spring-mvc 是如何选择 messageConverter
不要问我阅读spring源码有什么用,问就是没有用,只是让我本身使用spring的过程当中自信点!java
相关文章
spring-相关文章web
相关连接
- spring-mvc-handlerMapping 是怎么存放咱们的请求路径的-源码
- springmvc-执行流程
- spring-mvc 时如何选择 messageConverter
- springMVC-Interceptor-源码分析
本文应该是我计划spring-mvc的最后一篇,作一下几点说明
- 本文只对spring如何获取消息转换器(messageConverter)
- 具体的消息转换器是如何操做的不作详解
spring的消息处理器
- ByteArrayHttpMessageConverter
- StringHttpMessageConverter
- ResourceHttpMessageConverter
- ResourceRegionHttpMessageConverter
- SourceHttpMessageConverter
- AllEncompassingFormHttpMessageConverter
- MappingJackson2HttpMessageConverter
- Jaxb2RootElementHttpMessageConverter
咱们须要关注的消息处理器
- MappingJackson2HttpMessageConverter
- Jaxb2RootElementHttpMessageConverter
见名知意,上面的两个消息处理器是分别针对json,xmlspring
下面代码有部分若有不一样请看 spring-mcv执行流程express
public void invokeAndHandle(ServletWebRequest webRequest, ModelAndViewContainer mavContainer, Object... providedArgs) throws Exception {
//执行请求 returnValue 为响应值
Object returnValue = invokeForRequest(webRequest, mavContainer, providedArgs);
setResponseStatus(webRequest);
if (returnValue == null) {
if (isRequestNotModified(webRequest) || getResponseStatus() != null || mavContainer.isRequestHandled()) {
mavContainer.setRequestHandled(true);
return;
}
}
else if (StringUtils.hasText(getResponseStatusReason())) {
mavContainer.setRequestHandled(true);
return;
}
mavContainer.setRequestHandled(false);
Assert.state(this.returnValueHandlers != null, "No return value handlers");
try {
//在这个地方去作的 消息转换 spring 响应结果用的是输出流
this.returnValueHandlers.handleReturnValue(
returnValue, getReturnValueType(returnValue), mavContainer, webRequest);
}
catch (Exception ex) {
if (logger.isTraceEnabled()) {
logger.trace(formatErrorForReturnValue(returnValue), ex);
}
throw ex;
}
}
复制代码
@Override
public void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType, ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws IOException, HttpMediaTypeNotAcceptableException, HttpMessageNotWritableException {
mavContainer.setRequestHandled(true);
//获取流
ServletServerHttpRequest inputMessage = createInputMessage(webRequest);
ServletServerHttpResponse outputMessage = createOutputMessage(webRequest);
// Try even with null return value. ResponseBodyAdvice could get involved.
这里
writeWithMessageConverters(returnValue, returnType, inputMessage, outputMessage);
}
复制代码
@SuppressWarnings({"rawtypes", "unchecked"})
protected <T> void writeWithMessageConverters(@Nullable T value, MethodParameter returnType, ServletServerHttpRequest inputMessage, ServletServerHttpResponse outputMessage) throws IOException, HttpMediaTypeNotAcceptableException, HttpMessageNotWritableException {
Object body;
Class<?> valueType;
Type targetType;
//获取响应数据类型
if (value instanceof CharSequence) {
body = value.toString();
valueType = String.class;
targetType = String.class;
}
else {
body = value;
valueType = getReturnValueType(body, returnType);
targetType = GenericTypeResolver.resolveType(getGenericType(returnType), returnType.getContainingClass());
}
................................
