Custom converter for @RequestParam in Spring MVC

Question

I am getting an encrypted String as Query parameter to a Spring rest controller method.

I wanted to decrypt the string before it reaches the method based on some annotat

Answer 1

HandlerMethodArgumentResolver would be the best in this regard.

1. Create your annotation:

---

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

2. Create your Custom HandlerMethodArgumentResolver:

---

public class DecryptResolver implements HandlerMethodArgumentResolver {

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

    @Override
    public Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer, NativeWebRequest webRequest,
            WebDataBinderFactory binderFactory) throws Exception {
        Decrypt attr = parameter.getParameterAnnotation(Decrypt.class);
        String encrypted = webRequest.getParameter(attr.value());
        String decrypted = decrypt(encrypted);

        return decrypted;
    }

    private String decrypt(String encryptedString) {
        // Your decryption logic here

        return "decrypted - "+encryptedString;
    }
}

3. Register the resolver:

---

@Configuration
@EnableMvc // If you're not using Spring boot
public class WebConfig extends WebMvcConfigurerAdapter {

    @Override
    public void addArgumentResolvers(List argumentResolvers) {
          argumentResolvers.add(new DecryptResolver());
    }
}

4. Voila, you have your decrypted parameter. Note that you won't need to use @RequestParam anymore.

---

@RequestMapping(value = "/customer", method = RequestMethod.GET)
public String getAppointmentsForDay(@Decrypt("secret") String customerSecret) {
System.out.println(customerSecret);  // Needs to be a decrypted value.
   ...
}