How can applications on Spring inform users about errors that occur?

In Spring applications, there are several approaches often used to inform the user about errors:

1. Exception handling with @ExceptionHandler — in controllers or globally via @ControllerAdvice, you can intercept exceptions and return understandable error messages.

2. Using BindingResult during form validation — after data validation, errors can be obtained and passed to the View for user display.

3. Returning ResponseEntity with errors in REST API — in case of errors, an object describing the problem and the corresponding HTTP status is formed.

4. Flash Attributes in web applications — for passing error messages between requests.

Example of exception handling with @ControllerAdvice:

@ControllerAdvice
public class GlobalExceptionHandler {
    @ExceptionHandler(EntityNotFoundException.class)
    public ResponseEntity<String> handleNotFound(EntityNotFoundException ex) {
        return ResponseEntity.status(HttpStatus.NOT_FOUND).body("Error: " + ex.getMessage());
    }
}

Thus, the user receives an informative error message adapted to the application context.