Exception Handling in REST

@RestController
public class UserController {
    
    @GetMapping("/users/{id}")
    public User getUser(@PathVariable int id) {
        return userService.findById(id)
                .orElseThrow(() -> new UserNotFoundException("User not found with id: " + id));
    }
    
    @ExceptionHandler(UserNotFoundException.class)
    @ResponseStatus(HttpStatus.NOT_FOUND)
    public ErrorResponse handleUserNotFound(UserNotFoundException ex) {
        return new ErrorResponse("USER_NOT_FOUND", ex.getMessage());
    }
}

@ControllerAdvice
public class GlobalExceptionHandler {
    
    // Handle specific exceptions
    @ExceptionHandler(UserNotFoundException.class)
    @ResponseStatus(HttpStatus.NOT_FOUND)
    public ErrorResponse handleUserNotFound(UserNotFoundException ex) {
        return new ErrorResponse(
            "USER_NOT_FOUND",
            ex.getMessage(),
            LocalDateTime.now()
        );
    }
    
    // Handle validation errors
    @ExceptionHandler(MethodArgumentNotValidException.class)
    @ResponseStatus(HttpStatus.BAD_REQUEST)
    public ErrorResponse handleValidationExceptions(MethodArgumentNotValidException ex) {
        Map errors = new HashMap<>();
        ex.getBindingResult().getAllErrors().forEach((error) -> {
            String fieldName = ((FieldError) error).getField();
            String errorMessage = error.getDefaultMessage();
            errors.put(fieldName, errorMessage);
        });
        return new ErrorResponse("VALIDATION_FAILED", errors.toString());
    }
    
    // Handle all other exceptions (fallback)
    @ExceptionHandler(Exception.class)
    @ResponseStatus(HttpStatus.INTERNAL_SERVER_ERROR)
    public ErrorResponse handleGenericException(Exception ex) {
        return new ErrorResponse(
            "INTERNAL_ERROR",
            "An unexpected error occurred"
        );
    }
}

public class ErrorResponse {
    private String errorCode;
    private String message;
    private LocalDateTime timestamp;
    
    // constructors, getters, setters
}

@ExceptionHandler(UserNotFoundException.class)
public ResponseEntity handleUserNotFound(UserNotFoundException ex) {
    ErrorResponse error = new ErrorResponse(
        "USER_NOT_FOUND",
        ex.getMessage(),
        LocalDateTime.now()
    );
    return new ResponseEntity<>(error, HttpStatus.NOT_FOUND);
}

• Always return meaningful error responses, not stack traces.
• Use @ExceptionHandler in controllers for local handling.
• Use @ControllerAdvice for global exception handling across all controllers.
• Create a consistent ErrorResponse class for all errors.
• Use ResponseEntity for full control over response status and headers.