spring mvc @RequestBody @ResponseBody 解析流程

一、此接口测试用例

    @RequestMapping(value = "/save_user",produces = "application/xml;charset=utf-8")@ResponseBodypublic Map<String,Object> saveUser(@RequestBody UserParam userParam) throws Exception{log.info(" get user userParam:" + JSONUtil.toJsonStr(userParam));Map<String,Object> user = new HashMap<String,Object>();user.put("id",userParam.getAge() );user.put("name",userParam.getName() );return  user;
//        return "liming";}

dispatchServlet.xml配置

    <mvc:annotation-driven><mvc:message-converters><bean class="com.tpw.component.AkResponseConverter"></bean><bean class="org.springframework.http.converter.StringHttpMessageConverter"/><bean class="org.springframework.http.converter.json.MappingJackson2HttpMessageConverter"/><bean class="org.springframework.http.converter.xml.MappingJackson2XmlHttpMessageConverter"></bean></mvc:message-converters><mvc:argument-resolvers><bean class="com.tpw.component.RequestPropertiesArgumentResolver"></bean></mvc:argument-resolvers></mvc:annotation-driven>

一、初始化加载解析器和转换器

请求参数由HandlerMethodArgumentResolver解析，返回参数由HandlerMethodReturnValueHandler来解析。这些解析器和返回值转换器存储在RequestMappingHandlerAdapter类中。

1.系统初始化request的参数解析器，这个存储在

RequestMappingHandlerAdapter类的
private HandlerMethodArgumentResolverComposite argumentResolvers;

2 初始化在RequestMappingHandlerAdapter.afterPropertiesSet方法中

public void afterPropertiesSet() {// Do this first, it may add ResponseBody advice beansinitControllerAdviceCache();if (this.argumentResolvers == null) {List<HandlerMethodArgumentResolver> resolvers = getDefaultArgumentResolvers();this.argumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers);}if (this.initBinderArgumentResolvers == null) {List<HandlerMethodArgumentResolver> resolvers = getDefaultInitBinderArgumentResolvers();this.initBinderArgumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers);}if (this.returnValueHandlers == null) {List<HandlerMethodReturnValueHandler> handlers = getDefaultReturnValueHandlers();this.returnValueHandlers = new HandlerMethodReturnValueHandlerComposite().addHandlers(handlers);}}

3 然后会加载26个系统默认的参数解析器

 private List<HandlerMethodArgumentResolver> getDefaultArgumentResolvers() {List<HandlerMethodArgumentResolver> resolvers = new ArrayList<>(30);// Annotation-based argument resolutionresolvers.add(new RequestParamMethodArgumentResolver(getBeanFactory(), false));resolvers.add(new RequestParamMapMethodArgumentResolver());resolvers.add(new PathVariableMethodArgumentResolver());resolvers.add(new PathVariableMapMethodArgumentResolver());resolvers.add(new MatrixVariableMethodArgumentResolver());resolvers.add(new MatrixVariableMapMethodArgumentResolver());resolvers.add(new ServletModelAttributeMethodProcessor(false));resolvers.add(new RequestResponseBodyMethodProcessor(getMessageConverters(), this.requestResponseBodyAdvice));resolvers.add(new RequestPartMethodArgumentResolver(getMessageConverters(), this.requestResponseBodyAdvice));resolvers.add(new RequestHeaderMethodArgumentResolver(getBeanFactory()));resolvers.add(new RequestHeaderMapMethodArgumentResolver());resolvers.add(new ServletCookieValueMethodArgumentResolver(getBeanFactory()));resolvers.add(new ExpressionValueMethodArgumentResolver(getBeanFactory()));resolvers.add(new SessionAttributeMethodArgumentResolver());resolvers.add(new RequestAttributeMethodArgumentResolver());// Type-based argument resolutionresolvers.add(new ServletRequestMethodArgumentResolver());resolvers.add(new ServletResponseMethodArgumentResolver());resolvers.add(new HttpEntityMethodProcessor(getMessageConverters(), this.requestResponseBodyAdvice));resolvers.add(new RedirectAttributesMethodArgumentResolver());resolvers.add(new ModelMethodProcessor());resolvers.add(new MapMethodProcessor());resolvers.add(new ErrorsMethodArgumentResolver());resolvers.add(new SessionStatusMethodArgumentResolver());resolvers.add(new UriComponentsBuilderMethodArgumentResolver());// Custom argumentsif (getCustomArgumentResolvers() != null) {resolvers.addAll(getCustomArgumentResolvers());}// Catch-allresolvers.add(new RequestParamMethodArgumentResolver(getBeanFactory(), true));resolvers.add(new ServletModelAttributeMethodProcessor(true));return resolvers;}

