org.springframework.web.HttpMediaTypeNotSupportedException: Content type 'multipart/form-data;boundary=----WebKitFormBoundaryRAYPKeHKTYSNdzc1;charset=UTF-8' not supported

使用 FormData Ajax 上传文件，后台使用 Spring boot，报 org.springframework.web.HttpMediaTypeNotSupportedException 错误：

org.springframework.web.HttpMediaTypeNotSupportedException:
    Content type 'multipart/form-data;boundary=----WebKitFormBoundaryRAYPKeHKTYSNdzc1;charset=UTF-8' not supported

ajax 文件上传：

var formData = new FormData();
formData.append('file', file);

$.ajax({
    url: url,
    type: 'post',
    data: formData,
    contentType: false,  
    processData: false, 
    success: function(data) {
        self.onSuccess(data);
        self.deleteFile(file);
    },
    error: function(data) {
        self.onFailure(data);
    }
});

后台 Controller 接口：

@RequestMapping(value = "/upload", method = RequestMethod.POST)
@ResponseBody
public String upload(@RequestParam("file") MultipartFile file, @RequestBody User user) {
    // 业务处理
}

除了后台报错的日志，使用 Postman 测试返回的消息头：

"timestamp": 1536114316870,
"status": 415,
"error": "Unsupported Media Type",
"exception": "org.springframework.web.HttpMediaTypeNotSupportedException",
"message": "Content type 'multipart/form-data;boundary=----WebKitFormBoundaryTVc9eDC2a2elulOx;charset=UTF-8' not supported",
"path": "/upload"