why is Spring Boot returning a string instead of JSON

Question

According to this question, my method should be sending a JSON object via Jackson:

Returning JSON object as response in Spring Boot

But I am receiving a string at the client.

Here's the relevant parts:

@CrossOrigin(origins = "*")
@RestController
public class AuthController {

 @PostMapping("/api/signup")
    public String signup(HttpServletRequest request, HttpServletResponse response){
      return "{'status':'fail', 'message':'foo'}";
    }
}

Answer 1

You explicitly say return "some string"; so it does what you asked for.

Instead, you should construct an object. I would define the following class and enum:

public class SignupDto {
    private Status status;
    private String message;

    public SignupDto() {
    }

    public SignupDto(Status status, String message) {
        this.status = status;
        this.message = message;
    }

    public Status getStatus() {
        return status;
    }

    public void setStatus(Status status) {
        this.status = status;
    }

    public String getMessage() {
        return message;
    }

    public void setMessage(String message) {
        this.message = message;
    }

    public enum Status {
        FAIL,
        SUCCESS
    }        
}

And use it as following:

public SignupDto signup(HttpServletRequest request, HttpServletResponse response) {
  return new SignupDto(SignupDto.Status.FAIL, "foo");
}

Jackson will do the serialising automatically.

Answer 2

While you were right about single quotes, you can achieve the JSON response without using DTO if you don't want to. You can try this:

@PostMapping("/api/signup")
public ResponseEntity signup(HttpServletRequest request, HttpServletResponse response) {
    return ResponseEntity
            .status(<http_status>)
            .contentType(MediaType.APPLICATION_JSON)
            .body("{\"status\":\"fail\", \"message\":\"foo\"}");
}