4 这里还会加载自定义参数解析器.自定义参数解析器在dispatch-servlet.xml配置

<mvc:annotation-driven><mvc:message-converters><bean class="org.springframework.http.converter.StringHttpMessageConverter"/><bean class="org.springframework.http.converter.json.MappingJackson2HttpMessageConverter"/></mvc:message-converters><mvc:argument-resolvers><bean class="com.tpw.component.RequestPropertiesArgumentResolver"></bean></mvc:argument-resolvers>
</mvc:annotation-driven>

即可。

5.默认的返回值转换器为

6.@RequestBody和@ResponseBody都由RequestResponseBodyMethodProcessor这个类负责转换。

 @Overridepublic boolean supportsParameter(MethodParameter parameter) {return parameter.hasParameterAnnotation(RequestBody.class);}@Overridepublic boolean supportsReturnType(MethodParameter returnType) {return (AnnotatedElementUtils.hasAnnotation(returnType.getContainingClass(), ResponseBody.class) ||returnType.hasMethodAnnotation(ResponseBody.class));}

7 如果是springboot项目，则写一个CONFIGUATION类实现WebMvcConfigurer接口即可。

org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration的内部类会自动创建RequestMappingHandlerAdapter

@Configuration(proxyBeanMethods = false)
public static class EnableWebMvcConfiguration extends DelegatingWebMvcConfiguration implements ResourceLoaderAware {

@Configuration(proxyBeanMethods = false)public static class EnableWebMvcConfiguration extends DelegatingWebMvcConfiguration implements ResourceLoaderAware {@Bean@Overridepublic RequestMappingHandlerAdapter requestMappingHandlerAdapter(@Qualifier("mvcContentNegotiationManager") ContentNegotiationManager contentNegotiationManager,@Qualifier("mvcConversionService") FormattingConversionService conversionService,@Qualifier("mvcValidator") Validator validator) {RequestMappingHandlerAdapter adapter = super.requestMappingHandlerAdapter(contentNegotiationManager,conversionService, validator);adapter.setIgnoreDefaultModelOnRedirect(this.mvcProperties == null || this.mvcProperties.isIgnoreDefaultModelOnRedirect());return adapter;}

然后会调用WebMvcConfigurationSupport.requestMappingHandlerAdapter

public RequestMappingHandlerAdapter requestMappingHandlerAdapter(@Qualifier("mvcContentNegotiationManager") ContentNegotiationManager contentNegotiationManager,@Qualifier("mvcConversionService") FormattingConversionService conversionService,@Qualifier("mvcValidator") Validator validator) {RequestMappingHandlerAdapter adapter = createRequestMappingHandlerAdapter();adapter.setContentNegotiationManager(contentNegotiationManager);adapter.setMessageConverters(getMessageConverters());adapter.setWebBindingInitializer(getConfigurableWebBindingInitializer(conversionService, validator));adapter.setCustomArgumentResolvers(getArgumentResolvers());adapter.setCustomReturnValueHandlers(getReturnValueHandlers());if (jackson2Present) {adapter.setRequestBodyAdvice(Collections.singletonList(new JsonViewRequestBodyAdvice()));adapter.setResponseBodyAdvice(Collections.singletonList(new JsonViewResponseBodyAdvice()));}AsyncSupportConfigurer configurer = new AsyncSupportConfigurer();configureAsyncSupport(configurer);if (configurer.getTaskExecutor() != null) {adapter.setTaskExecutor(configurer.getTaskExecutor());}if (configurer.getTimeout() != null) {adapter.setAsyncRequestTimeout(configurer.getTimeout());}adapter.setCallableInterceptors(configurer.getCallableInterceptors());adapter.setDeferredResultInterceptors(configurer.getDeferredResultInterceptors());return adapter;}

