How to create a handler for exceptions in a Spring Boot application

Introduction:
In any robust Spring Boot application, handling exceptions is crucial to provide a seamless user experience and ensure the stability of your system. In this blog post, we’ll guide you through the process of creating a custom exception handler in Spring Boot. By the end of this tutorial, you’ll be equipped with the knowledge to gracefully handle and respond to exceptions in your application.

SECTION 1: Creating the Custom Exception Class

1. Start by creating a new Java class, such as CustomException, to represent your custom exception.
2. Extend the appropriate exception class based on your scenario, such as RuntimeException or Exception, to ensure it behaves as expected.
3. Add any necessary constructors and methods to customize the exception behavior and provide relevant information.

SECTION 2: Implementing the Exception Handler

1. Create a new class, such as CustomExceptionHandler, to implement the exception handling logic.
2. Annotate the class with @RestControllerAdvice to indicate that it’s an exception handler.
3. Use @ExceptionHandler to define methods that handle specific exceptions.
4. In each exception handler method, specify the exception type as the method parameter.
5. Within the handler method, customize the response, error messages, and status code according to your application’s requirements.
6. You can return a custom error response object or utilize the built-in ResponseEntity to provide a consistent response format.

SECTION 3: Global Exception Handling

1. To handle exceptions globally, create a new method in the CustomExceptionHandler class and annotate it with @ExceptionHandler(Exception.class).
2. This method will catch any unhandled exceptions in your application.
3. Customize the response and error handling for these generic exceptions, ensuring they are properly logged and returned to the client.

SECTION 4: Registering the Exception Handler

1. Add the @ControllerAdvice annotation to your CustomExceptionHandler class to make it available throughout your application.
2. In your main application class, include the @EnableWebMvc annotation to enable the exception handling mechanism.
3. Spring Boot will automatically detect and register the exception handler, making it ready to handle exceptions thrown within your application.

SECTION 5: Testing the Exception Handler

1. Create test cases to ensure the exception handling functionality is working as expected.
2. Simulate various scenarios by throwing exceptions and validating the responses received.
3. Use testing frameworks like JUnit and Mockito to facilitate your testing process.

CONCLUSION:  Congratulations! You’ve successfully created a custom exception handler in your Spring Boot application. By implementing this exception handling mechanism, you can gracefully handle exceptions, provide informative error messages, and maintain the stability and usability of your application. Remember to continually test and refine your exception handling logic to ensure it aligns with your application’s requirements.