Spring rest application and exception localization

Issue

I am developing a spring boot app with restful services and angularjs as front end. The application must support multiple languages. One of the things I am having problem is the business exceptions thrown from my services. E.g. I have a book service which may throw an exception like this

if (book == null) {
        throw new ServiceException("The book you are looking for no longer exist");
}

What is the best approach to localize them?

Solution

You have to use @RestControllerAdvice to seprate your exception handling logic from your business code. As per @ControllerAdvice doc, the methods defined in the class annotated as @ControllerAdvice apply globally to all Controllers. @RestControllerAdvice is just a convenience class equal to (@RestControllerAdvice = @ControllerAdvice + @ResponseBody). Please check below class:

@RestControllerAdvice
public class GenericExceptionHandler {

    @Autowired
    private MessageSource messageSource;

    @ExceptionHandler(ServiceException.class)
    public ResponseEntity<ErrorResponse> handle(ServiceException.class e, Locale locale) {

            String errorMessage = messageSource.getMessage(
                                "error.message", new Object[]{},locale);  
            
            ErrorResponse error = new ErrorResponse();
            error.setErrorCode(HttpStatus.BAD_REQUEST.value());
            error.setMessage(errorMessage);
        

            return new ResponseEntity<>(error, HttpStatus.BAD_REQUEST);
    }
}

// other Custom Exception handlers

Your ErrorResponse is normal javabean as below:

public class ErrorResponse{

private int errorCode;
private String message;

//getter and setter
}

And you should have MessageSource configured in your configuration to read the locale specific error messages as below:

@Configuration
public class MessageConfig {

    @Bean
    public MessageSource messageSource() {
        ResourceBundleMessageSource source = new ResourceBundleMessageSource();
        source.setBasename("i18n/messages");
        source.setUseCodeAsDefaultMessage(true);
        return source;
    }
}

Answered By - Sangam Belose