问题背景：调用http的post接口返回一个String类型的字符串时中文出现乱码，定位出问题后在@RequestMapping里加produces注解produces = "application/json;charset=utf-8"，再次请求http报406，代码发现spring抛出异常：org.springframework.web.HttpMediaTypeNotAcceptableException: Could not find acceptable representation。
问题代码附上：
/** * 执行登陆行为 * * @author wulinfeng * @param request * @param user * @return * @throws ServletException * @throws IOException */ @RequestMapping(value = "/loginAction.html", method = RequestMethod.POST, produces = "application/json;charset=utf-8") public @ResponseBody String loginAction(HttpServletRequest request, HttpServletResponse response, @RequestBody UserBean user) throws ServletException, IOException { // 验证码校验 String validateCode = (String)request.getSession().getAttribute("randomString"); if (StringUtils.isEmpty(validateCode) || !validateCode.equals(user.getValidate().toUpperCase())) { return PropertiesConfigUtil.getProperty("verify_code_error"); } // 用户名密码校验 String result = testPillingService.login(user.getUsername(), user.getPassword()); // 校验通过，创建token并放入session中；校验失败，返回错误描述 if ("success".equals(result)) { String tokenId = UUID.randomUUID().toString(); // 登陆成功后是使用cookie还是session来存放tokenId if (IS_COOKIE.equals("1")) { Cookie cookie = new Cookie("tokenId", tokenId); cookie.setMaxAge(3 * 24 * 60 * 60); // 3天过期 response.addCookie(cookie); } else { request.getSession(true).setAttribute("tokenId", tokenId); } if (user.getUsername().toUpperCase().equals("ADMIN")) { return "register"; } } return result; } 问题定位：spring源码逆向跟踪，我们从异常抛出的地方回溯到问题发生的地方。
异常所在地：RequestMappingInfoHandlerMapping类235行，标红；producibleMediaTypes实例化处，218行，标红
if (patternAndMethodMatches.isEmpty()) { consumableMediaTypes = getConsumableMediaTypes(request, patternMatches); producibleMediaTypes = getProducibleMediaTypes(request, patternMatches); paramConditions = getRequestParams(request, patternMatches); } else { consumableMediaTypes = getConsumableMediaTypes(request, patternAndMethodMatches); producibleMediaTypes = getProducibleMediaTypes(request, patternAndMethodMatches); paramConditions = getRequestParams(request, patternAndMethodMatches); } if (!consumableMediaTypes.isEmpty()) { MediaType contentType = null; if (StringUtils.hasLength(request.getContentType())) { try { contentType = MediaType.parseMediaType(request.getContentType()); } catch (InvalidMediaTypeException ex) { throw new HttpMediaTypeNotSupportedException(ex.getMessage()); } } throw new HttpMediaTypeNotSupportedException(contentType, new ArrayList (consumableMediaTypes)); } else if (!producibleMediaTypes.isEmpty()) { throw new HttpMediaTypeNotAcceptableException(new ArrayList (producibleMediaTypes)); } else if (!CollectionUtils.isEmpty(paramConditions)) { throw new UnsatisfiedServletRequestParameterException(paramConditions, request.getParameterMap()); } else { return null; } 判断请求是否能匹配注解produces配置的Content-Type（即“application/json;charset=utf-8”）：类258行
private Set<MediaType> getProducibleMediaTypes(HttpServletRequest request, Set<RequestMappingInfo> partialMatches) { Set<MediaType> result = new HashSet<MediaType>(); for (RequestMappingInfo partialMatch : partialMatches) { if (partialMatch.getProducesCondition().getMatchingCondition(request) == null) { result.addAll(partialMatch.getProducesCondition().getProducibleMediaTypes()); } } return result; }
匹配逻辑：ProducesRequestCondition类185行
public ProducesRequestCondition getMatchingCondition(HttpServletRequest request) { if (isEmpty()) { return this; } Set result = new LinkedHashSet (expressions); for (Iterator iterator = result.iterator(); iterator.hasNext();) { ProduceMediaTypeExpression expression = iterator.next(); if (!expression.match(request)) { iterator.remove(); } } return (result.isEmpty()) ? null : new ProducesRequestCondition(result, this.contentNegotiationManager); } 匹配请求的Content-Type：AbstractMediaTypeExpression类75行
