Global Exception Handler

@RestControllerAdvice

@RestControllerAdvice
@Slf4j
public class GlobalExceptionHandler {

    @ExceptionHandler(ResourceNotFoundException.class)
    public ResponseEntity<ErrorResponse> handleNotFound(
            ResourceNotFoundException ex) {
        log.warn("Resource not found: {}", ex.getMessage());
        return ResponseEntity.status(404).body(
            ErrorResponse.of("NOT_FOUND", ex.getMessage()));
    }

    @ExceptionHandler(ValidationException.class)
    public ResponseEntity<ErrorResponse> handleValidation(
            ValidationException ex) {
        log.warn("Validation failed: {}", ex.getMessage());
        return ResponseEntity.status(422).body(
            ErrorResponse.of("VALIDATION_ERROR", ex.getMessage()));
    }

    @ExceptionHandler(BusinessException.class)
    public ResponseEntity<ErrorResponse> handleBusiness(
            BusinessException ex) {
        log.error("Business error: {}", ex.getMessage());
        return ResponseEntity.status(409).body(
            ErrorResponse.of(ex.getCode(), ex.getMessage()));
    }

    @ExceptionHandler(Exception.class)
    public ResponseEntity<ErrorResponse> handleGeneral(Exception ex) {
        log.error("Unexpected error", ex);
        return ResponseEntity.status(500).body(
            ErrorResponse.of("INTERNAL_ERROR",
                "An unexpected error occurred"));
    }
}

Custom Exceptions

@ResponseStatus(HttpStatus.NOT_FOUND)
public class ResourceNotFoundException extends RuntimeException {
    public ResourceNotFoundException(String message) {
        super(message);
    }
}

@ResponseStatus(HttpStatus.CONFLICT)
public class BusinessException extends RuntimeException {
    private final String code;

    public BusinessException(String code, String message) {
        super(message);
        this.code = code;
    }
}

Error Response DTO

@Data
public class ErrorResponse {
    private String code;
    private String message;
    private String traceId;
    private Instant timestamp;

    public static ErrorResponse of(String code, String message) {
        ErrorResponse error = new ErrorResponse();
        error.setCode(code);
        error.setMessage(message);
        error.setTraceId(MDC.get("traceId"));
        error.setTimestamp(Instant.now());
        return error;
    }
}

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 Global 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