ajax调用后台controller方法时报415 (Unsupported Media Type)错误

spring mvc 下，ajax调用后台controller方法时报415 (Unsupported Media Type)错误

错误：ajax的post方法调用后台controller方法时报错：415 (Unsupported Media Type)。下面是错误时的代码

前端：
var url =“xxx/xxQuery.action”;
var params={
year:‘2017’
}
ajax(url,params,function(result){
console.log(result);

})

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function ajax(url,params,callback,contentType){
var ajaxoptions={
url:url,
data:params,
type:“POST”,
dataType:“json”,
// contentType:",//application/x-www-form-urlencoded application/json"
success:function(res){
callback(res);
},
error:function(){
callback({success:false,description:“失败”}); }
}
if(contentType!=undefined){
ajaxoptions=$.extend(ajaxoptions,{contentType:contentType})
}

   $.ajax(ajaxoptions);

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}
var url =“xxx/xxQuery.action”;
var params={
year:‘2017’
}
ajax(url,params,function(result){
console.log(result);

})

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function ajax(url,params,callback,contentType){
var ajaxoptions={
url:url,
data:params,
type:“POST”,
dataType:“json”,
// contentType:",//application/x-www-form-urlencoded application/json"
success:function(res){
callback(res);
},
error:function(){
callback({success:false,description:“失败”}); }
}
if(contentType!=undefined){
ajaxoptions=$.extend(ajaxoptions,{contentType:contentType})
}

   $.ajax(ajaxoptions);

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}

后台：

复制代码
@RequestMapping(value = { “/xxx/xxQuery.action” })
@ResponseBody
public Map<String, Object> xxQuery(Model model, HttpServletRequest request,
@RequestBody ORParameter parameter) {

    ........
    return result;
}

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复制代码
我的思路：对后台spring mvc不熟，只是有个概念服务器应该接收到了http请求，只是因为某种原因没有进入controller，而提前被拦截处理了。然后就开始找http处理的源头，笨办法,从HttpServlet.service开始找 -> DispatcherServlet.doDispatch,找到关键的处理方法handle

@Override
protected Object readWithMessageConverters(NativeWebRequest webRequest, MethodParameter methodParam,
Type paramType) throws IOException, HttpMediaTypeNotSupportedException {

    HttpServletRequest servletRequest = webRequest.getNativeRequest(HttpServletRequest.class);
    HttpInputMessage inputMessage = new ServletServerHttpRequest(servletRequest);

    RequestBody ann = methodParam.getParameterAnnotation(RequestBody.class);
    if (!ann.required()) { //由于controller调用的这个方法参数加了@RequestBody，ann.required()这个为true就不走这里，

        InputStream inputStream = inputMessage.getBody();
        if (inputStream == null) {
            return null;
        }
        else if (inputStream.markSupported()) {
            inputStream.mark(1);
            if (inputStream.read() == -1) {
                return null;
            }
            inputStream.reset();
        }
        else {
            final PushbackInputStream pushbackInputStream = new PushbackInputStream(inputStream);
            int b = pushbackInputStream.read();
            if (b == -1) {
                return null;
            }
            else {
                pushbackInputStream.unread(b);
            }
            inputMessage = new ServletServerHttpRequest(servletRequest) {
                @Override
                public InputStream getBody() {
                    // Form POST should not get here
                    return pushbackInputStream;
                }
            };
        }
    }

    return super.readWithMessageConverters(inputMessage, methodParam, paramType);
}

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package org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodArgumentResolver(类);
@SuppressWarnings(“unchecked”)
protected Object readWithMessageConverters(HttpInputMessage inputMessage,
MethodParameter methodParam, Type targetType) throws IOException, HttpMediaTypeNotSupportedException {

    MediaType contentType;
    try {
        contentType = inputMessage.getHeaders().getContentType();
    }
    catch (InvalidMediaTypeException ex) {
        throw new HttpMediaTypeNotSupportedException(ex.getMessage());
    }
    if (contentType == null) {
        contentType = MediaType.APPLICATION_OCTET_STREAM;
    }

