How to handle null return value in spring boot

Question

I have a question about spring boot. When I want to get the specific user from my database everything is ok but how can I handle the null response (There is no such a user)? I want to handle the return value of null as ResponseEntity but when there is a user with that id I need to return User details. So I could not set return value as ResponseEntity. Here is the screenshot of the problem:

Here is the code:

@GetMapping("get/{id}") public User findById(@PathVariable int id) throws Exception { try { if(userMapper.findById(id) != null) { return userMapper.findById(id); }else { throw new Exception("YOK ULAN YOK"); } }catch (Exception e) { // TODO: Make perfect return new User(-1); } }

and here is the return value:

{ "email": null, "username": null, "password": null, "name": null, "surname": null, "age": 0, "photoLink": null, "dateOfBirth": null, "phoneNumber": null, "city": null, "country": null, "friendList": null, "plan": null, "id": -1, "planned": false

}

I don't want to send a -1 user, I want to send a user not found response. How can I handle it?

Thanks,

Andrey B. Panfilov · Accepted Answer · 2022-08-20 02:43:02Z

the best way is to change method return type from User to ResponseEntity<?>, smth. like:

@GetMapping("get/{id}") public ResponseEntity<?> findById(@PathVariable int id) throws Exception { User user = userMapper.findById(id); if (user == null) { return ResponseEntity.notFound().build(); } return ResponseEntity.ok(user); }

or using optional:

@GetMapping("get/{id}") public ResponseEntity<?> findById(@PathVariable int id) throws Exception { return Optional.ofNullable(userMapper.findById(id)) .map(ResponseEntity::ok) .orElseGet(ResponseEntity.notFound()::build); }

FrozenBanana · Accepted Answer · 2022-08-20 22:57:38Z

You could use an exception handler to handle these kind of exceptions. To make this work, you could first return an Optional<User> instead of a User. Then you could write your controller as following.

@GetMapping(value = "/get/{id}", produces = MediaType.APPLICATION_JSON_VALUE) public ResponseEntity<User> findById(@PathVariable int id) { return ResponseEntity .status(HttpStatus.OK) .body(userMapper.findById(id) .orElseThrow(UserNotFoundException::new); }

The UserNotFoundException is a custom class. You can extend from RuntimeException so the exception becomes unchecked.

public class UserNotFoundException extends RuntimeException {}

Then you could make an ErrorResponse class. You're free to add the fields you like, but it could look like this:

@Getter @Setter public class ErrorResponse { private int code; private String description; }

You could then handle this UserNotFoundException in an ExceptionHandler:

@RestControllerAdvice @Slf4j public class ApplicationNameExceptionHandler { @ExceptionHandler public ResponseEntity<ErrorResponse> handleException(UserNotFoundException e) { log.info("User not found"); ErrorResponse errorResponse = new ErrorResponse(); errorResponse.setCode(HttpStatus.NOT_FOUND.value()); errorResponse.setDescription("User not found"); return ResponseEntity .status(HttpStatus.NOT_FOUND) .contentType(MediaType.APPLICATION_PROBLEM_JSON) .body(errorResponse); }

The advantage of this approach is that you can keep your controllers concise and tidy and all your controller exceptions can be handled in the same class (ApplicationNameExceptionHandler).

shanfeng · Accepted Answer · 2022-08-20 02:53:43Z

We can try to define a exception with reponse status.

@ResponseStatus(value = HttpStatus.NOT_FOUND) public class ResourceNotFoundException extends RuntimeException { }

And then, in your controller, throw this exception

throw new ResourceNotFoundException()

Or, just set the status of Response directly.
BTW, a better approach is to define our business code to implement it.

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