MediaType selectedMediaType = null;
MediaType contentType = outputMessage.getHeaders().getContentType();
if (contentType != null && contentType.isConcrete()) {
if (logger.isDebugEnabled()) {
logger.debug("Found 'Content-Type:" + contentType + "' in response");
}
selectedMediaType = contentType;
}
else {
HttpServletRequest request = inputMessage.getServletRequest();
//获取客户端能够接受的 媒体类型
List<MediaType> acceptableTypes = getAcceptableMediaTypes(request);
//获取服务端能够处理的媒体类型 (重点)
List<MediaType> producibleTypes = getProducibleMediaTypes(request, valueType, targetType);
if (body != null && producibleTypes.isEmpty()) {
throw new HttpMessageNotWritableException(
"No converter found for return value of type: " + valueType);
}
List<MediaType> mediaTypesToUse = new ArrayList<>();
for (MediaType requestedType : acceptableTypes) {
for (MediaType producibleType : producibleTypes) {
if (requestedType.isCompatibleWith(producibleType)) {
mediaTypesToUse.add(getMostSpecificMediaType(requestedType, producibleType));
}
}
}
if (mediaTypesToUse.isEmpty()) {
if (body != null) {
throw new HttpMediaTypeNotAcceptableException(producibleTypes);
}
if (logger.isDebugEnabled()) {
logger.debug("No match for " + acceptableTypes + ", supported: " + producibleTypes);
}
return;
}
MediaType.sortBySpecificityAndQuality(mediaTypesToUse);
//肯定最后使用的媒体类型,debug 你会发现 只要存在 xml 的媒体类型,则使用xml,没有的话才会考虑json,他们直接存在一个顺序的问题
for (MediaType mediaType : mediaTypesToUse) {
if (mediaType.isConcrete()) {
selectedMediaType = mediaType;
break;
}
else if (mediaType.equals(MediaType.ALL) || mediaType.equals(MEDIA_TYPE_APPLICATION)) {
selectedMediaType = MediaType.APPLICATION_OCTET_STREAM;
break;
}
}
if (logger.isDebugEnabled()) {
logger.debug("Using '" + selectedMediaType + "', given " +
acceptableTypes + " and supported " + producibleTypes);
}
}
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)) {
//处理消息
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 {
// 使用输出流 写出结果
((HttpMessageConverter) converter).write(body, selectedMediaType, outputMessage);
}
}
else {
if (logger.isDebugEnabled()) {
logger.debug("Nothing to write: null body");
}
}
return;
}
}
}
if (body != null) {
throw new HttpMediaTypeNotAcceptableException(this.allSupportedMediaTypes);
}
}
复制代码
重点看下怎么获取服务端支持的媒体类型json
//关键就是这句代码
List<MediaType> producibleTypes = getProducibleMediaTypes(request, valueType, targetType);
复制代码
本身总结的三种状况spring-mvc
没有指定响应媒体类型(spring默认)
protected List<MediaType> getProducibleMediaTypes( HttpServletRequest request, Class<?> valueClass, @Nullable Type targetType) {
//假如使用@RequestMapping指定了 mediaTypes 则存在值 下面会讲
Set<MediaType> mediaTypes =
(Set<MediaType>) request.getAttribute(HandlerMapping.PRODUCIBLE_MEDIA_TYPES_ATTRIBUTE);
if (!CollectionUtils.isEmpty(mediaTypes)) {
return new ArrayList<>(mediaTypes);
}
else if (!this.allSupportedMediaTypes.isEmpty()) {
//假如没指定
List<MediaType> result = new ArrayList<>();
//this.messageConverters没指定全局的话为 7种 包含 MappingJackson2HttpMessageConverter Jaxb2RootElementHttpMessageConverter
for (HttpMessageConverter<?> converter : this.messageConverters) {
if (converter instanceof GenericHttpMessageConverter && targetType != null) {
if (((GenericHttpMessageConverter<?>) converter).canWrite(targetType, valueClass, null)) {
result.addAll(converter.getSupportedMediaTypes());
}
}
else if (converter.canWrite(valueClass, null)) {
result.addAll(converter.getSupportedMediaTypes());
}
}
//假如响应的类型存在@XmlRootElement 返回的结果为:
//1.application/xml
//2.text/xml
//3.application/*+xml
//4.application/json
//5.application/*+json
//注意存在一个顺序问题,假如存在xml xml必在前面
//假如响应的类型不存在@XmlRootElement 返回的结果为:
//1.application/json
//2.application/*+json
//总结下的意思就是 : 返回值类型是被@XmlRootElement 注释的的话 当作xml处理的 反之为json,在根据这个返回获取messageConverter 使用的获取添加为converter.canWrite(valueClass, null)
return result;
}
else {
return Collections.singletonList(MediaType.ALL);
}
}
复制代码
使用@RequestMapping(valeu="XXX" produces = MediaType.APPLICATION_XML_VALUE)
@SuppressWarnings("unchecked")
protected List<MediaType> getProducibleMediaTypes( HttpServletRequest request, Class<?> valueClass, @Nullable Type targetType) {
//使用了@RequestMapping 指定的话 直接返回mediaTypes ,因此说咱们就看下mediaTypes的值是从哪里取到的就能够了
Set<MediaType> mediaTypes =
(Set<MediaType>) request.getAttribute(HandlerMapping.PRODUCIBLE_MEDIA_TYPES_ATTRIBUTE);
............................................................................