最终会调用WebMvcConfigurerComposite.addArgumentResolvers，这个类的List<WebMvcConfigurer> delegates 即为当前容器所有实现了WebMvcConfigurer接口的类。

WebMvcConfigurerComposite@Overridepublic void addArgumentResolvers(List<HandlerMethodArgumentResolver> argumentResolvers) {for (WebMvcConfigurer delegate : this.delegates) {delegate.addArgumentResolvers(argumentResolvers);}}

二、@RequestBody请求解析流程

1.DispatcherServlet.doDispatch 中间会调用当前请求接口方法中所有支持的参数解析器，进行相应的参数解析和转换。

InvocableHandlerMethod.getMethodArgumentValues

protected Object[] getMethodArgumentValues(NativeWebRequest request, @Nullable ModelAndViewContainer mavContainer,Object... providedArgs) throws Exception {MethodParameter[] parameters = getMethodParameters();if (ObjectUtils.isEmpty(parameters)) {return EMPTY_ARGS;}Object[] args = new Object[parameters.length];for (int i = 0; i < parameters.length; i++) {MethodParameter parameter = parameters[i];parameter.initParameterNameDiscovery(this.parameterNameDiscoverer);args[i] = findProvidedArgument(parameter, providedArgs);if (args[i] != null) {continue;}if (!this.resolvers.supportsParameter(parameter)) {throw new IllegalStateException(formatArgumentError(parameter, "No suitable resolver"));}try {args[i] = this.resolvers.resolveArgument(parameter, mavContainer, request, this.dataBinderFactory);}}return args;}

这里面的this.resolvers的参数赋值来源于RequestMappingHandlerAdapter.invokeHandlerMethod，这个方法创建InvocableHandlerMethod，并设置解析器参数

@Nullableprotected ModelAndView invokeHandlerMethod(HttpServletRequest request,HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {ServletWebRequest webRequest = new ServletWebRequest(request, response);try {WebDataBinderFactory binderFactory = getDataBinderFactory(handlerMethod);ModelFactory modelFactory = getModelFactory(handlerMethod, binderFactory);ServletInvocableHandlerMethod invocableMethod = createInvocableHandlerMethod(handlerMethod);if (this.argumentResolvers != null) {invocableMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers);}if (this.returnValueHandlers != null) {invocableMethod.setHandlerMethodReturnValueHandlers(this.returnValueHandlers);}invocableMethod.setDataBinderFactory(binderFactory);invocableMethod.setParameterNameDiscoverer(this.parameterNameDiscoverer);ModelAndViewContainer mavContainer = new ModelAndViewContainer();mavContainer.addAllAttributes(RequestContextUtils.getInputFlashMap(request));modelFactory.initModel(webRequest, mavContainer, invocableMethod);mavContainer.setIgnoreDefaultModelOnRedirect(this.ignoreDefaultModelOnRedirect);AsyncWebRequest asyncWebRequest = WebAsyncUtils.createAsyncWebRequest(request, response);asyncWebRequest.setTimeout(this.asyncRequestTimeout);WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);asyncManager.setTaskExecutor(this.taskExecutor);asyncManager.setAsyncWebRequest(asyncWebRequest);asyncManager.registerCallableInterceptors(this.callableInterceptors);asyncManager.registerDeferredResultInterceptors(this.deferredResultInterceptors);invocableMethod.invokeAndHandle(webRequest, mavContainer);if (asyncManager.isConcurrentHandlingStarted()) {return null;}return getModelAndView(mavContainer, modelFactory, webRequest);}finally {webRequest.requestCompleted();}}

2.然后会调用RequestResponseBodyMethodProcessor.resolveArgument接口进行参数解析。

public Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception {parameter = parameter.nestedIfOptional();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);}

3.readWithMessageConverters(webRequest, parameter, parameter.getNestedGenericParameterType()) 最终会调用

