Spring Boot custom exception handler
Exception handling is a very important aspect in a Spring Boot application. If you do not handle exceptions, your application may crash or exhibit unpredictable behavior. By default, Spring Boot returns uncaught exceptions to the client. This is usually not the desired behavior, as the exception message may not be understood by the client. In this article, we will describe how to implement custom exception handlers in Spring Boot applications for better exception handling.
Spring Boot exception handling mechanism
In a Spring Boot application, exception handling is handled by the Spring MVC framework. When a controller method throws an exception, Spring MVC will perform the following steps:
1. Search for a matching exception handler
2. Execute the matching exception handler
3. Return the processing result
The Spring MVC framework provides two default exception handlers:
1. DefaultHandlerExceptionResolver: Handle exceptions that come with the Spring MVC framework, such as MissingServletRequestParameterExceptionand HttpRequestMethodNotSupportedExceptionetc.
2. ResponseStatusExceptionResolver: Handle @ResponseStatusexceptions with annotations.
If your application needs to handle custom exceptions, you need to implement your own exception handler. Below we describe how to implement a custom exception handler in a Spring Boot application.
Implement a custom exception handler
To implement a custom exception handler, you need to perform the following steps:
1. Create a custom exception class, eg MyException.
public class MyException extends RuntimeException {
private static final long serialVersionUID = 1L;
public MyException(String message) {
super(message);
}
}
In the above code, we created a custom exception class MyException, inherited from RuntimeExceptionclass.
2. Create a custom exception handler, eg CustomExceptionHandler.
@ControllerAdvice
public class CustomExceptionHandler extends ResponseEntityExceptionHandler {
@ExceptionHandler(MyException.class)
public ResponseEntity<Object> handleMyException(MyException ex, WebRequest request) {
String errorMessage = ex.getMessage();
ErrorDetails errorDetails = new ErrorDetails(new Date(), errorMessage, request.getDescription(false));
return new ResponseEntity<>(errorDetails, HttpStatus.INTERNAL_SERVER_ERROR);
}
}
In the code above, we created a custom exception handler CustomExceptionHandler, marked with @ControllerAdvicean annotation. This annotation indicates that this class will be used for global exception handling.
We use @ExceptionHandlerannotations to mark MyExceptionmethods that handle exceptions. In this method, we encapsulate the error message, timestamp and request description into ErrorDetailsan object, and return it to the client as a response.
3. Throw a custom exception in the controller method.
@RestController
public class MyController {
@GetMapping("/test")
public String test() {
throw new MyException("This is a custom exception.");
}
}
In the above code, we /testare throwing the exception in the controller method of the interface MyException.
Now, the provider /testwill trigger MyExceptionan exception, which will then CustomExceptionHandlerbe caught and handled, and an error message returned to the client.
Test custom exception handler
In order to test custom exception handlers, we can use tools such as Postman or curl /testto send GET requests to the interface.
GET http://localhost:8080/test
If everything worked, you should see the following response:
{
"timestamp": "2023-05-30T08:00:00.000+00:00",
"message": "This is a custom exception.",
"details": "uri=/test"
}
This response contains CustomExceptionHandlerthe error message, timestamp, and request description we defined in .
Summarize
In this article, we covered how to implement custom exception handlers in Spring Boot applications. In order to implement a custom exception handler, you need to create a custom exception class, a custom exception handler, and throw the custom exception into the controller method. The custom exception handler will catch and handle the exception, and return the error message to the client.
By using custom exception handlers, you can better handle exceptions and provide more useful error messages to clients. This will help improve application reliability and availability.