目录
前言
springmvc支持异步的方式返回数据，处理异步任务的HandlerMethodReturnValueHandler有AsyncTaskMethodReturnValueHandler、CallableMethodReturnValueHandler、StreamingResponseBodyReturnValueHandler、DeferredResultMethodReturnValueHandler。
一、AsyncTaskMethodReturnValueHandler
用于处理返回值是WebAsyncTask类型
@Override
public boolean supportsReturnType(MethodParameter returnType) {
//返回值是WebAsyncTask类型
return WebAsyncTask.class.isAssignableFrom(returnType.getParameterType());
}
@Override
public void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType,
ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {
if (returnValue == null) {
mavContainer.setRequestHandled(true);
return;
}
WebAsyncTask<?> webAsyncTask = (WebAsyncTask<?>) returnValue;
if (this.beanFactory != null) {
webAsyncTask.setBeanFactory(this.beanFactory);
}
//调用异步管理器执行任务
WebAsyncUtils.getAsyncManager(webRequest).startCallableProcessing(webAsyncTask, mavContainer);
}
二、CallableMethodReturnValueHandler
用于处理Callable类型
@Override
public boolean supportsReturnType(MethodParameter returnType) {
//返回值是Callable类型
return Callable.class.isAssignableFrom(returnType.getParameterType());
}
@Override
public void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType,
ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {
if (returnValue == null) {
mavContainer.setRequestHandled(true);
return;
}
Callable<?> callable = (Callable<?>) returnValue;
//调用异步管理器执行任务
WebAsyncUtils.getAsyncManager(webRequest).startCallableProcessing(callable, mavContainer);
}
三、StreamingResponseBodyReturnValueHandler
用于处理返回值是StreamingResponseBody类型或者ResponseEntity类型并且body是StreamingResponseBody类型
@Override
public boolean supportsReturnType(MethodParameter returnType) {
//StreamingResponseBody类型
if (StreamingResponseBody.class.isAssignableFrom(returnType.getParameterType())) {
return true;
}
//ResponseEntity类型，body是StreamingResponseBody类型
else if (ResponseEntity.class.isAssignableFrom(returnType.getParameterType())) {
Class<?> bodyType = ResolvableType.forMethodParameter(returnType).getGeneric().resolve();
return (bodyType != null && StreamingResponseBody.class.isAssignableFrom(bodyType));
}
return false;
}
@Override
@SuppressWarnings("resource")
public void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType,
ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {
if (returnValue == null) {
mavContainer.setRequestHandled(true);
return;
}
HttpServletResponse response = webRequest.getNativeResponse(HttpServletResponse.class);
Assert.state(response != null, "No HttpServletResponse");
ServerHttpResponse outputMessage = new ServletServerHttpResponse(response);
if (returnValue instanceof ResponseEntity) {
ResponseEntity<?> responseEntity = (ResponseEntity<?>) returnValue;
//状态码
response.setStatus(responseEntity.getStatusCodeValue());
//响应头
outputMessage.getHeaders().putAll(responseEntity.getHeaders());
//响应数据
returnValue = responseEntity.getBody();
if (returnValue == null) {
mavContainer.setRequestHandled(true);
outputMessage.flush();
return;
}
}
ServletRequest request = webRequest.getNativeRequest(ServletRequest.class);
Assert.state(request != null, "No ServletRequest");
ShallowEtagHeaderFilter.disableContentCaching(request);
Assert.isInstanceOf(StreamingResponseBody.class, returnValue, "StreamingResponseBody expected");
StreamingResponseBody streamingBody = (StreamingResponseBody) returnValue;
//创建StreamingResponseBodyTask
Callable<Void> callable = new StreamingResponseBodyTask(outputMessage.getBody(), streamingBody);
//调用异步管理器执行任务
WebAsyncUtils.getAsyncManager(webRequest).startCallableProcessing(callable, mavContainer);
}
四、DeferredResultMethodReturnValueHandler
用于处理DeferredResult、ListenableFuture、CompletionStage类型
@Override
public boolean supportsReturnType(MethodParameter returnType) {
Class<?> type = returnType.getParameterType();
//类型校验
return (DeferredResult.class.isAssignableFrom(type) ||
ListenableFuture.class.isAssignableFrom(type) ||
CompletionStage.class.isAssignableFrom(type));
}
@Override
public void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType,
ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {
if (returnValue == null) {
mavContainer.setRequestHandled(true);
return;
}
DeferredResult<?> result;
//DeferredResult类型
if (returnValue instanceof DeferredResult) {
result = (DeferredResult<?>) returnValue;
}
//ListenableFuture类型，适配成DeferredResult类型
else if (returnValue instanceof ListenableFuture) {
result = adaptListenableFuture((ListenableFuture<?>) returnValue);
}
CompletionStage类型，适配成DeferredResult类型
else if (returnValue instanceof CompletionStage) {
result = adaptCompletionStage((CompletionStage<?>) returnValue);
}
else {
// Should not happen...
throw new IllegalStateException("Unexpected return value type: " + returnValue);
}
//调用异步管理器执行任务
WebAsyncUtils.getAsyncManager(webRequest).startDeferredResultProcessing(result, mavContainer);
}