Spring Framework `@ExceptionHandler`

In Spring Framework, the `@ExceptionHandler` annotation is used to handle exceptions that occur during the execution of a controller method. This allows you to handle specific exceptions in a centralized manner without cluttering your code with `try-catch` blocks. You can define exception handler methods in your controller or in a global exception handler class.

 
Example of using @ExceptionHandler:

Let’s look at an example of how to use the `@ExceptionHandler` annotation in a Spring Boot application:
Create a custom exception class First, let's define a custom exception that we will handle in the controller.

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

Create a Controller that throws the exception In this step, we’ll create a simple controller that throws a `ResourceNotFoundException` when an endpoint is accessed.

 
import org.springframework.web.bind.annotation.GetMapping; import org.springframework.web.bind.annotation.RestController; @RestController public class MyController { @GetMapping("/resource/{id}") public String getResourceById(int id) { if (id <= 0) { throw new ResourceNotFoundException("Resource with ID " + id + " not found!"); } return "Resource found with ID " + id; } }

Handle the exception using `@ExceptionHandler`  Now, let’s handle the `ResourceNotFoundException` using the `@ExceptionHandler` annotation in the same controller.

 
import org.springframework.http.HttpStatus; import org.springframework.http.ResponseEntity; import org.springframework.web.bind.annotation.ExceptionHandler; import org.springframework.web.bind.annotation.RestControllerAdvice; @RestControllerAdvice public class GlobalExceptionHandler { @ExceptionHandler(ResourceNotFoundException.class) public ResponseEntity<String> handleResourceNotFoundException(ResourceNotFoundException ex) { return new ResponseEntity<>(ex.getMessage(), HttpStatus.NOT_FOUND); } }

 
Running the Application When you run this Spring Boot application and access the /resource/{id} endpoint with an invalid ID (e.g., `/resource/0` or `/resource/-1`), it will return a response like:
HTTP Status: 404 Not Found Body: Resource with ID 0 not found!
Example Output:

• - When accessing `/resource/1`, it will return "Resource found with ID 1". 
• - When accessing `/resource/0`, it will return a 404 response with the message "Resource with ID 0 not found!".

Advantages of using @ExceptionHandler:
 Centralized exception handling. - Cleaner code with no need for `try-catch` blocks in each controller method. 

 Ability to return custom error responses with HTTP status codes. You can handle multiple exceptions in a similar way by adding more `@ExceptionHandler` methods in the same class, or even define exception handling globally for all controllers using `@ControllerAdvice` instead of `@RestControllerAdvice`.