Question

I have an controller that returns JSON. It takes a form, which validates itself via spring annotations. I can get FieldError list from BindingResult, but they don’t contain the text that a JSP would display in the <form:errors> tag. How can I get the error text to send back in JSON?

@RequestMapping(method = RequestMethod.POST)
public @ResponseBody JSONResponse submit(@Valid AnswerForm answerForm, BindingResult result, Model model, HttpServletRequest request, HttpServletResponse response) {
    if (result.hasErrors()) {
        response.setStatus(HttpServletResponse.SC_BAD_REQUEST);
        JSONResponse r = new JSONResponse();
        r.setStatus(JSONResponseStatus.ERROR);
        //HOW DO I GET ERROR MESSAGES OUT OF BindingResult??? 
    } else {
        JSONResponse r = new JSONResponse();
        r.setStatus(JSONResponseStatus.OK);
        return r;
    }
}

JSONREsponse class is just a POJO

public class JSONResponse implements Serializable {
    private JSONResponseStatus status;
    private String error;
    private Map<String,String> errors;
    private Map<String,Object> data;
    
    // ...getters and setters...
}

Calling BindingResult.getAllErrors() returns an array of FieldError objects, but it does not have the actual errors.

Answer 1

Disclaimer: I still do not use Spring-MVC 3.0

But i think the same approach used by Spring 2.5 can fullfil your needs

for (Object object : bindingResult.getAllErrors()) {
    if(object instanceof FieldError) {
        FieldError fieldError = (FieldError) object;

        System.out.println(fieldError.getCode());
    }

    if(object instanceof ObjectError) {
        ObjectError objectError = (ObjectError) object;

        System.out.println(objectError.getCode());
    }
}

I hope it can be useful to you

UPDATE

If you want to get the message provided by your resource bundle, you need a registered messageSource instance (It must be called messageSource)

<bean id="messageSource" class="org.springframework.context.support.ResourceBundleMessageSource">
    <property name="basenames" value="ValidationMessages"/>
</bean>

Inject your MessageSource instance inside your View

@Autowired
private MessageSource messageSource;

And to get your message, do as follows

for (Object object : bindingResult.getAllErrors()) {
    if(object instanceof FieldError) {
        FieldError fieldError = (FieldError) object;

        /**
          * Use null as second parameter if you do not use i18n (internationalization)
          */

        String message = messageSource.getMessage(fieldError, null);
    }
}

Your Validator should looks like

/**
  * Use null as fourth parameter if you do not want a default message
  */
errors.rejectValue("<FIELD_NAME_GOES_HERE>", "answerform.questionId.invalid", new Object [] {"123"}, null);