使用spring RestController对错误请求的自定义响应

Question

I have the following controller. I am using Spring to create Restful APIs.

@RestController
public class UserController extends RestControlValidator {

@RequestMapping(value = "/user/", method = RequestMethod.POST, headers = "Accept=application/json", consumes = "application/json", produces = MediaType.APPLICATION_JSON_VALUE)
public @ResponseBody List newUser(@RequestBody @Valid UserInput input,BindingResult result) 
            {Some code}

}

The UserInput class looks like this:

public class UserInput{

    @NotEmpty
    private String emailId;
    @NotEmpty
    private String fName;
    private String lName;
    private int sex;

//getters and setters

Now when I try and access /user/ with data {"sex":"Male"} , I get the following response:

I want the response in case of such a request to be:

{"errors":{"sex":"The value must be an integer"}}

Is there any way of customising BAD REQUEST responses in Spring?

Answer 1

Considering the current scenario the most ideal solution would be to alter the behavior of HandlerMethodArgumentResolve as the json to pojo constructed by @RequestBody fails because we dont get a chance to check the wrong data and this check can very well be done in the custom message converter

A. first we would need to create LanguageMessageConverter as follows

public class LanguageMessageConverter extends
        AbstractHttpMessageConverter<Language> {
    private Gson gson = new Gson();
public LanguageMessageConverter() {
    super(new MediaType("application", "json", Charset.forName("UTF-8")));
}

@Override
protected boolean supports(Class<?> clazz) {
    return Language.class.equals(clazz);
}

Map<String, String> mp = new HashMap<>();

@Override
protected Language readInternal(Class<? extends Language> clazz,
        HttpInputMessage httpInputMessage) throws IOException,
        HttpMessageNotReadableException {
    Map langmp = gson.fromJson(
            convertStreamToString(httpInputMessage.getBody()), Map.class);

        for (Field field : clazz.getDeclaredFields()) {

            if (!langmp.get(field.getName()).getClass().getCanonicalName().equals(field.getType().getCanonicalName())) {
                if (field.getType().getCanonicalName().equals("java.lang.Integer")||field.getType().getCanonicalName().toString().equals("int")) {
                    langmp.put(field.getName(), "0");
                } else if (field.getType().equals("java.lang.String")) {
//TODO COde needs to be improved here because this check is not efficient
                    langmp.put(field.getName(), "wrong");
                }
            }
        }       
        Language lang = gson.fromJson(gson.toJson(langmp), clazz);
        return lang;
    }

1. we need to set the media type new MediaType("application", "json", Charset.forName("UTF-8")) which will make sure this class intervenes the mentioned MIME type
2. Considering we need to manipulate the result I found it best to convert it to map langmp (There are better JSON Parsers which can be used)
3. Since we need to to understand the existing type I used reflection api to get the fields via getDeclaredFields()
4. Using the above made the logical check using the datatype to understand if the type is incorrect for eg if the field datatype is int and if it is found as String then corresponding map value will be substituted
5. once that is done the map will hold the updated values where in if the data was wrong a default value would be set eg if the int var is set to 0 since the originating json had a String in it.
6. Once that is done the updated map is converted to the concerned class.

B. Secondly we need to register the custom MessageConverter in the dispatcher xml ie LanguageMessageConverter

<mvc:annotation-driven >
   <mvc:message-converters register-defaults="true">       
       <bean class="com.comp.org.controller.LanguageMessageConverter" />
    </mvc:message-converters>
</mvc:annotation-driven>

1. register-defaults="true" is very important since we are adding Custom MessageConverter but we also need the other existing converters working along with the one we have added
2. LanguageMessageConverter needs to be registered here.

C. Considering the concerned pojo is populated with the necessary details it would reach our controller post processing in the custom converter now we would add the manual validation eg. if the int variable has 0 the necessary error json should be returned

As per your request even if the json consists of the wrong data the custom message converter should process it and accordingly in the controller we can validate the condition mentioned. The code definitely can be improved further. Kindly let me know if this solution fulfilled your requirement or any part of the code requires further elaboration and hopefully addressed your concern.

Answer 2

I had the same issue, than I solved that way:

1. Create an Object called Error, like that (don't forget to implement Serializable...):

    private String fieldName; private String errorCode; private String defaultMessage; public Error() { } public Error(String fieldName, String errorCode, String defaultMessage) { this.fieldName = fieldName; this.errorCode = errorCode; this.defaultMessage = defaultMessage; } /* getters, setters */ 

2. Inside the @RestController method you ave to call inputValidator.validate() method (if you didn't create an Object Validator for your UserInput then we're really don't speaking the same language...)

    // validating the userInput userInputValidator.validate(userInput, bindingResult); if (bindingResult.hasErrors()) { List<Error> errors = new ArrayList<>(bindingResult.getErrorCount()); for (FieldError fieldWithError : bindingResult.getFieldErrors()) { errors.add(new Error(fieldWithError.getField(), fieldWithError.getCode(), fieldWithError.getDefaultMessage())); } return errors; } // in case of success: return null; 

3. Finally you'll have to translate the JSON object to your client side. You'll have two kind of objects:

   3.1. null ( undefined depending on the language you're using)

   3.2. A JSON object like that:

    [ { "fieldName": "name", "errorCode": "user.input.name.in.blank", "defaultMessage": "Insert a valid name!" }, { "fieldName": "firstPhone", "errorCode": "user.input.first.phone.blank", "defaultMessage": "Insert a valid first phone!" } ]