Exception Handling in RESTful Spring Boot Services

Question

So I have various API endpoints defined in my Spring Boot services that throws various custom exceptions. But I am not able to make a distinction between Checked and Unchecked exceptions.

So should my custom exception be Checked or Unchecked exception?

Examples:

1. UserNotFoundException
2. EmailAlreadyExistsException
3. JWTTokenMalformedException
4. DatabaseNodeFailureException

These exceptions are parsed by Spring ControllerAdvice, converted to ResponseEntity and sent to client.

How would you define above custom created exceptions as Checked or Unchecked? Also let me know if there is any thumb rule to decide if your exception should be Checked or Unchecked?

Answer 1

You are good even if you have all your exceptions as RuntimeException since you delegate error response generation to ControllerAdvice. Regardless of whether it is a RESTful Spring Boot Service or just another Java Application the premise to throw Checked or Unchecked Exceptions from a method largely remains on whether the caller MUST (Checked) or SHALL (Runtime) handle exception.

For example when calling

FileInputStream fis = new FileInputStream("somefile.txt");

The constructor FileInputStream(String fileName) forces to handle the File not found exceptional scenario. Thus it throws a FileNotFoundException which is a checked exception and MUST be handled by the caller at the calling location itself.

Answer 2

try defining all of them as unchecked and define a method for each type of exception where you need specific handling with @ExceptionHandler in ControllerAdvice

@ExceptionHandler(value = { EmailAlreadyExistsException.class, UserAlreadyExistsException.class })
protected ResponseEntity<Object> handleAlreadyExistsException(RuntimeException ex, WebRequest request) {
    String yourErrMsg = "Some error desc.."
    List<String> errorMessages = List.of(yourErrMsg);
    HttpStatus httpStatusForTheError = HttpStatus.BAD_REQUEST;
    return new ResponseEntity<List<String>>
(errorMessages, httpStatusForTheError);
}

and one final method as a catch all

@ExceptionHandler(value = RuntimeException.class)
protected ResponseEntity<Object> handle EmailAlreadyExistsException(RuntimeException ex, WebRequest request) {
    
    String yourErrMsg = "We are sorry, something went wrong."//don't disclose the stacktrace
    List<String> errorMessages = List.of(yourErrMsg);
    
    return new ResponseEntity<List<String>>
(errorMessages, HttpStatus.INTERNAL_SERVER_ERROR);
}

example from: https://www.baeldung.com/exception-handling-for-rest-with-spring

Answer 3

Also let me know if there is any thumb rule to decide if your exception should be Checked or Unchecked?

Checked Exception the compiler check and force you to handle the exception

Unchecked Exception the compiler does not warn you and you handle the exception by yourself

The rule you can adopt is the following

• if you are in a dependency case, where for instance you have to handle business rules throught many layers, then use Checked Exception. It will force you to handle your exception in top layers (service > controller)
• if you can't have the control on certain aspect of you application or architecture, such as access to a server or a file available in a location

Read this for more details.