Exception Handling in Spring

@ExceptionHandler

@RestController
public class ProductController {

    @GetMapping("/{id}")
    public ResponseEntity<Product> getProduct(@PathVariable Long id) {
        Product product = productService.findById(id)
            .orElseThrow(() -> new ResourceNotFoundException(
                "Product not found with id: " + id));
        return ResponseEntity.ok(product);
    }

    @ExceptionHandler(ResourceNotFoundException.class)
    public ResponseEntity<ErrorResponse> handleNotFound(
            ResourceNotFoundException ex) {
        return ResponseEntity.status(404).body(
            new ErrorResponse("NOT_FOUND", ex.getMessage()));
    }

    @ExceptionHandler(MethodArgumentNotValidException.class)
    public ResponseEntity<ErrorResponse> handleValidation(
            MethodArgumentNotValidException ex) {
        String message = ex.getBindingResult().getFieldErrors().stream()
            .map(e -> e.getField() + ": " + e.getDefaultMessage())
            .collect(Collectors.joining(", "));
        return ResponseEntity.status(422).body(
            new ErrorResponse("VALIDATION_ERROR", message));
    }
}

Exception Response Format

{
  "code": "RESOURCE_NOT_FOUND",
  "message": "Product not found with id: 123",
  "timestamp": "2025-01-15T10:30:00Z"
}

Custom Exceptions

public class NotFoundException extends RuntimeException {
    public NotFoundException(String message) {
        super(message);
    }
}

Handling

• Catch specific exceptions
• Handle at appropriate layer
• Log with context
• Return meaningful errors

Best Practices

• Use unchecked exceptions for bugs
• Use checked exceptions for recoverable
• Don't catch and ignore
• Include correlation IDs

Key Points

• Understanding Exception Handling is essential for production systems
• Always consider scalability and maintainability
• Test thoroughly before deploying to production
• Monitor performance and set up alerting

Common Patterns

1. Validation: Always validate input at the boundary
2. Error Handling: Use structured error responses
3. Logging: Log key events for debugging
4. Testing: Unit, integration, and load tests
5. Documentation: Keep docs updated with code changes