问题背景：如题。
问题定位：代码跟踪，从源头入手，一步一步跟进，直到设置中文编码的地方。
问题代码：
/** * 获取单个测试桩接口内容 * * @author wulinfeng * @param method * @return */ @RequestMapping(value = "/getMethod/{method}", method = RequestMethod.GET) public @ResponseBody String getMethodContent(@PathVariable("method") String method) { return testPillingService.getMethodContent(method); }
怎么切入？是个问题。既然是从源头跟起，那么还是拿DispatcherServlet来开刀吧。所有Controller请求都不可避免的要到这个请求集散地来，而这里最主要的就是doDispatch方法了：
/** * Process the actual dispatching to the handler. * <p>The handler will be obtained by applying the servlet's HandlerMappings in order. * The HandlerAdapter will be obtained by querying the servlet's installed HandlerAdapters * to find the first that supports the handler class. * <p>All HTTP methods are handled by this method. It's up to HandlerAdapters or handlers * themselves to decide which methods are acceptable. * @param request current HTTP request * @param response current HTTP response * @throws Exception in case of any kind of processing failure */ protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception { HttpServletRequest processedRequest = request; HandlerExecutionChain mappedHandler = null; boolean multipartRequestParsed = false; WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request); try { ModelAndView mv = null; Exception dispatchException = null; try { processedRequest = checkMultipart(request); multipartRequestParsed = (processedRequest != request); // Determine handler for the current request. mappedHandler = getHandler(processedRequest); if (mappedHandler == null || mappedHandler.getHandler() == null) { noHandlerFound(processedRequest, response); return; } // Determine handler adapter for the current request. HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler()); // Process last-modified header, if supported by the handler. String method = request.getMethod(); boolean isGet = "GET".equals(method); if (isGet || "HEAD".equals(method)) { long lastModified = ha.getLastModified(request, mappedHandler.getHandler()); if (logger.isDebugEnabled()) { logger.debug("Last-Modified value for [" + getRequestUri(request) + "] is: " + lastModified); } if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) { return; } } if (!mappedHandler.applyPreHandle(processedRequest, response)) { return; } // Actually invoke the handler. mv = ha.handle(processedRequest, response, mappedHandler.getHandler()); if (asyncManager.isConcurrentHandlingStarted()) { return; } applyDefaultViewName(processedRequest, mv); mappedHandler.applyPostHandle(processedRequest, response, mv); } catch (Exception ex) { dispatchException = ex; } processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException); } catch (Exception ex) { triggerAfterCompletion(processedRequest, response, mappedHandler, ex); } catch (Throwable err) { triggerAfterCompletionWithError(processedRequest, response, mappedHandler, err); } finally { if (asyncManager.isConcurrentHandlingStarted()) { // Instead of postHandle and afterCompletion if (mappedHandler != null) { mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response); } } else { // Clean up any resources used by a multipart request. if (multipartRequestParsed) { cleanupMultipart(processedRequest); } } } }
看961行，得到了请求参数、请求url映射的处理器、处理的适配器后，进入真正的请求处理流程。先到AbstractHandlerMethodAdapter类，再到子类RequestMappingHandlerAdapter里
protected ModelAndView handleInternal(HttpServletRequest request, HttpServletResponse response, HandlerMethod handlerMethod) throws Exception { ModelAndView mav; checkRequest(request); // Execute invokeHandlerMethod in synchronized block if required. if (this.synchronizeOnSession) { HttpSession session = request.getSession(false); if (session != null) { Object mutex = WebUtils.getSessionMutex(session); synchronized (mutex) { mav = invokeHandlerMethod(request, response, handlerMethod); } } else { // No HttpSession available -> no mutex necessary mav = invokeHandlerMethod(request, response, handlerMethod); } } else { // No synchronization on session demanded at all... mav = invokeHandlerMethod(request, response, handlerMethod); } if (!response.containsHeader(HEADER_CACHE_CONTROL)) { if (getSessionAttributesHandler(handlerMethod).hasSessionAttributes()) { applyCacheSeconds(response, this.cacheSecondsForSessionAttributeHandlers); } else { prepareResponse(response); } } return mav; }
protected ModelAndView invokeHandlerMethod(HttpServletRequest request, HttpServletResponse response, HandlerMethod handlerMethod) throws Exception { ServletWebRequest webRequest = new ServletWebRequest(request, response); WebDataBinderFactory binderFactory = getDataBinderFactory(handlerMethod); ModelFactory modelFactory = getModelFactory(handlerMethod, binderFactory); ServletInvocableHandlerMethod invocableMethod = createInvocableHandlerMethod(handlerMethod); invocableMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers); 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); if (asyncManager.hasConcurrentResult()) { Object result = asyncManager.getConcurrentResult(); mavContainer = (ModelAndViewContainer) asyncManager.getConcurrentResultContext()[0]; asyncManager.clearConcurrentResult(); if (logger.isDebugEnabled()) { logger.debug("Found concurrent result value [" + result + "]"); } invocableMethod = invocableMethod.wrapConcurrentResult(result); } invocableMethod.invokeAndHandle(webRequest, mavContainer); if (asyncManager.isConcurrentHandlingStarted()) { return null; } return getModelAndView(mavContainer, modelFactory, webRequest); }
