Custom Spring annotation for request parameters

Question

I would like to write custom annotations, that would modify Spring request or path parameters according to annotations. For example instead of this code:

@RequestMapping(method = RequestMethod.GET)
public String test(@RequestParam("title") String text) {
   text = text.toUpperCase();
   System.out.println(text);
   return "form";
}

I could make annotation @UpperCase :

@RequestMapping(method = RequestMethod.GET)
   public String test(@RequestParam("title") @UpperCase String text) {
   System.out.println(text);
   return "form";
}

Is it possible and if it is, how could I do it ?

Answer 1

As the guys said in the comments, you can easily write your annotation driven custom resolver. Four easy steps,

1. Create an annotation e.g.

---

@Target(ElementType.PARAMETER)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface UpperCase {
    String value();
}

2. Write a resolver e.g.

---

public class UpperCaseResolver implements HandlerMethodArgumentResolver {

    public boolean supportsParameter(MethodParameter parameter) {
        return parameter.getParameterAnnotation(UpperCase.class) != null;
    }

    public Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer, NativeWebRequest webRequest,
            WebDataBinderFactory binderFactory) throws Exception {
        UpperCase attr = parameter.getParameterAnnotation(UpperCase.class);
        return webRequest.getParameter(attr.value()).toUpperCase();
    }
}

3. register a resolver

---

<mvc:annotation-driven>
        <mvc:argument-resolvers>
            <bean class="your.package.UpperCaseResolver"></bean>
        </mvc:argument-resolvers>
</mvc:annotation-driven>

or the java config

    @Configuration
    @EnableWebMvc
    public class Config extends WebMvcConfigurerAdapter {
    ...
      @Override
      public void addArgumentResolvers(List<HandlerMethodArgumentResolver> argumentResolvers) {
          argumentResolvers.add(new UpperCaseResolver());
      }
    ...
    }

4. use an annotation in your controller method e.g.

---

public String test(@UpperCase("foo") String foo)