Custom Exception Handling For Spring Boot Rest Controller

There can be a scenario where we want to send a custom success or error message as a response to the Rest API call.

This can be easily achievable using @ControllerAdvice annotation by implementing Custom Exception Handler. It can be either global error message or controller level messages. Here I am going to explain how to implement a global exception handler in spring boot.

Below are the steps to implement custom error response in Spring boot Rest Controller 

1.  Implement a custom exception handler by extending ResponseEntityExceptionHandler with @ControllerAdvice annotation.
2. Implement a Custom Exception. 
3. Design a CustomApiException Response Model.
4. Throw custom exception from Rest Service.

Step 1 - Implementing a Custom Exception Handler

When implementing a custom exception handler either you can implement a custom method to handle the exception or override the default "handleException" method 

Example to implement a custom exception handler method 

Below exception handler method "handleNoProductsFoundException" handles  "NoProductFoundException" which is the custom exception I am going to create in Step 2 

@ControllerAdvice
public class CustomExceptionHandler extends ResponseEntityExceptionHandler {

    @ExceptionHandler(NoProductFoundException.class)
    public final ResponseEntity<ApiExceptionResponse> handleNoProductsFoundException(NoProductFoundException ex, WebRequest request) {
        ApiExceptionResponse apiExceptionResponse = new ApiExceptionResponse(new Date(), ex.getMessage(),
                request.getDescription(false));
        return new ResponseEntity<>(apiExceptionResponse, HttpStatus.NOT_FOUND);

    }

}

Step 2 -  Implementing custom exception 

Custom Exception should be created by extending "RuntimeException"

public class NoProductFoundException extends RuntimeException {
    public NoProductFoundException(String exception) {
        super(exception);
    }
}

Step 3 - Custom API Exception Model 

Design a custom API exception response model with the properties whichever need to be returned like error message, date and time etc...

import java.util.Date;

public class ApiExceptionResponse {
    private Date timestamp;
    private String message;
    private String details;

    public ApiExceptionResponse(Date timestamp, String message, String details) {
        super();
        this.timestamp = timestamp;
        this.message = message;
        this.details = details;
    }

    public Date getTimestamp() {
        return timestamp;
    }

    public String getMessage() {
        return message;
    }

    public String getDetails() {
        return details;
    }
}

Step 4 - Throw Custom Exception From Rest Service

Throw the custom exception implemented from Rest Service where ever needed using "throw new".

@Service
public class ProductService {

    @Autowired
    ProductRepository productRepository;


    public List<Product> getAllProduct() {
        List<Product> products = productRepository.findAll();
        if (products.isEmpty()) {
            throw new NoProductFoundException("No products available");
        }
        return products;

    }

    public Product createProduct(Product product) {
        return productRepository.save(product);
    }
}

and that's it, we have implemented a global custom exception handler for the rest controller.

Complete source code for this example available at Git