09_global_exceptions.md

🌍 Global Exception Handling in Spring Boot

📌 Overview

Global exception handling provides a centralized way to manage exceptions across your entire Spring Boot application.

🏗 Key Components

• @ControllerAdvice: Annotation for global exception handling
• @ExceptionHandler: Method-level annotation for specific exceptions
• ResponseEntity: For custom HTTP responses

🛠 Basic Implementation

@ControllerAdvice
public class GlobalExceptionHandler {

    @ExceptionHandler(ResourceNotFoundException.class)
    public ResponseEntity<ErrorResponse> handleResourceNotFound(
        ResourceNotFoundException ex) {
        
        ErrorResponse error = new ErrorResponse(
            "NOT_FOUND",
            ex.getMessage(),
            HttpStatus.NOT_FOUND.value());
            
        return new ResponseEntity<>(error, HttpStatus.NOT_FOUND);
    }
}

📝 Error Response Class

public class ErrorResponse {
private String code;
private String message;
private int status;

    // Constructor, getters and setters
}

🎯 Handling Multiple Exceptions

Option 1: Separate Methods

@ExceptionHandler(MethodArgumentNotValidException.class)
public ResponseEntity<ErrorResponse> handleValidationErrors(
MethodArgumentNotValidException ex) {
// Handle validation errors
}

@ExceptionHandler(AccessDeniedException.class)
public ResponseEntity<ErrorResponse> handleAccessDenied(
AccessDeniedException ex) {
// Handle access denied
}

Option 2: Single Method with Parent Exception

@ExceptionHandler({Exception.class, RuntimeException.class})
public ResponseEntity<ErrorResponse> handleGenericExceptions(
Exception ex) {
// Handle generic exceptions
}

🔍 Best Practices

1. Organize by Exception Type:

   • Create separate @ControllerAdvice classes for different exception categories

2. Standardize Responses:

   • Use consistent error response structures

3. Log Exceptions:

   • Always log exceptions before handling

4. Handle Spring Specific Exceptions:

   • MethodArgumentNotValidException
   • HttpRequestMethodNotSupportedException
   • HttpMediaTypeNotSupportedException

5. Security Considerations:

   • Don't expose sensitive information in error responses

🏹 Custom Business Exceptions

public class BusinessException extends RuntimeException {
private String errorCode;

    public BusinessException(String message, String errorCode) {
        super(message);
        this.errorCode = errorCode;
    }
    
    // Getters
}

// Usage:
throw new BusinessException("Invalid order status", "ORD-001");

📚 Advanced Topics

1. Response Status Codes

• Use @ResponseStatus annotation for default HTTP status

2. Validation Errors

• Special handling for @Valid failures

3. Internationalization

• Support for localized error messages

4. Error Codes

• Standardized error code system

5. Problem Details (RFC 7807)

• Standardized error response format