Introduction

Error handling is a critical aspect of any application. Spring Boot allows you to create custom exceptions and handle them gracefully. In this guide, we'll explore how to define and use custom exceptions in Spring Boot, complete with sample code and detailed explanations.

Prerequisites

Before you start, make sure you have the following prerequisites:

• A Spring Boot project (if you don't have one, follow the "Building a Spring Boot Web Application" tutorial)
• An Integrated Development Environment (IDE) like Spring Tool Suite, IntelliJ IDEA, or Visual Studio Code

Creating Custom Exceptions

You can create custom exceptions by extending the base RuntimeException class or any other exception class. Here's an example of a custom exception:

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

In this example, we create a custom exception named "CustomException" that extends RuntimeException and accepts a custom error message.

Throwing Custom Exceptions

You can throw custom exceptions in your code when specific error conditions are met. Here's an example of throwing the "CustomException" in a service method:

public String someServiceMethod() {
    if (errorCondition) {
        throw new CustomException("An error occurred.");
    }
    // Normal processing
    return "Result";
}
        

In this example, we throw the "CustomException" when an error condition is met. The exception message provides information about the error.

Handling Custom Exceptions

To handle custom exceptions, you can define an exception handler method in a controller advice. Here's an example of handling the "CustomException" and returning a custom error response:

@ControllerAdvice
public class CustomExceptionHandler {
    @ExceptionHandler(CustomException.class)
    public ResponseEntity<String> handleCustomException(CustomException ex) {
        return new ResponseEntity<>("Custom Error: " + ex.getMessage(), HttpStatus.BAD_REQUEST);
    }
}
        

In this example, we use the @ExceptionHandler annotation to handle the "CustomException" and return a custom error message with a 400 Bad Request status.

Conclusion

Custom exceptions play a vital role in error handling in Spring Boot applications. This guide covered creating custom exceptions, throwing them when needed, and handling them using a controller advice. With custom exceptions, you can provide more meaningful error messages and improve the robustness of your application.