spring-浅析加载消息转换器,处理@Responsebody注解
简要分析spring加载消息转换器,处理@Responsebody注解的controller,
并且也是添加jackson-dataformat-xml依赖之后,bean转化为xml字符串.
参考文章:
https://blog.csdn.net/sunroyfcb/article/details/81048675
https://www.jianshu.com/p/0a9c247571f9
https://www.jianshu.com/p/0aaeb4144489
添加此依赖可实现@Responsebody注解的接口,
返回类型如果是bean,实现bean->xml的转化,不再是bean->json:
com.fasterxml.jackson.dataformat
jackson-dataformat-xml
2.9.6
加载消息转换器:
-------idea中ctrl+n可以搜索源码中的类
在WebMvcConfigurationSupport类中
1.加载消息转换器addDefaultHttpMessageConverters方法:
protected final void addDefaultHttpMessageConverters(List> messageConverters) {
StringHttpMessageConverter stringHttpMessageConverter = new StringHttpMessageConverter();
stringHttpMessageConverter.setWriteAcceptCharset(false); // see SPR-7316
messageConverters.add(new ByteArrayHttpMessageConverter());
messageConverters.add(stringHttpMessageConverter);
messageConverters.add(new ResourceHttpMessageConverter());
messageConverters.add(new ResourceRegionHttpMessageConverter());
messageConverters.add(new SourceHttpMessageConverter<>());
messageConverters.add(new AllEncompassingFormHttpMessageConverter());
if (romePresent) {
messageConverters.add(new AtomFeedHttpMessageConverter());
messageConverters.add(new RssChannelHttpMessageConverter());
}
// 加载xml消息转换器
if (jackson2XmlPresent) {
Jackson2ObjectMapperBuilder builder = Jackson2ObjectMapperBuilder.xml();
if (this.applicationContext != null) {
builder.applicationContext(this.applicationContext);
}
messageConverters.add(new MappingJackson2XmlHttpMessageConverter(builder.build()));
}
else if (jaxb2Present) {
messageConverters.add(new Jaxb2RootElementHttpMessageConverter());
}
// 加载json消息转换器
if (jackson2Present) {
Jackson2ObjectMapperBuilder builder = Jackson2ObjectMapperBuilder.json();
if (this.applicationContext != null) {
builder.applicationContext(this.applicationContext);
}
messageConverters.add(new MappingJackson2HttpMessageConverter(builder.build()));
}
else if (gsonPresent) {
messageConverters.add(new GsonHttpMessageConverter());
}
else if (jsonbPresent) {
messageConverters.add(new JsonbHttpMessageConverter());
}
if (jackson2SmilePresent) {
Jackson2ObjectMapperBuilder builder = Jackson2ObjectMapperBuilder.smile();
if (this.applicationContext != null) {
builder.applicationContext(this.applicationContext);
}
messageConverters.add(new MappingJackson2SmileHttpMessageConverter(builder.build()));
}
if (jackson2CborPresent) {
Jackson2ObjectMapperBuilder builder = Jackson2ObjectMapperBuilder.cbor();
if (this.applicationContext != null) {
builder.applicationContext(this.applicationContext);
}
messageConverters.add(new MappingJackson2CborHttpMessageConverter(builder.build()));
}
}
其中jackson2XmlPresent表示是否加载了com.fasterxml.jackson.dataformat.xml.XmlMapper,
jackson2XmlPresent=true表示支持对xml与bean之间的转换.即:加载MappingJackson2XmlHttpMessageConverter转换器
2.创建HandlerExceptionResolver对象bean
@Bean
public HandlerExceptionResolver handlerExceptionResolver() {
List exceptionResolvers = new ArrayList<>();
configureHandlerExceptionResolvers(exceptionResolvers);
if (exceptionResolvers.isEmpty()) {
addDefaultHandlerExceptionResolvers(exceptionResolvers);
}
extendHandlerExceptionResolvers(exceptionResolvers);
HandlerExceptionResolverComposite composite = new HandlerExceptionResolverComposite();
composite.setOrder(0);
composite.setExceptionResolvers(exceptionResolvers);
return composite;
}
进入addDefaultHandlerExceptionResolvers:
protected final void addDefaultHandlerExceptionResolvers(List exceptionResolvers) {
ExceptionHandlerExceptionResolver exceptionHandlerResolver = createExceptionHandlerExceptionResolver();
