项目用到，简单记录下使用方法：

package com.action;

import com.biz.IUserBiz;
import com.entity.UserEntity;
import com.opensymphony.xwork2.ActionSupport;

import java.util.List;
import java.util.HashMap;
import java.util.Map;

public class MapUserAction extends ActionSupport{private String loginName;
    private String loginPwd;

    //将会被Struts2序列化为JSON字符串的对象，必须有该属性的getter方法
    private Map<String, Object> dataMap;
    /* 构造方法 */
    public MapUserAction() {dataMap = new HashMap<>();    //初始化Map对象
    }public Map<String, Object> getDataMap() {return dataMap;
    }public void setLoginName(String loginName){this.loginName = loginName;
    }public void setLoginPwd(String loginPwd){this.loginPwd = loginPwd;
    }private IUserBiz userBiz;

    public void setUserBiz(IUserBiz userBiz){this.userBiz = userBiz;
    }/** 测试通过action以Struts2默认方式返回JSON数据 **/
    public String MapToJSON() throws Exception {List list = userBiz.login(loginName,loginPwd);
        if(list.size()>0){UserEntity user = (UserEntity)list.iterator().next();
            // dataMap中的数据将会被Struts2转换成JSON字符串，所以这里要先清空其中的数据
            dataMap.clear();
            dataMap.put("ID",user.getId());
            dataMap.put("Account",user.getAccount());
            dataMap.put("Name",user.getName());
            dataMap.put("Phone",user.getPhone());
            dataMap.put("Type",user.getType());
            if(user.getCarListByCar()!= null){dataMap.put("CarID",user.getCarListByCar().getCarId());
                dataMap.put("CarNum",user.getCarListByCar().getCarNum());
                dataMap.put("CarName",user.getCarListByCar().getCarName());
                dataMap.put("CarModel",user.getCarListByCar().getCarModel());
                dataMap.put("CarStatus",user.getCarListByCar().getCarStatus());
            }dataMap.put("loginStatus","True");
            return SUCCESS;
        }else {dataMap.clear();
            dataMap.put("loginStatus","False");
            return SUCCESS;
        }}
}

    <bean id ="userDao" class="com.dao.UserDaoImpl">
        <property name="sessionFactory" ref="sessionFactory"/>
    </bean>

    <bean id = "userBiz" class="com.biz.UserBiz">
        <property name="userDao" ref="userDao"/>
    </bean>

    <bean id="mapAction" class="com.action.MapUserAction" scope="prototype">
        <property name="userBiz" ref="userBiz"/>
    </bean>

<package name="json" extends="json-default" namespace="/Test">

    <action name="MapTest" class="mapAction" method="MapToJSON">
        <result type="json"><!--默认序列化返回所有getter方法-->
            <param name="root">dataMap</param><!-- root 返回 dataMap 注释掉将返回全部 -->

	    <!--<param name="excludeNullProperties">true</param>-->
	    <!--<param name="excludeProperties">loginPwd</param>-->

    </action>