How do you create a global exception handler in Spring Boot?

Table of Contents

Introduction

In a Spring Boot application, handling exceptions effectively is essential for providing meaningful error messages and preventing the application from crashing unexpectedly. A global exception handler allows you to manage exceptions across all controllers in a centralized manner. This ensures that error handling is consistent, reduces boilerplate code, and simplifies maintenance. Using Spring's @ControllerAdvice and @ExceptionHandler annotations, you can create a global exception handler to catch and manage exceptions globally.

Steps to Create a Global Exception Handler in Spring Boot

Step 1: Use @ControllerAdvice to Define a Global Exception Handler

@ControllerAdvice is a specialization of the @Component annotation in Spring, allowing you to define global error handling logic. When you annotate a class with @ControllerAdvice, Spring Boot will automatically detect it and apply its error handling to all controller classes.

Example: Create a Global Exception Handler

In this example:

  • @ControllerAdvice is used to define a class that will handle exceptions globally across all controllers.
  • @ExceptionHandler(ResourceNotFoundException.class) catches the custom ResourceNotFoundException and returns a custom error response with a 404 Not Found status.
  • @ExceptionHandler(Exception.class) catches generic exceptions and returns a 500 Internal Server Error status.

Step 2: Define the Error Response Class

To send a detailed error response, you can create a custom ErrorResponse class that will be used to structure the error message.

Example: ErrorResponse Class

In this example:

  • The ErrorResponse class includes fields such as timestamp, status, error, message, and path.
  • This structure is used to send detailed error responses to the client, helping to understand what went wrong.

Step 3: Throw Custom Exceptions in Your Controller

You can throw custom exceptions in your controller methods based on specific business logic. These exceptions will be caught by the global exception handler.

Example: Throwing a Custom Exception in a Controller

In this example:

  • If the id is invalid (less than or equal to 0), a ResourceNotFoundException is thrown.
  • This exception will be caught by the handleResourceNotFound method in the GlobalExceptionHandler class.

Step 4: Customize Exception Handling for Other Scenarios

You can customize your exception handling for other common scenarios, such as validation errors, access denied, or bad input. Simply create specific exception classes and handle them in the global handler.

Example: Handling Invalid Input

In this example:

  • The InvalidInputException is handled and a 400 Bad Request status is returned with a custom error message.

Step 5: Handle Global Exceptions for Unhandled Errors

If you want to handle any unhandled exceptions (i.e., those not covered by a specific exception handler), you can define a generic exception handler.

In this example:

  • Any exception not explicitly caught by other methods will be handled by this generic handler, returning an HTTP 500 response with a general error message.

Step 6: Test Your Global Exception Handler

To test the global exception handler, you can trigger exceptions in your controller or service layers and ensure that the corresponding error responses are returned.

  • Access /products/0 to trigger the ResourceNotFoundException.
  • Access /products/invalid to test invalid input handling.

Spring Boot will automatically apply the appropriate exception handler and return a structured error response to the client.

Conclusion

Creating a global exception handler in Spring Boot using @ControllerAdvice and @ExceptionHandler provides a centralized way to manage errors across all controllers. It allows you to handle specific exceptions with custom messages, HTTP status codes, and response bodies. This approach ensures consistency in error responses, improves code readability, and simplifies error management in large Spring Boot applications. By defining custom exceptions and error responses, you can provide clients with more meaningful feedback, which is crucial for debugging and troubleshooting.

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