I tried with your code with a sample spring boot project and I get the error,

No converter for [class org.json.JSONObject]

The reason for this error is explained clearly here. To reiterate the answer, JSONObject classes don't have getters and hence the error. By default spring-boot starter web dependency has Jackson web support which can convert any POJO class to JSON object. So as the answer by @süleyman-can using a POJO is the right way to handle this.

In case, you can't use a POJO class because the fields in the response will be different for each request. For example, you have to send

{"a": "b"}

for one response and

{"c": "d"}

for another response, you can always use Map<String, String> like this,

@RequestMapping(value = "/test", method = RequestMethod.GET)
@ResponseBody
public Map<String, String> test() {
  Map<String, String> test = new HashMap<>();
  test.put("name","caroline");
  return test;
}

and the response would come like this,

{"name":"caroline"}