Spring Boot Rest Controller how to return different HTTP status codes?

One of the way to do this is you can use ResponseEntity as a return object.

@RequestMapping(value="/rawdata/", method = RequestMethod.PUT)
public ResponseEntity<?> create(@RequestBody String data) {
    if(everything_fine) {
        return new ResponseEntity<>(RestModel, HttpStatus.OK);
    } else {
        return new ResponseEntity<>(null, HttpStatus.INTERNAL_SERVER_ERROR);
    }
}

A nice way is to use Spring's ResponseStatusException

Rather than returning a ResponseEntityor similar you simply throw the ResponseStatusException from the controller with an HttpStatus and cause, for example:

throw new ResponseStatusException(HttpStatus.BAD_REQUEST, "Cause description here");

This results in a response to the client containing the HTTP status:

{
  "timestamp": "2020-07-09T04:43:04.695+0000",
  "status": 400,
  "error": "Bad Request",
  "message": "Cause description here",
  "path": "/test-api/v1/search"
}

Note: HttpStatus provides many different status codes for your convenience.

There are several options you can use. Quite good way is to use exceptions and class for handling called @ControllerAdvice:

@ControllerAdvice
class GlobalControllerExceptionHandler {
    @ResponseStatus(HttpStatus.CONFLICT)  // 409
    @ExceptionHandler(DataIntegrityViolationException.class)
    public void handleConflict() {
        // Nothing to do
    }
}

Also you can pass HttpServletResponse to controller method and just set response code:

public RestModel create(@RequestBody String data, HttpServletResponse response) {
    // response committed...
    response.setStatus(HttpServletResponse.SC_ACCEPTED);
}

Please refer to the this great blog post for details: Exception Handling in Spring MVC

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NOTE

In Spring MVC using @ResponseBody annotation is redundant - it's already included in @RestController annotation.