SpringMVC ArgumentREsoler(方法参数解析器)

Posted 2021-12-06 lxx-1843693653

例:

先创建自定义注解

//
@Target(ElementType.PARAMETER)
//在运行时生效
//RetentionPolicy.RUNTIME 给方法使用
@Retention(RetentionPolicy.RUNTIME)



public @interface CurrentUser {
}

去定义自定义注解的规则

package com.lanou.demo.resolvers;

import com.lanou.demo.annotation.CurrentUser;
import com.lanou.demo.bean.UserBean;
import org.springframework.core.MethodParameter;
import org.springframework.stereotype.Component;
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;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;

@Component
public class CurrentUserArgumentResolver implements HandlerMethodArgumentResolver {

    /*定义一个规则,
     *当前的参数解析器可以处理哪个Controller方法的哪个参数
     *返回是true  表示对这个参数进行处理
     * */
    @Override
    public boolean supportsParameter(MethodParameter parameter) {
        //定义自己的规则
        //1.参数被@CurrentUser注解所标记
           CurrentUser currentUser
                  = parameter.getParameterAnnotation(CurrentUser.class);

        //2.参数类型为UserBean类型
        Class<?> clazz = parameter.getParameterType();

        return parameter.hasParameterAnnotation(CurrentUser.class)
                && UserBean.class == clazz;
    }

    /*如何为这个参数赋值
       这个方法的返回值会直接赋值给解析的参数
    */
    @Override
    public Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer, NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception {
        //获取请求
        HttpServletRequest req = webRequest.getNativeRequest(HttpServletRequest.class);
        //获取session
        HttpSession session = req.getSession();
        //把user存进session
        Object user = session.getAttribute("user");
        //返回
        return user;
    }
}

在xmlzhong把自定义注解配置上

把它改成开放标签
<mvc:annotation-driven/>

例:
 <mvc:annotation-driven>
        <mvc:argument-resolvers>
            <!--配置的哪个类-->
            <ref bean="currentUserArgumentResolver"/>
        </mvc:argument-resolvers>
  </mvc:annotation-driven>

这样就可以使用自定义注解了

@RequestMapping("/insert1")
    @ResponseBody
    public String insert1(String name, String author, Float price,@CurrentUser UserBean user) {
        // 直接在方法的参数中添加形参, 参数名即为前端form中input的name属性
        System.out.println(name);
        System.out.println(author);
        System.out.println(price);
        return "insert1";
    }