public final boolean match(HttpServletRequest request) { try { boolean match = matchMediaType(request); return (!this.isNegated ? match : !match); } catch (HttpMediaTypeException ex) { return false; } } 获取请求匹配的Content-Type：ProducesRequestCondition类300行、236行
protected boolean matchMediaType(HttpServletRequest request) throws HttpMediaTypeNotAcceptableException { List acceptedMediaTypes = getAcceptedMediaTypes(request); for (MediaType acceptedMediaType : acceptedMediaTypes) { if (getMediaType().isCompatibleWith(acceptedMediaType)) { return true; } } return false; } private ListgetAcceptedMediaTypes(HttpServletRequest request) throws HttpMediaTypeNotAcceptableException { List mediaTypes = this.contentNegotiationManager.resolveMediaTypes(new ServletWebRequest(request)); return mediaTypes.isEmpty() ? Collections.singletonList(MediaType.ALL) : mediaTypes; }
解析请求Content-Type：ContentNegotiationManager类109行
public ListresolveMediaTypes(NativeWebRequest request) throws HttpMediaTypeNotAcceptableException { for (ContentNegotiationStrategy strategy : this.strategies) { List mediaTypes = strategy.resolveMediaTypes(request); if (mediaTypes.isEmpty() || mediaTypes.equals(MEDIA_TYPE_ALL)) { continue; } return mediaTypes; } return Collections.emptyList(); }
好了，到底了，最终解析Content-Type的地方在这里，AbstractMappingContentNegotiationStrategy类
public ListresolveMediaTypes(NativeWebRequest webRequest) throws HttpMediaTypeNotAcceptableException { return resolveMediaTypeKey(webRequest, getMediaTypeKey(webRequest)); } /** * An alternative to { @link #resolveMediaTypes(NativeWebRequest)} that accepts * an already extracted key. * @since 3.2.16 */ public List resolveMediaTypeKey(NativeWebRequest webRequest, String key) throws HttpMediaTypeNotAcceptableException { if (StringUtils.hasText(key)) { MediaType mediaType = lookupMediaType(key); if (mediaType != null) { handleMatch(key, mediaType); return Collections.singletonList(mediaType); } mediaType = handleNoMatch(webRequest, key); if (mediaType != null) { addMapping(key, mediaType); return Collections.singletonList(mediaType); } } return Collections.emptyList(); }
怎么取到html这个后缀的呢？AbstractMappingContentNegotiationStrategy的子类PathExtensionContentNegotiationStrategy类114行
protected String getMediaTypeKey(NativeWebRequest webRequest) { HttpServletRequest request = webRequest.getNativeRequest(HttpServletRequest.class); if (request == null) { logger.warn("An HttpServletRequest is required to determine the media type key"); return null; } String path = this.urlPathHelper.getLookupPathForRequest(request); String filename = WebUtils.extractFullFilenameFromUrlPath(path); String extension = StringUtils.getFilenameExtension(filename); return (StringUtils.hasText(extension)) ? extension.toLowerCase(Locale.ENGLISH) : null; }
回到最顶端，我的@RequestMapping匹配的url是“/loginAction.html”，getMediaTypeKey方法就是在取url后缀，拿到html后作为上面resolveMediaTypeKey方法的里key，然后去调用lookupMediaType方法
protected MediaType lookupMediaType(String extension) { return this.mediaTypes.get(extension.toLowerCase(Locale.ENGLISH)); } 而这里mediaTypes对象是什么东西呢？它是启动时加载的，我这里取出来是这样子的：{xml=application/xml, html=text/html, json=application/json}，所以最终解析出来我的请求竟然是text/html，而实际上我从ajax调用http时是设置了Content-Type为application/json;charset=UTF-8的。
看到这里，问题已经出来了，url以html结尾，导致请求头设置的Content-Type被覆盖了。那么解决方式相对就简单了，不以html结尾即可，我这里是直接把/loginAction.html改为/loginAction，重新试一下，406没有了，中文也出来了。