exceptionHandlerResolver.setContentNegotiationManager(mvcContentNegotiationManager());
// // 获取并set消息转换器
exceptionHandlerResolver.setMessageConverters(getMessageConverters());
exceptionHandlerResolver.setCustomArgumentResolvers(getArgumentResolvers());
exceptionHandlerResolver.setCustomReturnValueHandlers(getReturnValueHandlers());
if (jackson2Present) {
exceptionHandlerResolver.setResponseBodyAdvice(
Collections.singletonList(new JsonViewResponseBodyAdvice()));
}
if (this.applicationContext != null) {
exceptionHandlerResolver.setApplicationContext(this.applicationContext);
}
exceptionHandlerResolver.afterPropertiesSet();
exceptionResolvers.add(exceptionHandlerResolver);
ResponseStatusExceptionResolver responseStatusResolver = new ResponseStatusExceptionResolver();
responseStatusResolver.setMessageSource(this.applicationContext);
exceptionResolvers.add(responseStatusResolver);
exceptionResolvers.add(new DefaultHandlerExceptionResolver());
}
进入getMessageConverters方法:
protected final List> getMessageConverters() {
// 消息转换器为空,未加载, 调用addDefaultHttpMessageConverters 加载消息转换器,
// 否则直接返回已加载完成的消息转换器
if (this.messageConverters == null) {
this.messageConverters = new ArrayList<>();
configureMessageConverters(this.messageConverters);
if (this.messageConverters.isEmpty()) {
addDefaultHttpMessageConverters(this.messageConverters);
}
extendMessageConverters(this.messageConverters);
}
return this.messageConverters;
}
3创建RequestMappingHandlerAdapter(处理器适配器)对象:
@Bean
public RequestMappingHandlerAdapter requestMappingHandlerAdapter() {
RequestMappingHandlerAdapter adapter = createRequestMappingHandlerAdapter();
adapter.setContentNegotiationManager(mvcContentNegotiationManager());
// 获取并set消息转换器
adapter.setMessageConverters(getMessageConverters());
adapter.setWebBindingInitializer(getConfigurableWebBindingInitializer());
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;
}
RequestMappingHandlerAdapter类实现了InitializingBean接口,
所以必须实现InitializingBean接口的afterPropertiesSet方法
afterPropertiesSet()方法将在spring加载完InitializingBean接口实现类之后自动调用
@Override
public void afterPropertiesSet() {
// Do this first, it may add ResponseBody advice beans
initControllerAdviceCache();
if (this.argumentResolvers == null) {
List resolvers = getDefaultArgumentResolvers();
this.argumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers);
}
if (this.initBinderArgumentResolvers == null) {
List resolvers = getDefaultInitBinderArgumentResolvers();
this.initBinderArgumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers);
}
if (this.returnValueHandlers == null) {
// 获取返回值的处理器
List handlers = getDefaultReturnValueHandlers();
this.returnValueHandlers = new HandlerMethodReturnValueHandlerComposite().addHandlers(handlers);
}
}
private List getDefaultReturnValueHandlers() {
List handlers = new ArrayList<>();
// Single-purpose return value types
handlers.add(new ModelAndViewMethodReturnValueHandler());
handlers.add(new ModelMethodProcessor());
handlers.add(new ViewMethodReturnValueHandler());
handlers.add(new ResponseBodyEmitterReturnValueHandler(getMessageConverters(),
this.reactiveAdapterRegistry, this.taskExecutor, this.contentNegotiationManager));
handlers.add(new StreamingResponseBodyReturnValueHandler());
handlers.add(new HttpEntityMethodProcessor(getMessageConverters(),
this.contentNegotiationManager, this.requestResponseBodyAdvice));
handlers.add(new HttpHeadersReturnValueHandler());
handlers.add(new CallableMethodReturnValueHandler());
handlers.add(new DeferredResultMethodReturnValueHandler());
handlers.add(new AsyncTaskMethodReturnValueHandler(this.beanFactory));