}
复制代码
@Override
public Object getAttribute(String name) {
if (request == null) {
throw new IllegalStateException(
sm.getString("requestFacade.nullRequest"));
}
//会发现是从request.attribute 中那的值,attribute就是一个map
//org.springframework.web.servlet.HandlerMapping.producibleMediaTypes 为key
//如今就去看看attribute是在何时存在的这个键值对
return request.getAttribute(name);
}
复制代码
Attribute 存放媒体类型的键值对是在 handlerMethod 的过程当中从 RequestMappingInfo 中获取到的,假如对spring如何获取 handlerMethod 不了解的话能够看下 spring-mvc-handlerMapping 是怎么存放咱们的请求路径的-源码mvc
@Nullable
protected HandlerMethod lookupHandlerMethod(String lookupPath, HttpServletRequest request) throws Exception {
List<Match> matches = new ArrayList<>();
List<T> directPathMatches = this.mappingRegistry.getMappingsByUrl(lookupPath);
if (directPathMatches != null) {
addMatchingMappings(directPathMatches, matches, request);
}
if (matches.isEmpty()) {
// No choice but to go through all mappings...
addMatchingMappings(this.mappingRegistry.getMappings().keySet(), matches, request);
}
if (!matches.isEmpty()) {
Comparator<Match> comparator = new MatchComparator(getMappingComparator(request));
matches.sort(comparator);
Match bestMatch = matches.get(0);
if (matches.size() > 1) {
if (logger.isTraceEnabled()) {
logger.trace(matches.size() + " matching mappings: " + matches);
}
if (CorsUtils.isPreFlightRequest(request)) {
return PREFLIGHT_AMBIGUOUS_MATCH;
}
Match secondBestMatch = matches.get(1);
if (comparator.compare(bestMatch, secondBestMatch) == 0) {
Method m1 = bestMatch.handlerMethod.getMethod();
Method m2 = secondBestMatch.handlerMethod.getMethod();
String uri = request.getRequestURI();
throw new IllegalStateException(
"Ambiguous handler methods mapped for '" + uri + "': {" + m1 + ", " + m2 + "}");
}
}
request.setAttribute(BEST_MATCHING_HANDLER_ATTRIBUTE, bestMatch.handlerMethod);
// 这个地方 去获取的 媒体类型
handleMatch(bestMatch.mapping, lookupPath, request);
return bestMatch.handlerMethod;
}
else {
return handleNoMatch(this.mappingRegistry.getMappings().keySet(), lookupPath, request);
}
}
复制代码
@Override
protected void handleMatch(RequestMappingInfo info, String lookupPath, HttpServletRequest request) {
super.handleMatch(info, lookupPath, request);
................................................................................
if (!info.getProducesCondition().getProducibleMediaTypes().isEmpty()) {
//获取到指定的媒体类型
Set<MediaType> mediaTypes = info.getProducesCondition().getProducibleMediaTypes();
//放入 Attribute key 为 org.springframework.web.servlet.HandlerMapping.producibleMediaTypes
request.set Attribute (PRODUCIBLE_MEDIA_TYPES_ATTRIBUTE, mediaTypes);
}
}
复制代码
能够看出媒体类型是在 RequestMappingInfo.getProducesCondition().getProducibleMediaTypes 中获取的app
而后前面几篇文章都讲过 RequestMappingInfo 是在 requestMappingHandlerMapping 初始化的过程当中出现的ide
假若有能够看下前面的几篇文源码分析
//这段代码是 获取 handlerMethod 中的一个片断
protected RequestMappingInfo getMappingForMethod(Method method, Class<?> handlerType) {
RequestMappingInfo info = createRequestMappingInfo(method);
if (info != null) {
//建立RequestMappingInfo
RequestMappingInfo typeInfo = createRequestMappingInfo(handlerType);
if (typeInfo != null) {
info = typeInfo.combine(info);
}
String prefix = getPathPrefix(handlerType);
if (prefix != null) {
info = RequestMappingInfo.paths(prefix).build().combine(info);
}
}
return info;
}
复制代码
@Nullable
private RequestMappingInfo createRequestMappingInfo(AnnotatedElement element) {
//获取 一些值 包括 媒体类型
//这个方法是获取@RequestMapping 注解的值,咱们其中就包含了咱们今天讲的 返回值类型 xml ? json
//里面东西挺多的不看了,只要知道是获取注解值的就好了
RequestMapping requestMapping = AnnotatedElementUtils.findMergedAnnotation(element, RequestMapping.class);
RequestCondition<?> condition = (element instanceof Class ?
