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 ?

Solution

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) 

Comments

[Sotirios Delimanolis]

Look at the HandlerMethodArgumentResolver interface.

[beerbajay]

You can also do this with spring AOP; you'd use a method annotated like @Before("@annotation(my.pkg.annotation.UpperCase)"), then transform the parameter in the method.

[wesker317]

Shouldn't it be : <bean class="your.package.UpperCaseResolver"></bean> ?

[hiway]

this answer needs a relative high version of springframework. I tried 4.1.4,does not work, 4.2.4 can work.

[Tushar Banne]

I created a custom annotation of my own. Used it in a sample application. It works fine. But when I tried to Integrate the same code with my project, it doesn't work. Not sure why is it not getting picked up

[NickGreen]

Works as expected in spring boot 1 with spring-web 4.3.14.RELEASE, thanks.

[Martin van Wingerden]

Since Spring 5 you should just implement the interface WebMvcConfigurer instead of extending (the now deprecated) WebMvcConfigurerAdapter

[tinker_fairy]

@master-slave i have used both the mvc:annotation/config but the custom resolver is not getting called in spring mvc project. It works in spring boot application. I dont know spring boot, is it related to spring boot?