json与类，集合的转换（三）之Jackson实现

import org.apache.commons.collections.map.HashedMap;
import org.codehaus.jackson.map.ObjectMapper;
import org.codehaus.jackson.type.JavaType;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;

public class JacksonTest {

    public static void main(String[] args) throws IOException {
        //构建用户对象
        User guestUser = new User();
        guestUser.setName("admin");
        guestUser.setAge(18);
        User rootUser = new User();
        rootUser.setName("root");
        rootUser.setAge(18);

        //构建用户组对象 用户组中有admin用户和root用户
        UserGroup group = new UserGroup();
        group.setName("usergroup");
        group.getUsers().add(guestUser);
        group.getUsers().add(rootUser);

        //用户组对象转json
        ObjectMapper objectMapper = new ObjectMapper();
        String jsonString = objectMapper.writeValueAsString(group);
        System.out.println(jsonString);
        //json字符串转用户组对象
        UserGroup userGroup = objectMapper.readValue(jsonString,UserGroup.class);
        System.out.println(userGroup);

        //构建用户对象组
        //list转json
        List<User> userList = new ArrayList<User>();
        userList.add(guestUser);
        userList.add(rootUser);
        String jsonString1 = objectMapper.writeValueAsString(userList);
        System.out.println(jsonString1);
        //json转复杂类型List
        //Jackson处理一般的JavaBean和Json之间的转换只要使用ObjectMapper 对象的readValue和writeValueAsString两个方法就能实现。
        // 但是如果要转换复杂类型Collection如 List<YourBean>，那么就需要先反序列化复杂类型 为泛型的Collection Type。
        JavaType javaType = objectMapper.getTypeFactory().constructParametricType(ArrayList.class,User.class);
        List<User> users1 = (List<User>) objectMapper.readValue(jsonString1,javaType);
        System.out.println(users1);
        Map<String,User> map = new HashedMap();
        map.put(guestUser.getName(),guestUser);
        map.put(rootUser.getName(),rootUser);
        //map转json
        String jsonString2 = objectMapper.writeValueAsString(map);
        System.out.println(jsonString2);
        //第一次参数map类 后两个参数是map的键值类型的class
        JavaType javaTypeMap = objectMapper.getTypeFactory().constructParametricType(Map.class,String.class,User.class);
        Map<String,User> map1 = (Map<String, User>) objectMapper.readValue(jsonString2,javaTypeMap);
        System.out.println(map1.get("root").getAge());

    }
}