为@RequestMapping标注的方法扩展其传入参数

从Spring3.1开始有了HandlerMethodArgumentResolver接口，可以为@RequestMapping标注的方法扩展其传入参数。

首先，自定义注解CurrentUser

@Target({ElementType.PARAMETER})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface CurrentUser {
 
	/**
     * 当前用户在request中的名字 默认user
     *
     * @return
     */
    String value() default "user";
}

然后，实现HandlerMethodArgumentResolver接口

import org.springframework.core.MethodParameter;
import org.springframework.web.bind.support.WebDataBinderFactory;
import org.springframework.web.context.request.NativeWebRequest;
import org.springframework.web.method.support.HandlerMethodArgumentResolver;
import org.springframework.web.method.support.ModelAndViewContainer;
 
public class CurrentUserMethodArgumentResolver implements HandlerMethodArgumentResolver {
 
    public CurrentUserMethodArgumentResolver() {
    }
 
    @Override
    public boolean supportsParameter(MethodParameter parameter) {
        if (parameter.hasParameterAnnotation(CurrentUser.class)) {
            return true;
        }
        return false;
    }
 
    @Override
    public Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer, NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception {
        CurrentUser currentUserAnnotation = parameter.getParameterAnnotation(CurrentUser.class);
        return webRequest.getAttribute(currentUserAnnotation.value(), NativeWebRequest.SCOPE_REQUEST);
    }
}

在Spring-MVC的配置文件中加入以下配置：

<mvc:annotation-driven>
    <mvc:argument-resolvers>
        <bean class="xx.xx.xx.CurrentUserMethodArgumentResolver" />
    </mvc:argument-resolvers>
</mvc:annotation-driven>

这样，你就可以在有@RequestMapping标注的的方法中使用了，如

    @RequestMapping(value = "index")
    public String index(@CurrentUser User user, Model model) {
        System.out.println(user.getUsername());
        return "admin/index";
    }