Handling Exceptions in RESTful User Responses

@RestController
@RequestMapping("/api/books")
public class BookController {

    @Autowired
    private BookService bookService;

    // Method to retrieve a book by its ID
    @GetMapping("/{id}")
    public ResponseEntity<Book> getBookById(@PathVariable Long id) {
        Book book = bookService.findBookById(id)
                .orElseThrow(() -> new BookNotFoundException("Book with ID: " + id + " not found."));
        return new ResponseEntity<>(book, HttpStatus.OK);
    }

    // Exception handler for BookNotFoundException
    @ExceptionHandler(BookNotFoundException.class)
    @ResponseStatus(HttpStatus.NOT_FOUND)
    public ResponseEntity<String> handleBookNotFoundException(BookNotFoundException ex) {
        // Log the exception details for debugging
        Logger.log(ex.getMessage());

        // Return a user-friendly message and the appropriate HTTP status
        return ResponseEntity
                .status(HttpStatus.NOT_FOUND)
                .body("Book not found. Please check the provided book ID.");
    }

    // ... other methods or exception handlers ...
}

Explanation:

In the code snippet above, the BookController class includes:

1. Method getBookById:

   • It uses the bookService to attempt to find the book. If the book is not found, bookService.findBookById(id) will return an empty Optional, and the orElseThrow method will throw a BookNotFoundException.

   • The exception message includes the ID of the book that was not found, providing clarity in the logs and to the API users.

2. Exception Handler handleBookNotFoundException:

   • This method remains the same as before. It handles the BookNotFoundException by logging the exception details and returning a user-friendly message along with a 404 Not Found status.

By including the getBookById method, we demonstrate a typical scenario in a RESTful service where a requested resource (in this case, a book) might not exist, leading to an exception that is gracefully handled by the handleBookNotFoundException method.

---

This structure ensures that your REST API for book management not only handles requests but also deals with exceptions in a user-friendly manner, improving the reliability and usability of your service.