// Annotation-based return value types
handlers.add(new ModelAttributeMethodProcessor(false));
// ResponseBody处理器,并设置加载的消息处理器getMessageConverters
handlers.add(new RequestResponseBodyMethodProcessor(getMessageConverters(),
this.contentNegotiationManager, this.requestResponseBodyAdvice));
// Multi-purpose return value types
handlers.add(new ViewNameMethodReturnValueHandler());
handlers.add(new MapMethodProcessor());
// Custom return value types
if (getCustomReturnValueHandlers() != null) {
handlers.addAll(getCustomReturnValueHandlers());
}
// Catch-all
if (!CollectionUtils.isEmpty(getModelAndViewResolvers())) {
handlers.add(new ModelAndViewResolverMethodReturnValueHandler(getModelAndViewResolvers()));
}
else {
handlers.add(new ModelAttributeMethodProcessor(true));
}
return handlers;
}
RequestResponseBodyMethodProcessor继承AbstractMessageConverterMethodProcessor
返回消息处理:
若是@Responsebody注解的mapping,则选取消息转换器:
AbstractMessageConverterMethodProcessor中:
核心代码:
这里分析的是加入jackson-dataformat-xml依赖
protected void writeWithMessageConverters(@Nullable T value, MethodParameter returnType,
ServletServerHttpRequest inputMessage, ServletServerHttpResponse outputMessage)
throws IOException, HttpMediaTypeNotAcceptableException, HttpMessageNotWritableException {
Object outputValue;
Class valueType;
Type declaredType;
if (value instanceof CharSequence) {
outputValue = value.toString();
valueType = String.class;
declaredType = String.class;
}
else {
outputValue = value;
valueType = getReturnValueType(outputValue, returnType);
declaredType = getGenericType(returnType);
}
if (isResourceType(value, returnType)) {
outputMessage.getHeaders().set(HttpHeaders.ACCEPT_RANGES, "bytes");
if (value != null && inputMessage.getHeaders().getFirst(HttpHeaders.RANGE) != null) {
Resource resource = (Resource) value;
try {
List httpRanges = inputMessage.getHeaders().getRange();
outputMessage.getServletResponse().setStatus(HttpStatus.PARTIAL_CONTENT.value());
outputValue = HttpRange.toResourceRegions(httpRanges, resource);
valueType = outputValue.getClass();
declaredType = RESOURCE_REGION_LIST_TYPE;
}
catch (IllegalArgumentException ex) {
outputMessage.getHeaders().set(HttpHeaders.CONTENT_RANGE, "bytes */" + resource.contentLength());
outputMessage.getServletResponse().setStatus(HttpStatus.REQUESTED_RANGE_NOT_SATISFIABLE.value());
}
}
}
List mediaTypesToUse;
MediaType contentType = outputMessage.getHeaders().getContentType();
if (contentType != null && contentType.isConcrete()) {
mediaTypesToUse = Collections.singletonList(contentType);
}
else {
HttpServletRequest request = inputMessage.getServletRequest();
List requestedMediaTypes = getAcceptableMediaTypes(request);
// 1. 获取该请求的MediaTypes, 没有设置的话返回消息处理器支持的MediaTypes
List producibleMediaTypes = getProducibleMediaTypes(request, valueType, declaredType);
if (outputValue != null && producibleMediaTypes.isEmpty()) {
throw new HttpMessageNotWritableException(
"No converter found for return value of type: " + valueType);
}
mediaTypesToUse = new ArrayList<>();
for (MediaType requestedType : requestedMediaTypes) {
for (MediaType producibleType : producibleMediaTypes) {
if (requestedType.isCompatibleWith(producibleType)) {
mediaTypesToUse.add(getMostSpecificMediaType(requestedType, producibleType));
}
}
}
if (mediaTypesToUse.isEmpty()) {
if (outputValue != null) {
throw new HttpMediaTypeNotAcceptableException(producibleMediaTypes);
}
return;
}
// 排序 todo
MediaType.sortBySpecificityAndQuality(mediaTypesToUse);
}
// 2.将会获得 application/xml
MediaType selectedMediaType = null;
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);
if (genericConverter != null ?
