How to throw an exception back in JSON in Spring Boot

Question

I have a Request Mapping -

  @RequestMapping(\"/fetchErrorMessages\")
  public @ResponseBody int fetchErrorMessages(@RequestParam(\"startTime\") String star         


        

Answer 1

Spring provides a few ways to do this, some more sensible than others depending on your situation.

(Great tutorial here on several options. https://www.baeldung.com/spring-exceptions-json)

My favorite is this one because I want to send back a proper error message and an appropriate http response without creating a superclass or creating helper methods in a utility class or copying boilerplate everywhere.

If you want to inform the caller that the event caused an error (and in proper JSON), use Spring's ResponseStatusException. It gives you access to the httpReponse object so you can also send back a response other than 'ok'.

It wants an exception as one of it's parameters. For one of my scenarios I wanted to inform the caller that they were trying to register a user that already existed. Typically, looking up a user isn't supposed to throw an exception but in this case I created my own exception and I throw it back to the caller in a ResponseStatusException like so:

  @PostMapping("/register")
  public ResponseEntity register(@RequestBody AccountUserDto user) {
    UserDetails userExists = userDetailsService.loadUserByEmail(user.getEmail());

  if (userExists != null) {
      UserExistsException exc = new UserExistsException("Error: Email address " + user.getEmail() +  " is already in use.");
        throw new ResponseStatusException(
        HttpStatus.BAD_REQUEST, "User Exists", exc);
  }
....(fall through and create user)