spring4-3 适配jdk8的CompletableFuture

旧版本（<4.3）

@Override
	public void handleReturnValue(Object returnValue, MethodParameter returnType,
			ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {

		if (returnValue == null) {
			mavContainer.setRequestHandled(true);
			return;
		}

		DeferredResult deferredResult = (DeferredResult) returnValue;
		WebAsyncUtils.getAsyncManager(webRequest).startDeferredResultProcessing(deferredResult, mavContainer);
	}

新版本（≥4.3）

@Override
	public void handleReturnValue(Object returnValue, MethodParameter returnType,
			ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {

		if (returnValue == null) {
			mavContainer.setRequestHandled(true);
			return;
		}

		DeferredResultAdapter adapter = getAdapterFor(returnValue.getClass());
		if (adapter == null) {
			throw new IllegalStateException(
					"Could not find DeferredResultAdapter for return value type: " + returnValue.getClass());
		}
		DeferredResult result = adapter.adaptToDeferredResult(returnValue);
		WebAsyncUtils.getAsyncManager(webRequest).startDeferredResultProcessing(result, mavContainer);
	}

这里面添加了对CompletionStage（CompletableFuture）的特殊处理，即将CompletableFuture适配为DeferredResult

@UsesJava8
	private static class CompletionStageAdapter implements DeferredResultAdapter {

		@Override
		public DeferredResult adaptToDeferredResult(Object returnValue) {
			Assert.isInstanceOf(CompletionStage.class, returnValue, "CompletionStage expected");
			final DeferredResult