spring boot backend FASTJSON, error code 415, 500

$.post({
    url: "/register",
    dataType: "json",
    contentType: "application/json",
    data: JSON.stringify(info),
    success: function (data) {

    }
});

It must contain:

dataType: "JSON",            
contentType: "file application / JSON", 415 without an error occurs rear 

spring boot code is as follows

@PostMapping("/register")
    @ResponseBody
    public String register(@RequestBody JSONObject info) {
        return null；  
   }

Otherwise, you must add @RequestBody 500 errors