Spring Boot: How to handle 400 error caused by #RequestParam? - spring-boot

Question

public String(#RequestParam Integer id) {
// ...
}
If id parameter cannot be found in the current request, I will get 400 status code with empty response body. Now I want to return JSON string for this error, how can I make it?
PS: I don't want to use #RequestParam(required = false)

Answer 1

try to use #PathVariable, hope it will meets your requirement.
#RequestMapping(value = "/user/{id}", method = RequestMethod.GET, produces = MediaType.APPLICATION_JSON_VALUE)
public ResponseEntity<User> getUser(#PathVariable("id") long id) {
System.out.println("Fetching User with id " + id);
User user = userService.findById(id);
if (user == null) {
System.out.println("User with id " + id + " not found");
return new ResponseEntity<User>(HttpStatus.NOT_FOUND);
}
return new ResponseEntity<User>(user, HttpStatus.OK);
}

Answer 2

I've made it.
Just override handleMissingServletRequestParameter() method in your own ResponseEntityExceptionHandler class.
#Override
protected ResponseEntity<Object> handleMissingServletRequestParameter(MissingServletRequestParameterException ex, HttpHeaders headers, HttpStatus status, WebRequest request) {
log.warn("miss Request Param");
return new ResponseEntity<>(new FoxResponse(ErrorCode.ARG_INVALID), status);
}

Answer 3

Just had the same problem, but exception thrown is MethodArgumentTypeMismatchException. With #ControllerAdvice error handler all data about #RequestParam error can be retrieved. Here is complete class that worked for me
#ControllerAdvice
#RequestMapping(produces = MediaType.APPLICATION_JSON_VALUE)
public class ControllerExceptionHandler {
#ExceptionHandler(value = {MethodArgumentTypeMismatchException.class})
#ResponseStatus(value = HttpStatus.BAD_REQUEST)
#ResponseBody
public Map<String, String> handleServiceCallException(MethodArgumentTypeMismatchException e) {
Map<String, String> errMessages = new HashMap<>();
errMessages.put("error", "MethodArgumentTypeMismatchException");
errMessages.put("message", e.getMessage());
errMessages.put("parameter", e.getName());
errMessages.put("errorCode", e.getErrorCode());
return errMessages;
}
}