Is it possible to get hold of the value of the parameter from MethodParameter object?

Question

I am extending the HandlerMethodArgumentResolver to get hold of a parameter annotated by a custom annotation

@RequestMapping(value = "/cases/{caseId}", params = "meta",
                method = PUT, produces = APPLICATION_JSON_VALUE)
@ResponseBody
@ResponseStatus(HttpStatus.OK)
public String updateUIMetadata(
    @RequestBody
    @JsonData(schemaLocation = "schema/metadata_schema.json")
    final String metadataJson) {
}

I want to get hold of the value in my string metadataJson in my class, specifically in the resolveArgument method. I know it has a MethodParameter parameter, but is it possible to get hold of the actual value of the parameter which is passed along with the web request?

public class UpdateMetadataInterceptor implements HandlerMethodArgumentResolver {


@Override
public boolean supportsParameter(MethodParameter parameter) {
    return parameter.hasParameterAnnotation(JsonData.class);
}

@Override
public String resolveArgument(MethodParameter parameter,
        ModelAndViewContainer mavContainer, NativeWebRequest webRequest,
        WebDataBinderFactory binderFactory) throws Exception {
    System.out.println("Inside UpdateMetadata");
    // TODO something with metadataJson

}
}

The purpose of `resolveArgument` is to **provide** the value that will be bound to the parameter. Spring will call your `UpdateMetadataInterceptor#resolverArgument`, gets its return value, and invoke `updateUIMetadata` with it. — Sotirios Delimanolis, Aug 21 '15 at 05:04
In this case, it doesn't make sense to annotate your parameter with both `@RequestBody` and `@JsonData`. Spring will use only one `HandlerMethodArgumentResolver` (the one for `@RequestBody`) to produce an argument. — Sotirios Delimanolis, Aug 21 '15 at 05:05
[Read this.](http://stackoverflow.com/questions/18944627/form-submit-in-spring-mvc-3-explanation/18944736#18944736) — Sotirios Delimanolis, Aug 21 '15 at 05:09
Thanks for the explanation. So what I want to do is intercept the method `updateUIMetadata`, extract the value of the parameter and do something with it before the method is invoked. And I want to do it without using aop. I guess I should use `HandlerInterceptor` then. Or is there a better way that you might be aware of? — rrrocky, Aug 21 '15 at 06:24
Spring MVC doesn't provide a way to intercept the arguments used to invoke your handler method. AOP seems appropriate. — Sotirios Delimanolis, Aug 21 '15 at 15:14
@SotiriosDelimanolis, I am still confused by your second comment. Can you please elaborate on it. — rrrocky, Aug 24 '15 at 13:08
The arguments are resolved after the `HandlerInterceptor` is invoked so you don't get access to them. I think AOP is the only _simple_ way to do this at the moment. — Sotirios Delimanolis, Aug 24 '15 at 14:33
But I have not used `HandlerInterceptor`. I am using `HandlerMethodArgumentResolver ` — rrrocky, Aug 24 '15 at 16:01

score 1 · Answer 1 · answered Aug 25 '15 at 11:48

HandlerMethodArgumentResolver is invoked only if Spring cannot resolve one or more of a method's arguments. In the above case, a simple String is annotated with @RequestBody. Hence, Spring will be able to resolve it from the web request. Thus HandlerMethodArgumentResolver will never get invoked. In order to achieve what I wanted, I followed the following strategy

Remove the @RequestBody annotation and club it with the @JsonData annotation

Now, since Spring does not know how to resolve metadataJson, it will invoke HandlerMethodArgumentResolver. Here, we need to implement the logic of @RequestBody to extract the string from the body of the web request. This I did as below:

public class ValidateJsonSchema implements HandlerMethodArgumentResolver {

@Bean
private RequestMappingHandlerAdapter requestMappingHandlerAdapter() {
return new RequestMappingHandlerAdapter();
}
private RequestResponseBodyMethodProcessor requestResponseBodyMethodProcessor = null;

@Override
public boolean supportsParameter(MethodParameter parameter) {
return parameter.hasParameterAnnotation(JsonData.class);
}

@Override
public String resolveArgument(MethodParameter parameter,
    ModelAndViewContainer mavContainer, NativeWebRequest webRequest,
    WebDataBinderFactory binderFactory) throws Exception {
String value = (String) getRequestResponseBodyMethodProcessor()
        .resolveArgument(parameter, mavContainer, webRequest, binderFactory);
// do something with value
return value;

}

private RequestResponseBodyMethodProcessor getRequestResponseBodyMethodProcessor() {

if (requestResponseBodyMethodProcessor == null) {
    List<HttpMessageConverter<?>> messageConverters = requestMappingHandlerAdapter().getMessageConverters();
    requestResponseBodyMethodProcessor = new RequestResponseBodyMethodProcessor(messageConverters);
}
return requestResponseBodyMethodProcessor;
}
}

I used RequestMappingHandlerAdapter to get the message converters and created a new instance of RequestResponseBodyMethodProcessor. Then I called the resolveArgument method of the same instance which returned the object, which I then cast to String

Is it possible to get hold of the value of the parameter from MethodParameter object?

1 Answers1