进入RequestMappingHandlerAdapter类832行，我们终于到了把处理响应的地方了，接着看ServletInvocableHandlerMethod类107行
public void invokeAndHandle(ServletWebRequest webRequest, ModelAndViewContainer mavContainer, Object... providedArgs) throws Exception { Object returnValue = invokeForRequest(webRequest, mavContainer, providedArgs); setResponseStatus(webRequest); if (returnValue == null) { if (isRequestNotModified(webRequest) || hasResponseStatus() || mavContainer.isRequestHandled()) { mavContainer.setRequestHandled(true); return; } } else if (StringUtils.hasText(this.responseReason)) { mavContainer.setRequestHandled(true); return; } mavContainer.setRequestHandled(false); try { this.returnValueHandlers.handleReturnValue( returnValue, getReturnValueType(returnValue), mavContainer, webRequest); } catch (Exception ex) { if (logger.isTraceEnabled()) { logger.trace(getReturnValueHandlingErrorMessage("Error handling return value", returnValue), ex); } throw ex; } }
InvocableHandlerMethod类主要是通过反射来调用Controller方法的
/** * Invoke the method after resolving its argument values in the context of the given request. * <p>Argument values are commonly resolved through {@link HandlerMethodArgumentResolver}s. * The {@code providedArgs} parameter however may supply argument values to be used directly, * i.e. without argument resolution. Examples of provided argument values include a * {@link WebDataBinder}, a {@link SessionStatus}, or a thrown exception instance. * Provided argument values are checked before argument resolvers. * @param request the current request * @param mavContainer the ModelAndViewContainer for this request * @param providedArgs "given" arguments matched by type, not resolved * @return the raw value returned by the invoked method * @exception Exception raised if no suitable argument resolver can be found, * or if the method raised an exception */ public Object invokeForRequest(NativeWebRequest request, ModelAndViewContainer mavContainer, Object... providedArgs) throws Exception { Object[] args = getMethodArgumentValues(request, mavContainer, providedArgs); if (logger.isTraceEnabled()) { StringBuilder sb = new StringBuilder("Invoking ["); sb.append(getBeanType().getSimpleName()).append("."); sb.append(getMethod().getName()).append("] method with arguments "); sb.append(Arrays.asList(args)); logger.trace(sb.toString()); } Object returnValue = doInvoke(args); if (logger.isTraceEnabled()) { logger.trace("Method [" + getMethod().getName() + "] returned [" + returnValue + "]"); } return returnValue; }
/** * Invoke the handler method with the given argument values. */ protected Object doInvoke(Object... args) throws Exception { ReflectionUtils.makeAccessible(getBridgedMethod()); try { return getBridgedMethod().invoke(getBean(), args); } catch (IllegalArgumentException ex) { assertTargetBean(getBridgedMethod(), getBean(), args); String message = (ex.getMessage() != null ? ex.getMessage() : "Illegal argument"); throw new IllegalStateException(getInvocationErrorMessage(message, args), ex); } catch (InvocationTargetException ex) { // Unwrap for HandlerExceptionResolvers ... Throwable targetException = ex.getTargetException(); if (targetException instanceof RuntimeException) { throw (RuntimeException) targetException; } else if (targetException instanceof Error) { throw (Error) targetException; } else if (targetException instanceof Exception) { throw (Exception) targetException; } else { String msg = getInvocationErrorMessage("Failed to invoke controller method", args); throw new IllegalStateException(msg, targetException); } } }
取到值后，关键是ServletInvocableHandlerMethod的handleReturnValue方法，子类RequestResponseBodyMethodProcessor复写了该方法
public void handleReturnValue(Object returnValue, MethodParameter returnType, ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws IOException, HttpMediaTypeNotAcceptableException, HttpMessageNotWritableException { mavContainer.setRequestHandled(true); // Try even with null return value. ResponseBodyAdvice could get involved. writeWithMessageConverters(returnValue, returnType, webRequest); }
/** * Writes the given return value to the given web request. Delegates to * {@link #writeWithMessageConverters(Object, MethodParameter, ServletServerHttpRequest, ServletServerHttpResponse)} */ protected <T> void writeWithMessageConverters(T value, MethodParameter returnType, NativeWebRequest webRequest) throws IOException, HttpMediaTypeNotAcceptableException, HttpMessageNotWritableException { ServletServerHttpRequest inputMessage = createInputMessage(webRequest); ServletServerHttpResponse outputMessage = createOutputMessage(webRequest); writeWithMessageConverters(value, returnType, inputMessage, outputMessage); }
