0, new FutureCallback<List<String>>() {
        @Override
        public void onSuccess(List<String> r) {
            if (!result.hasResult()) {
                result.
                    if (r != null) {
                        result.setResult(...);
                    }
                }
            }

            @Override
            public void onFailure(Throwable t) {
                // NOP
            }
        }); 

    return result;  
}

我的代码不起作用，因为它等待所有 future 的结果，但我需要关于 DeferredResult 超时的最快结果。我该如何解决？

Answer 1

DeferredResult<String> foo() {
  DeferredResult<String> result = new DeferredResult<>(3000L);

  List<ListenableFuture<String>> fList = ...

  ExecutorService serializingExecutor = Executors.newSingleThreadExecutor();
  fList.forEach(
      f ->
          Futures.addCallback(
              f,
              new FutureCallback<String>() {
                @Override
                public void onSuccess(String value) {
                  if (!result.hasResult()) {
                    result.setResult(value);
                  }
                }

                @Override
                public void onFailure(Throwable throwable) {}
              },
              // To avoid race in the callback:
              serializingExecutor));

  return result;
}