给前端返回一个json数据SpringMVC到底支持哪些返回值关于源码
给前端返回一个json数据@Controller
public class ResponseTestController {
@ResponseBody //利用返回值处理器里面的消息转换器进行处理
@GetMapping(value = "/test/person")
public Person getPerson(){
Person person = new Person();
person.setAge(28);
person.setBirth(new Date());
person.setUserName("zhangsan");
return person;
}
}
SpringMVC到底支持哪些返回值
ModelAndView
Model
View
ResponseEntity
ResponseBodyEmitter
StreamingResponseBody
HttpEntity
HttpHeaders
Callable
DeferredResult
ListenableFuture
CompletionStage
WebAsyncTask
有 @ModelAttribute 且为对象类型的
@ResponseBody 注解 —> RequestResponseBodyMethodProcessor；
public class RequestMappingHandlerAdapter extends AbstractHandlerMethodAdapter
implements BeanFactoryAware, InitializingBean {
...
@Nullable
protected ModelAndView invokeHandlerMethod(HttpServletRequest request,
HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
ServletWebRequest webRequest = new ServletWebRequest(request, response);
try {
...
ServletInvocableHandlerMethod invocableMethod = createInvocableHandlerMethod(handlerMethod);
if (this.argumentResolvers != null) {
invocableMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers);
}
if (this.returnValueHandlers != null) {//<----关注点
invocableMethod.setHandlerMethodReturnValueHandlers(this.returnValueHandlers);
}
...
invocableMethod.invokeAndHandle(webRequest, mavContainer);//看下块代码
if (asyncManager.isConcurrentHandlingStarted()) {
return null;
}
return getModelAndView(mavContainer, modelFactory, webRequest);
}
finally {
webRequest.requestCompleted();
}
}
public class ServletInvocableHandlerMethod extends InvocableHandlerMethod {
public void invokeAndHandle(ServletWebRequest webRequest, ModelAndViewContainer mavContainer,
Object... providedArgs) throws Exception {
Object returnValue = invokeForRequest(webRequest, mavContainer, providedArgs);
...
try {
//看下块代码
this.returnValueHandlers.handleReturnValue(
returnValue, getReturnValueType(returnValue), mavContainer, webRequest);
}
catch (Exception ex) {
...
}
}
public class HandlerMethodReturnValueHandlerComposite implements HandlerMethodReturnValueHandler {
...
@Override
public void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType,
ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {
//selectHandler()实现在下面
HandlerMethodReturnValueHandler handler = selectHandler(returnValue, returnType);
if (handler == null) {
throw new IllegalArgumentException("Unknown return value type: " + returnType.getParameterType().getName());
}
//开始处理
handler.handleReturnValue(returnValue, returnType, mavContainer, webRequest);
}
@Nullable
private HandlerMethodReturnValueHandler selectHandler(@Nullable Object value, MethodParameter returnType) {
boolean isAsyncValue = isAsyncReturnValue(value, returnType);
for (HandlerMethodReturnValueHandler handler : this.returnValueHandlers) {
if (isAsyncValue && !(handler instanceof AsyncHandlerMethodReturnValueHandler)) {
continue;
}
if (handler.supportsReturnType(returnType)) {
return handler;
}
}
return null;
}
@ResponseBody 注解，即RequestResponseBodyMethodProcessor，它实现HandlerMethodReturnValueHandler接口
public class RequestResponseBodyMethodProcessor extends AbstractMessageConverterMethodProcessor {
...
@Override
public void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType,
ModelAndViewContainer mavContainer, NativeWebRequest webRequest)
throws IOException, HttpMediaTypeNotAcceptableException, HttpMessageNotWritableException {
mavContainer.setRequestHandled(true);
ServletServerHttpRequest inputMessage = createInputMessage(webRequest);
ServletServerHttpResponse outputMessage = createOutputMessage(webRequest);
// 使用消息转换器进行写出操作，本方法下一章节介绍：
// Try even with null return value. ResponseBodyAdvice could get involved.
writeWithMessageConverters(returnValue, returnType, inputMessage, outputMessage);
}
}