getCustomTypeCondition((Class<?>) element) : getCustomMethodCondition((Method) element));
//建立 RequestMappingInfo 点进去会返现 媒体类型的值是从requestMapping中取的
return (requestMapping != null ? createRequestMappingInfo(requestMapping, condition) : null);
}
复制代码
使用全局变量设置及重写WebMvcConfigurationSupport.configureMessageConverters()方法(正常项目都是会这么作的)
先看两段代码,在上面都出现过的代码
@SuppressWarnings("unchecked")
protected List<MediaType> getProducibleMediaTypes( HttpServletRequest request, Class<?> valueClass, @Nullable Type targetType) {
//处理第一种请款的,上面讲过了
Set<MediaType> mediaTypes =
(Set<MediaType>) request.getAttribute(HandlerMapping.PRODUCIBLE_MEDIA_TYPES_ATTRIBUTE);
if (!CollectionUtils.isEmpty(mediaTypes)) {
return new ArrayList<>(mediaTypes);
}
//处理第二种第三种状况的,是这个
//首先有两个概念
//1.MediaType 媒体类型(这是我直译够来的,也不知作别人怎么称呼的)
//2.HttpMessageConverter 消息转换器
//而后
//在没有定义全局指定的状况下 messageConverters 为 8种
//假如重写了org.springframework.web.servlet.config.annotation.WebMvcConfigurationSupport.configureMessageConverters的状况下 messageConverters的值为你本身添加的
//咱们最后是要拿到合适的消息处理器(messageConverter)
//阅读writeWithMessageConverters方法咱们会发现咱们要获取的消息处理器是根据媒体类型判断的
//根据媒体类型去 messageConverters 取消息处理器,你想下假如你只配置了一个json的,无论媒体类型有多少是否是只能为json'的处理器
//因此说总结下,能够这么说:
//1.假如没有配置全局的(messageConverters里面有8种) 是根据媒体类型
//2.假如配置了全局的,是根据你配置的和媒体类型,假如最后找不到会报错
else if (!this.allSupportedMediaTypes.isEmpty()) {
List<MediaType> result = new ArrayList<>();
for (HttpMessageConverter<?> converter : this.messageConverters) {
if (converter instanceof GenericHttpMessageConverter && targetType != null) {
if (((GenericHttpMessageConverter<?>) converter).canWrite(targetType, valueClass, null)) {
result.addAll(converter.getSupportedMediaTypes());
}
}
else if (converter.canWrite(valueClass, null)) {
result.addAll(converter.getSupportedMediaTypes());
}
}
return result;
}
else {
return Collections.singletonList(MediaType.ALL);
}
}
复制代码
@SuppressWarnings({"rawtypes", "unchecked"})
protected <T> void writeWithMessageConverters(@Nullable T value, MethodParameter returnType, ServletServerHttpRequest inputMessage, ServletServerHttpResponse outputMessage) throws IOException, HttpMediaTypeNotAcceptableException, HttpMessageNotWritableException {
....................................................