AbstractMessageConverterMethodArgumentResolver.readWithMessageConverters进行参数解析。

此函数内会使用当前容器中所有的messageConvert类BEAN测试是否支持可读，如果可读的话，则进行messageConvert的读转换接口。

protected <T> Object readWithMessageConverters(HttpInputMessage inputMessage, MethodParameter parameter,Type targetType) throws IOException, HttpMediaTypeNotSupportedException, HttpMessageNotReadableException {MediaType contentType;boolean noContentType = false;Object body = NO_VALUE;EmptyBodyCheckingHttpInputMessage message;try {message = new EmptyBodyCheckingHttpInputMessage(inputMessage);for (HttpMessageConverter<?> converter : this.messageConverters) {Class<HttpMessageConverter<?>> converterType = (Class<HttpMessageConverter<?>>) converter.getClass();GenericHttpMessageConverter<?> genericConverter =(converter instanceof GenericHttpMessageConverter ? (GenericHttpMessageConverter<?>) converter : null);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);body = (genericConverter != null ? genericConverter.read(targetType, contextClass, msgToUse) :((HttpMessageConverter<T>) converter).read(targetClass, msgToUse));body = getAdvice().afterBodyRead(body, msgToUse, parameter, targetType, converterType);}else {body = getAdvice().handleEmptyBody(null, message, parameter, targetType, converterType);}break;}}}return body;}

这里的messageConvert实际上是MappingJackson2HttpMessageConverter，他支持JSON转换

public MappingJackson2HttpMessageConverter(ObjectMapper objectMapper) {super(objectMapper, MediaType.APPLICATION_JSON, new MediaType("application", "*+json"));
}

4.resolveArgument方法中的validateIfApplicable(binder, parameter)会对带有@validate注解的参数进行校验。

5.解析完生成参数实体对象。

三、@Responsebody解析流程

1.接口方法执行完后，会调用HandlerMethodReturnValueHandlerComposite.

handleReturnValue进行转换。这里寻找系统中所有returnHandler,查找是否支持可写的HANDLER，进行处理。

 public void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType,ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {HandlerMethodReturnValueHandler handler = selectHandler(returnValue, returnType);if (handler == null) {throw new IllegalArgumentException("Unknown return value type: " + returnType.getParameterType().getName());}handler.handleReturnValue(returnValue, returnType, mavContainer, webRequest);}

找HANDLER的原则是看是否支持。

 RequestResponseBodyMethodProcessor
public boolean supportsReturnType(MethodParameter returnType) {return (AnnotatedElementUtils.hasAnnotation(returnType.getContainingClass(), ResponseBody.class) ||returnType.hasMethodAnnotation(ResponseBody.class));}

2.最终会调用到AbstractMessageConverterMethodProcessor.writeWithMessageConverters进行结果转换，这里又会寻找当前系统中所有的messageConvert类，找到支持写的类，进行数据转换。然后返回。

 protected <T> void writeWithMessageConverters(@Nullable T value, MethodParameter returnType,ServletServerHttpRequest inputMessage, ServletServerHttpResponse outputMessage)throws IOException, HttpMediaTypeNotAcceptableException, HttpMessageNotWritableException {Object body;Class<?> valueType;Type targetType;if (selectedMediaType != null) {selectedMediaType = selectedMediaType.removeQualityValue();for (HttpMessageConverter<?> converter : this.messageConverters) {GenericHttpMessageConverter genericConverter = (converter instanceof GenericHttpMessageConverter ?(GenericHttpMessageConverter<?>) converter : null);if (genericConverter != null ?((GenericHttpMessageConverter) converter).canWrite(targetType, valueType, selectedMediaType) :converter.canWrite(valueType, selectedMediaType)) {body = getAdvice().beforeBodyWrite(body, returnType, selectedMediaType,(Class<? extends HttpMessageConverter<?>>) converter.getClass(),inputMessage, outputMessage);if (body != null) {Object theBody = body;LogFormatUtils.traceDebug(logger, traceOn ->"Writing [" + LogFormatUtils.formatValue(theBody, !traceOn) + "]");addContentDispositionHeader(inputMessage, outputMessage);if (genericConverter != null) {genericConverter.write(body, targetType, selectedMediaType, outputMessage);}else {((HttpMessageConverter) converter).write(body, selectedMediaType, outputMessage);}}else {if (logger.isDebugEnabled()) {logger.debug("Nothing to write: null body");}}return;}}}}

这里找到的是MappingJackson2XmlHttpMessageConverter

最终通过objMapper进行对象转换。我这里配置的返回类型为XML.

最终将XML的数据流写入resonse.

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