    Class<?> contextClass = methodParam.getDeclaringClass();
    Map<TypeVariable, Type> map = GenericTypeResolver.getTypeVariableMap(contextClass);
    Class<T> targetClass = (Class<T>) GenericTypeResolver.resolveType(targetType, map);

    for (HttpMessageConverter<?> converter : this.messageConverters) {
        if (converter instanceof GenericHttpMessageConverter) {
            GenericHttpMessageConverter genericConverter = (GenericHttpMessageConverter) converter;
            if (genericConverter.canRead(targetType, contextClass, contentType)) {
                if (logger.isDebugEnabled()) {
                    logger.debug("Reading [" + targetType + "] as \"" +
                            contentType + "\" using [" + converter + "]");
                }
                return genericConverter.read(targetType, contextClass, inputMessage);
            }
        }
        if (targetClass != null) {
            if (converter.canRead(targetClass, contentType)) {
                if (logger.isDebugEnabled()) {
                    logger.debug("Reading [" + targetClass.getName() + "] as \"" +
                            contentType + "\" using [" + converter + "]");
                }
                return ((HttpMessageConverter<T>) converter).read(targetClass, inputMessage);
            }
        }
    }

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//这里是报错位置
throw new HttpMediaTypeNotSupportedException(contentType, this.allSupportedMediaTypes);//没有找到参数对应的转换器就报错
}

原因：@RequestBody

a) 该注解用于读取Request请求的body部分数据，根据request的header部分的Content-Type类型，匹配HttpMessageConverter进行解析，然后把相应的数据绑定到要返回的对象上；

b) 再把HttpMessageConverter返回的对象数据绑定到 controller中方法的参数上。

前台没有注明后台解析参考的content-type，默认为application/x-www-form-urlencoded ，同时参数是对象也是不是json字符串，后台找不到解析方法。

解决：content-type为application/json格式的数据可以被jackson解读(这里在canread判断时用到)，json对应jackson处理请求中的参数，jackson的参数应该是json字符串（enum JsonToken 这里有关于解析的字符串格式token的枚举内容： START_OBJECT("{")…）， 而不是application/x-www-form-urlencoded编码的字符串“year=2017“。

所以前端请求需改为：

    ajax(url,JSON.stringify(params),function(result){
            console.log(result); 
            },"application/json")

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正确解析时，调用的转换器是jackson。

备注：调用到参数解析的调用栈

可参考：https://blog.csdn.net/mingtianhaiyouwo/article/details/51445345

1.浏览器请求时没有设置Content-Type为Json，对于浏览器来说就是要把POST的内容放到jsonData属性中，而不是params。

2.第三方工具没有设置Content-Type的功能，默认的是Content-Type: application/x-www-form-urlencoded

@PostMapping("/run4")
public R<List<Empbole>> run4(@RequestBody BzydFzHonor bzydFzHono) throws Exception {
    String userid = bzydFzHono.getUserid();
    QueryWrapper<Empbole> empboleQueryWrapper = new QueryWrapper<>();
    empboleQueryWrapper.eq("user_id",userid);
    List<Empbole> userList = empboleService.list(empboleQueryWrapper);

    return R.ok(userList);
}

function ajax(url, params, callback, contentType) {
    var ajaxoptions = {
        url: url,
        data: params,
        type: 'POST',
        dataType: 'json',
        success: function (res) {
            callback(res);
        },
        error: function () {
            callback({success: false, description: 'false'});
        }
    }
    if (contentType != undefined) {
        ajaxoptions = $.extend(ajaxoptions, {contentType: contentType})
    }
    $.ajax(ajaxoptions);
}

ajax("http://111.75.222.140:8084/empbole/run4",JSON.stringify(postData),function(result){
    console.log(result);
},"application/json")