MediaType selectedMediaType = null;
MediaType contentType = outputMessage.getHeaders().getContentType();
//客户端直接在请求头中定义声明了使用哪一个返回类型,那就直接使用
if (contentType != null && contentType.isConcrete()) {
if (logger.isDebugEnabled()) {
logger.debug("Found 'Content-Type:" + contentType + "' in response");
}
selectedMediaType = contentType;
}
else {
HttpServletRequest request = inputMessage.getServletRequest();
List<MediaType> acceptableTypes = getAcceptableMediaTypes(request);
//获取咱们服务端支持的媒体类型
List<MediaType> producibleTypes = getProducibleMediaTypes(request, valueType, targetType);
if (body != null && producibleTypes.isEmpty()) {
throw new HttpMessageNotWritableException(
"No converter found for return value of type: " + valueType);
}
List<MediaType> mediaTypesToUse = new ArrayList<>();
for (MediaType requestedType : acceptableTypes) {
for (MediaType producibleType : producibleTypes) {
if (requestedType.isCompatibleWith(producibleType)) {
mediaTypesToUse.add(getMostSpecificMediaType(requestedType, producibleType));
}
}
}
if (mediaTypesToUse.isEmpty()) {
if (body != null) {
throw new HttpMediaTypeNotAcceptableException(producibleTypes);
}
if (logger.isDebugEnabled()) {
logger.debug("No match for " + acceptableTypes + ", supported: " + producibleTypes);
}
return;
}
MediaType.sortBySpecificityAndQuality(mediaTypesToUse);
//循环 getProducibleMediaTypes 中获取的媒体类型 顺序 假若有xml 就必定使用xml
for (MediaType mediaType : mediaTypesToUse) {
if (mediaType.isConcrete()) {
selectedMediaType = mediaType;
break;
}
else if (mediaType.equals(MediaType.ALL) || mediaType.equals(MEDIA_TYPE_APPLICATION)) {
selectedMediaType = MediaType.APPLICATION_OCTET_STREAM;
break;
}
}
}
if (selectedMediaType != null) {
selectedMediaType = selectedMediaType.removeQualityValue();
for (HttpMessageConverter<?> converter : this.messageConverters) {
GenericHttpMessageConverter genericConverter = (converter instanceof GenericHttpMessageConverter ?
(GenericHttpMessageConverter<?>) converter : null);
//这里也是使用canWrite进行判断是否合适
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);
...............................................
return;
}
}
}
}
复制代码
我感受上面的代码我应该讲的比较清晰了
如今去看下messageConverters的值是在何时被赋值的
RequestMappingHandlerAdapter初始化的过程完成的messageConverters的赋值
public void afterPropertiesSet() {
// Do this first, it may add ResponseBody advice beans
initControllerAdviceCache();
if (this.argumentResolvers == null) {
//这里
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);
}
}
private List<HandlerMethodArgumentResolver> getDefaultArgumentResolvers() {
List<HandlerMethodArgumentResolver> resolvers = new ArrayList<>();
// Annotation-based argument resolution
resolvers.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));
//这里
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());
.........................................................
return resolvers;
}
复制代码
在afterPropertiesSet只是一些传递值的过程,仍是没有找到数据源,那咱们去看看RequestMappingHandlerAdapter实例化的过程
@Bean
public RequestMappingHandlerAdapter requestMappingHandlerAdapter() {
//建立 RequestMappingHandlerAdapter 这个时候其实使用四个默认的 消息转换器的
RequestMappingHandlerAdapter adapter = createRequestMappingHandlerAdapter();
adapter.setContentNegotiationManager(mvcContentNegotiationManager());
//这里很关键
adapter.setMessageConverters(getMessageConverters());
adapter.setWebBindingInitializer(getConfigurableWebBindingInitializer());
adapter.setCustomArgumentResolvers(getArgumentResolvers());
adapter.setCustomReturnValueHandlers(getReturnValueHandlers());
...........................................................................
return adapter;
}
复制代码
protected final List<HttpMessageConverter<?>> getMessageConverters() {
if (this.messageConverters == null) {
this.messageConverters = new ArrayList<>();
//调用咱们重写的方法 也就是我本文说的指定的全局
configureMessageConverters(this.messageConverters);
if (this.messageConverters.isEmpty()) {
//假如不存在,再去加载全部的默认的
addDefaultHttpMessageConverters(this.messageConverters);
}
extendMessageConverters(this.messageConverters);
}
return this.messageConverters;
}
复制代码
总结
- 没有指定响应媒体类型
- xml:
- 处理器
- Jaxb2RootElementHttpMessageConverter
- MappingJackson2HttpMessageConverter 2.媒体类型
- application/xml
- text/xml
- application/*+xml
- application/json
- application/*+json
- 处理器
- json:
- 处理器:
- MappingJackson2HttpMessageConverter
- 媒体类型:
- application/json
- application/*+json
- 处理器:
- xml:
- 使用方法注解@RequestMapping指定
- 执行的时候媒体类型是在reques.attribute中拿的数据
- reques.attribute 是在获取handlerMethod的过程当中被赋值的,数据源在handlerMethod.RequestMappingInfo.producesCondtion.expressions 中保存的
- expressions是在 handlerMappingRequestMapping 初始的过程当中 建立的 RequestMappingInfo 的时候,从方法注解上解析出来的
- 使用全局
- 直接指定处理器
- 假如指定了全局,再去指定不一样的局部(方法上执行) 会报错
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