spring MVC接收请求体总是多一个等号

spring MVC接收请求体总是多一个等号

比如我发送的请求体是字符串aaa
spring MVC 接收到的是aaa=
接口如下:

/***
     * @param requestInfoBean
     * @return
     */
    @RequestMapping(value = "/ajax", produces = SystemHWUtil.RESPONSE_CONTENTTYPE_JSON_UTF)
    @ResponseBody
    public String ajax(@RequestBody String requestInfoBean,HttpServletRequest request) {
        System.out.println(requestInfoBean);
        System.out.println(request.getHeader("Content-Type"));
                return null;
    }

为什么呢?
因为请求的content type不对
应该是:application/json;charset=UTF-8
而我设置的content type是:
application/x-www-form-urlencoded;charset=UTF-8