spring mvc加了@produces注解后报406

　　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<MediaType>(consumableMediaTypes));
        }
        else if (!producibleMediaTypes.isEmpty()) {
            throw new HttpMediaTypeNotAcceptableException(new ArrayList<MediaType>(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<ProduceMediaTypeExpression> result = new LinkedHashSet<ProduceMediaTypeExpression>(expressions);
        for (Iterator<ProduceMediaTypeExpression> 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<MediaType> acceptedMediaTypes = getAcceptedMediaTypes(request);
            for (MediaType acceptedMediaType : acceptedMediaTypes) {
                if (getMediaType().isCompatibleWith(acceptedMediaType)) {
                    return true;
                }
            }
            return false;
        }

private List<MediaType> getAcceptedMediaTypes(HttpServletRequest request) throws HttpMediaTypeNotAcceptableException {
        List<MediaType> 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 List<MediaType> resolveMediaTypes(NativeWebRequest request)
            throws HttpMediaTypeNotAcceptableException {

        for (ContentNegotiationStrategy strategy : this.strategies) {
            List<MediaType> 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 List<MediaType> resolveMediaTypes(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<MediaType> 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。