Handling custom exceptions (i18n) with Spring Data REST

Question

I'm using Spring Boot 1.5.4 with Spring JPA, Spring Data REST, HATEOAS... I'm looking for a best practice (Spring way) to customize exceptions Spring Data REST is managing adding the i18n support.

I looked at the class MessageException (https://github.com/spring-projects/spring-data-rest/blob/master/spring-data-rest-webmvc/src/main/java/org/springframework/data/rest/webmvc/support/ExceptionMessage.java) as start point.

A typical Spring Data REST exception is very nice:

    {
    "timestamp": "2017-06-24T16:08:54.107+0000",
    "status": 500,
    "error": "Internal Server Error",
    "exception": "org.springframework.dao.InvalidDataAccessApiUsageException",
    "message": "org.hibernate.TransientPropertyValueException: Not-null property references a transient value - transient instance must be saved beforeQuery current operation : com.test.server.model.workflows.WorkSession.checkPoint -> com.test.server.model.checkpoints.CheckPoint; nested exception is java.lang.IllegalStateException: org.hibernate.TransientPropertyValueException: Not-null property references a transient value - transient instance must be saved beforeQuery current operation : com.test.server.model.workflows.WorkSession.checkPoint -> com.test.server.model.checkpoints.CheckPoint",
    "path": "/api/v1/workSessions/start"
}

What I'm trying to do is:

1. Localize error and message fields (i18n)
2. possibly change the message text to something else (always localized)

I didn't find any reference in Spring Data REST doc about how to customize or localize exception (https://docs.spring.io/spring-data/rest/docs/current/reference/html/). I hope there is a elegant way to do that.

I added in my WebMvcConfigurerAdapter this:

@Bean
public LocaleResolver localeResolver() {
    return new SmartLocaleResolver();
}

public class SmartLocaleResolver extends CookieLocaleResolver {

    @Override
    public Locale resolveLocale(HttpServletRequest request) {
        String acceptLanguage = request.getHeader("Accept-Language");
        if (acceptLanguage == null || acceptLanguage.trim().isEmpty()) {
            return super.determineDefaultLocale(request);
        }
        return request.getLocale();
    }

}

@Bean
public ResourceBundleMessageSource messageSource() {
    ResourceBundleMessageSource source = new ResourceBundleMessageSource();
    source.setBasenames("i18n/messages"); // name of the resource bundle
    source.setUseCodeAsDefaultMessage(true);
    return source;
}

I guess I could be able to intercept exceptions in this way:

    @ControllerAdvice(annotations = RepositoryRestController.class)
public class GenericExceptionHandler {

    @ExceptionHandler
    public ResponseEntity handle(Exception e, Locale locale) {
          //missing part...
            return new ResponseEntity(exceptionMessageObject, new HttpHeaders(), httpStatus);
    }

Is there a way to put all together using Spring best practices?

Answer 1

@ControllerAdvice(annotations = RepositoryRestController.class)
public class GenericExceptionHandler {
    @Autowired
    private MessageSource messageSource;

    @ExceptionHandler
    //if you don't use Exception e in method you can remove it , live only Locale
    public ResponseEntity handle(Exception e, Locale locale) {

            String errorMessage = messageSource.getMessage(
                                 "error.message", new Object[]{},locale);  
            //set message  or return it instead of exceptionMessageObject
            exceptionMessageObject.setMessage(exceptionMessageObject);

            return new ResponseEntity(exceptionMessageObject, 
                   new HttpHeaders(), httpStatus);
    }

see spring doc 7.15.1 Internationalization using MessageSource

---

" how I should create exceptionMessageObject to be like the one Spring Data REST creates? "

create you own error wraper like :

public class CustomError {
    private HttpStatus status;
    private String message;
    private Exception originalException;//if you need it        
    // getter setter
}

"How to have different messages for different exceptions? Should I create a long if else chain checking the class of the exception? "

create resolver ,

private String resolveExceptionToMessage(Exception exceptio){
    //or put in map<Exceptio,String error.message.type1> 
    // String errorCode = map.get(excptio);
    //eturn messageSource.getMessage(errorCode , new Object[]{},locale);
    if(exceptio instanceof ....){
        return messageSource.getMessage("error.message.type1", new Object[]{},locale);
    }
    return "";
}

or use methods with @ExceptionHandler({ CustomException1.class }) , @ExceptionHandler({ CustomException1.class }).... and do put in each method just errror.code , all other part are similar

 @ExceptionHandler({ CustomException1.class})
    public ResponseEntity handleException1() {
        return createError(code for this exceptio 1);
    }
    @ExceptionHandler({ CustomException2.class})
    public ResponseEntity handleException2() {
        return createError(code for this exceptio 2);
    }
    private ResponseEntity createError(String errorCode ) {
            CustomError customError = new CustomError();
            customError.setHttpStatus(HttpStatus.BAD_REQUEST);
            String errorMessage = messageSource.getMessage(
                                 errorCode , new Object[]{},locale); 

            customError.setMessage(errorMessage );
            customError.setOriginalException(e);
            return new ResponseEntity<Object>(customError, new HttpHeaders(), 
                          customError.getStatus());
    }

How set httpStatus? I would like use the default status Spring Data REST use for commons exceptions...

public ResponseEntity handle(Exception e, Locale locale) {
        CustomError customError = new CustomError();
        customError.setHttpStatus(HttpStatus.BAD_REQUEST);
        customError.setMessage(resolveExceptionToMessage(e));
        customError.setOriginalException(e);
        return new ResponseEntity<Object>(customError, new HttpHeaders(), 
                      customError.getStatus());
}