@RequestBody注解和@ResponseBody注解实现原理源码剖析+自定义消息转换器

2024-06-01 18:17| 来源: 网络整理| 查看: 265

@RequestBody：将请求中的参数json转换为对象 @ResponseBody：将对象转换为json响应给浏览器 @RequestBody和@ResponseBody的解析都发生在SpringMVC处理请求的第四步HandlerAdapter执行Handler逻辑并返回ModelAndView，此处只贴主要流程代码，全流程代码及处理请求的其他步骤请参考上篇文章：SpringMVC请求流程处理源码剖析

第四部主要做了三件事情：

遍历handler形参，根据不同形参类型以及是否存在@RequestBody、@RequestParam等和注解获取不同的参数解析器，利用参数解析器在请求中获取实参反射调用Handler业务方法，获取返回值根据返回值类型及方法是否存在@ResponseBody获取不同的返回值处理器，利用返回值处理器封装ModelAndView 一、@RequestBody源码分析（完成第四步骤的第一个事情）

首先进入获取handler实参的方法InvocableHandlerMethod#getMethodArgumentValues

protected Object[] getMethodArgumentValues(NativeWebRequest request, @Nullable ModelAndViewContainer mavContainer, Object... providedArgs) throws Exception { // 获取当前handler方法的形参 MethodParameter[] parameters = getMethodParameters(); if (ObjectUtils.isEmpty(parameters)) { return EMPTY_ARGS; } // 创建新数组，用于封装handler被调用时的实参（不同类型的形参获取方式不一样） Object[] args = new Object[parameters.length]; // 遍历形参 for (int i = 0; i continue; } if (!this.resolvers.supportsParameter(parameter)) { throw new IllegalStateException(formatArgumentError(parameter, "No suitable resolver")); } try { // 根据形参获取实参 args[i] = this.resolvers.resolveArgument(parameter, mavContainer, request, this.dataBinderFactory); } catch (Exception ex) { // Leave stack trace for later, exception may actually be resolved and handled... if (logger.isDebugEnabled()) { String exMsg = ex.getMessage(); if (exMsg != null && !exMsg.contains(parameter.getExecutable().toGenericString())) { logger.debug(formatArgumentError(parameter, exMsg)); } } throw ex; } } return args; }

进入resolveArgument方法，获取对应的参数解析器并获取实参

HandlerMethodArgumentResolverComposite.class public Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer, NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception { // 根据不同类型的参数获取不同的参数解析器。如：String的参数解析器AbstractNamedValueMethodArgumentResolver、Map的参数解析器MapMethodProcessor、带有@RequestBody注解的参数解析器RequestResponseBodyMethodProcessor等 HandlerMethodArgumentResolver resolver = getArgumentResolver(parameter); if (resolver == null) { throw new IllegalArgumentException("Unsupported parameter type [" + parameter.getParameterType().getName() + "]. supportsParameter should be called first."); } // 利用对应的参数解析器解析形参获取实参 return resolver.resolveArgument(parameter, mavContainer, webRequest, binderFactory); }

进入getArgumentResolver

HandlerMethodArgumentResolverComposite.class private HandlerMethodArgumentResolver getArgumentResolver(MethodParameter parameter) { HandlerMethodArgumentResolver result = this.argumentResolverCache.get(parameter); if (result == null) { // 遍历参数处理器集合根据参数获取合适的参数处理器（适配器模式）处理@RequestBody的参数处理器是RequestResponseBodyMethodProcessor for (HandlerMethodArgumentResolver resolver : this.argumentResolvers) { if (resolver.supportsParameter(parameter)) { result = resolver; this.argumentResolverCache.put(parameter, result); break; } } } return result; }

进入supportsParameter,判断参数中是否带有@RequestBody注解如果有则此参数用RequestResponseBodyMethodProcessor解析器解析。

RequestResponseBodyMethodProcessor.class public boolean supportsParameter(MethodParameter parameter) { return parameter.hasParameterAnnotation(RequestBody.class); }

拿到参数解析器后进入RequestResponseBodyMethodProcessor#resolveArgument

public Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer, NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception { parameter = parameter.nestedIfOptional(); // 使用消息转换器读取，将请求中的参数读取转换成对象 Object arg = readWithMessageConverters(webRequest, parameter, parameter.getNestedGenericParameterType()); String name = Conventions.getVariableNameForParameter(parameter); if (binderFactory != null) { WebDataBinder binder = binderFactory.createBinder(webRequest, arg, name); if (arg != null) { validateIfApplicable(binder, parameter); if (binder.getBindingResult().hasErrors() && isBindExceptionRequired(binder, parameter)) { throw new MethodArgumentNotValidException(parameter, binder.getBindingResult()); } } if (mavContainer != null) { mavContainer.addAttribute(BindingResult.MODEL_KEY_PREFIX + name, binder.getBindingResult()); } } return adaptArgumentIfNecessary(arg, parameter); }

进入AbstractMessageConverterMethodArgumentResolver#readWithMessageConverters

protected Object readWithMessageConverters(HttpInputMessage inputMessage, MethodParameter parameter, Type targetType) throws IOException, HttpMediaTypeNotSupportedException, HttpMessageNotReadableException { MediaType contentType; boolean noContentType = false; try { // 获取contentType application/json contentType = inputMessage.getHeaders().getContentType(); } catch (InvalidMediaTypeException ex) { throw new HttpMediaTypeNotSupportedException(ex.getMessage()); } if (contentType == null) { noContentType = true; contentType = MediaType.APPLICATION_OCTET_STREAM; } Class contextClass = parameter.getContainingClass(); // 获取参数类型 Class targetClass = (targetType instanceof Class ? (Class) targetType : null); if (targetClass == null) { ResolvableType resolvableType = ResolvableType.forMethodParameter(parameter); targetClass = (Class) resolvableType.resolve(); } HttpMethod httpMethod = (inputMessage instanceof HttpRequest ? ((HttpRequest) inputMessage).getMethod() : null); Object body = NO_VALUE; EmptyBodyCheckingHttpInputMessage message; try { message = new EmptyBodyCheckingHttpInputMessage(inputMessage); // 遍历消息转换器，可以自定义消息转换器只要注入到HandlerAdapter的messageConverters属性 for (HttpMessageConverter converter : this.messageConverters) { Class converterType = (Class) converter.getClass(); GenericHttpMessageConverter genericConverter = (converter instanceof GenericHttpMessageConverter ? (GenericHttpMessageConverter) converter : null); // 过滤合适的消息转换器canRead的底层判断逻辑是（该转换器是否包含请求中Content-Type指定的MediaType和改转换器的supports方法是否为true共同决定是否使用此消息转换器解析参数） if (genericConverter != null ? genericConverter.canRead(targetType, contextClass, contentType) : (targetClass != null && converter.canRead(targetClass, contentType))) { if (message.hasBody()) { HttpInputMessage msgToUse = getAdvice().beforeBodyRead(message, parameter, targetType, converterType); // 使用消息转换器转换消息read(targetClass, msgToUse) targetClass：目标参数类型、msgToUse：包含json的输入流，red的底层方法是readInternal(Class

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