引发血案的馒头就在这个方法里了
/** * Writes the given return type to the given output message. * @param value the value to write to the output message * @param returnType the type of the value * @param inputMessage the input messages. Used to inspect the {@code Accept} header. * @param outputMessage the output message to write to * @throws IOException thrown in case of I/O errors * @throws HttpMediaTypeNotAcceptableException thrown when the conditions indicated by {@code Accept} header on * the request cannot be met by the message converters */ @SuppressWarnings("unchecked") protected <T> void writeWithMessageConverters(T value, MethodParameter returnType, ServletServerHttpRequest inputMessage, ServletServerHttpResponse outputMessage) throws IOException, HttpMediaTypeNotAcceptableException, HttpMessageNotWritableException { Class<?> valueType = getReturnValueType(value, returnType); Type declaredType = getGenericType(returnType); HttpServletRequest request = inputMessage.getServletRequest(); List<MediaType> requestedMediaTypes = getAcceptableMediaTypes(request); List<MediaType> producibleMediaTypes = getProducibleMediaTypes(request, valueType, declaredType); if (value != null && producibleMediaTypes.isEmpty()) { throw new IllegalArgumentException("No converter found for return value of type: " + valueType); } Set<MediaType> compatibleMediaTypes = new LinkedHashSet<MediaType>(); for (MediaType requestedType : requestedMediaTypes) { for (MediaType producibleType : producibleMediaTypes) { if (requestedType.isCompatibleWith(producibleType)) { compatibleMediaTypes.add(getMostSpecificMediaType(requestedType, producibleType)); } } } if (compatibleMediaTypes.isEmpty()) { if (value != null) { throw new HttpMediaTypeNotAcceptableException(producibleMediaTypes); } return; } List<MediaType> mediaTypes = new ArrayList<MediaType>(compatibleMediaTypes); MediaType.sortBySpecificityAndQuality(mediaTypes); MediaType selectedMediaType = null; for (MediaType mediaType : mediaTypes) { 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<?> messageConverter : this.messageConverters) { if (messageConverter instanceof GenericHttpMessageConverter) { if (((GenericHttpMessageConverter<T>) messageConverter).canWrite( declaredType, valueType, selectedMediaType)) { value = (T) getAdvice().beforeBodyWrite(value, returnType, selectedMediaType, (Class<? extends HttpMessageConverter<?>>) messageConverter.getClass(), inputMessage, outputMessage); if (value != null) { addContentDispositionHeader(inputMessage, outputMessage); ((GenericHttpMessageConverter<T>) messageConverter).write( value, declaredType, selectedMediaType, outputMessage); if (logger.isDebugEnabled()) { logger.debug("Written [" + value + "] as "" + selectedMediaType + "" using [" + messageConverter + "]"); } } return; } } else if (messageConverter.canWrite(valueType, selectedMediaType)) { value = (T) getAdvice().beforeBodyWrite(value, returnType, selectedMediaType, (Class<? extends HttpMessageConverter<?>>) messageConverter.getClass(), inputMessage, outputMessage); if (value != null) { addContentDispositionHeader(inputMessage, outputMessage); ((HttpMessageConverter<T>) messageConverter).write(value, selectedMediaType, outputMessage); if (logger.isDebugEnabled()) { logger.debug("Written [" + value + "] as "" + selectedMediaType + "" using [" + messageConverter + "]"); } } return; } } } if (value != null) { throw new HttpMediaTypeNotAcceptableException(this.allSupportedMediaTypes); } }
关键变量是selectedMediaType，由它决定了Content-Type究竟是啥，中文会不会有乱码。它又是怎么来的呢，接着看代码。看本文的顶端，我们定义的Controller方法返回的String，所以valueType、declaredType都是String，然后看响应的Content-Type都有哪些
/** * Returns the media types that can be produced: * <ul> * <li>The producible media types specified in the request mappings, or * <li>Media types of configured converters that can write the specific return value, or * <li>{@link MediaType#ALL} * </ul> * @since 4.2 */ @SuppressWarnings("unchecked") protected List<MediaType> getProducibleMediaTypes(HttpServletRequest request, Class<?> valueClass, Type declaredType) { Set<MediaType> mediaTypes = (Set<MediaType>) request.getAttribute(HandlerMapping.PRODUCIBLE_MEDIA_TYPES_ATTRIBUTE); if (!CollectionUtils.isEmpty(mediaTypes)) { return new ArrayList<MediaType>(mediaTypes); } else if (!this.allSupportedMediaTypes.isEmpty()) { List<MediaType> result = new ArrayList<MediaType>(); 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); } }
从canWrite方法过滤出StringHttpMessageConverter是支持的转换类，而它的Content-Type就是text/plain;charset=ISO-8859-1，而且它就放在producibleMediaTypes列表的第一个，后面直接就取ISO-8859-1作为字符编码了，中文乱码就来了。
定位到这里，要解决中文乱码也就简单了，我们看上面方法开始标红的代码，其实先是从produces注解开始拿字符编码的，取不到才去转换器里一个个取，所以我们只要在Controller上加个注解produces = "application/json;charset=utf-8"就解决了。