spring mvc 下，ajax調用后台controller方法時報415 (Unsupported Media Type)錯誤

 

錯誤：ajax的post方法調用后台controller方法時報錯：415 (Unsupported Media Type)。下面是錯誤時的代碼

前端：

var url ="xxx/xxQuery.action";
var params={
			year:'2017'
		}				    					    	
	ajax(url,params,function(result){
			console.log(result);	
		
	})


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:"失敗"});	         		 }
	   }
	if(contentType!=undefined){
	   			 ajaxoptions=$.extend(ajaxoptions,{contentType:contentType})
	   }
	   		 
	   $.ajax(ajaxoptions);
}

　　

后台：

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

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

我的思路：對后台spring mvc不熟，只是有個概念服務器應該接收到了http請求，只是因為某種原因沒有進入controller，而提前被攔截處理了。然后就開始找http處理的源頭，笨辦法,從HttpServlet.service開始找 -> DispatcherServlet.doDispatch,找到關鍵的處理方法handle

拋出錯誤的位置

package org.springframework.web.servlet.mvc.method.annotation. RequestResponseBodyMethodProcessor;

@Override
	protected <T> 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()) { //由於controller調用的這個方法參數加了@RequestBody，ann.required()這個為true就不走這里，

			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);
	}

package org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodArgumentResolver(類);


@SuppressWarnings("unchecked")
	protected <T> 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);
				}
			}
		}
　　　　　　　　　　//這里是報錯位置
		throw new HttpMediaTypeNotSupportedException(contentType, this.allSupportedMediaTypes);//沒有找到參數對應的轉換器就報錯
	}

　　

 原因：@RequestBody

  　a) 該注解用於讀取Request請求的body部分數據，根據request的header部分的Content-Type類型，匹配HttpMessageConverter進行解析，然后把相應的數據綁定到要返回的對象上；

　　b) 再把HttpMessageConverter返回的對象數據綁定到 controller中方法的參數上。

　　前台沒有注明后台解析參考的content-type，默認為application/x-www-form-urlencoded ，同時參數是對象也是不是json字符串，后台找不到解析方法。

解決：content-type為application/json格式的數據可以被jackson解讀(這里在canread判斷時用到)，json對應jackson處理請求中的參數，jackson的參數應該是json字符串（enum JsonToken 這里有關於解析的字符串格式token的枚舉內容： START_OBJECT("{").....）， 而不是application/x-www-form-urlencoded編碼的字符串“year=2017“。

所以前端請求需改為： 

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

 

　　

正確解析時，調用的轉換器是jackson。

 

備注：調用到參數解析的調用棧

 

可參考：https://blog.csdn.net/mingtianhaiyouwo/article/details/51445345

1.瀏覽器請求時沒有設置Content-Type為Json，對於瀏覽器來說就是要把POST的內容放到jsonData屬性中，而不是params。

2.第三方工具沒有設置Content-Type的功能，默認的是Content-Type: application/x-www-form-urlencoded