((GenericHttpMessageConverter) converter).canWrite(declaredType, valueType, selectedMediaType) :
converter.canWrite(valueType, selectedMediaType)) {
// 3. 会由MappingJackson2XmlHttpMessageConverter解析器处理返回body
outputValue = getAdvice().beforeBodyWrite(outputValue, returnType, selectedMediaType,
(Class>) converter.getClass(),
inputMessage, outputMessage);
if (outputValue != null) {
addContentDispositionHeader(inputMessage, outputMessage);
if (genericConverter != null) {
genericConverter.write(outputValue, declaredType, selectedMediaType, outputMessage);
}
else {
((HttpMessageConverter) converter).write(outputValue, selectedMediaType, outputMessage);
}
if (logger.isDebugEnabled()) {
logger.debug("Written [" + outputValue + "] as \"" + selectedMediaType +
"\" using [" + converter + "]");
}
}
return;
}
}
}
if (outputValue != null) {
throw new HttpMediaTypeNotAcceptableException(this.allSupportedMediaTypes);
}
}
获取请求MediaTypes源码:
protected List getProducibleMediaTypes(
HttpServletRequest request, Class valueClass, @Nullable Type declaredType) {
Set mediaTypes =
(Set) request.getAttribute(HandlerMapping.PRODUCIBLE_MEDIA_TYPES_ATTRIBUTE);
if (!CollectionUtils.isEmpty(mediaTypes)) {
return new ArrayList<>(mediaTypes);
}
// 没有produces属性走else, 此时会加载MappingJackson2XmlHttpMessageConverter,MappingJackson2HttpMessageConverter
// 并且MappingJackson2XmlHttpMessageConverter支持:application/xml,text/xml,application/*+xml
// 而MappingJackson2HttpMessageConverter支持: application/json, application/*+json
else if (!this.allSupportedMediaTypes.isEmpty()) {
List result = new ArrayList<>();
for (HttpMessageConverter converter : this.messageConverters) {
if (converter instanceof GenericHttpMessageConverter && declaredType != null) {
if (((GenericHttpMessageConverter) converter).canWrite(declaredType, valueClass, null)) {
result.addAll(converter.getSupportedMediaTypes());
}
}
else if (converter.canWrite(valueClass, null)) {
result.addAll(converter.getSupportedMediaTypes());
}
}
return result;
}
else {
return Collections.singletonList(MediaType.ALL);
}
}
在这个方法writeWithMessageConverters就将bean返回为xml了…
问题1:
首先添加上面com.fasterxml.jackson.dataformat依赖,然而添加@ResponseBody注解的接口返回对象还是转化为json,而不是xml
答:
1.在项目中配置了拦截器,拦截器继承的是:WebMvcConfigurerAdapter类
只需要改为 WebMvcConfigurationSupport
2. @RequestMapping配置了produces属性值为application/json
问题2:
添加上面com.fasterxml.jackson.dataformat依赖之后为什么
添加@ResponseBody注解的controller返回bean对象时客户端接收到的是xml,而不是json?
答:
在@RequestMapping没有配置produces情况下, 起初返回json是因为消息返回解析器为MappingJackson2HttpMessageConverter,
当引入com.fasterxml.jackson.dataformat依赖之后,消息返回解析器为MappingJackson2XmlHttpMessageConverter