4 使用原有的Dao方式开发

4 使用原有的Dao方式开发

张创琦 2022.03.12

建立 ThreadLocal
1. 测试案例1：

threadLocal 是线程安全的，而 list 是线程不安全的

package com.kkb.test;
import org.apache.ibatis.session.SqlSession;
import java.util.ArrayList;
import java.util.List;
public class ThreadLocalTest {
    // 可以理解为一个容器，特殊点：只能盛放一个数据
    private ThreadLocal<String> threadLocal = new ThreadLocal<>();
    private List<String> list = new ArrayList<String>();
    public static void main(String[] args) {
        ThreadLocalTest test = new ThreadLocalTest();
        // 添加数据
        test.threadLocal.set("zcq");
        test.threadLocal.set("jby"); // 再次添加添加会覆盖前面的值
        // 取出数据
        String s = test.threadLocal.get();
        System.out.println(s);
    }
}

运行结果：

jby

2. 测试案例2：

package com.kkb.test;
import org.apache.ibatis.session.SqlSession;
import java.util.ArrayList;
import java.util.List;
public class ThreadLocalTest {
    // 可以理解为一个容器，特殊点：只能盛放一个数据
    private ThreadLocal<String> threadLocal = new ThreadLocal<>();
    private List<String> list = new ArrayList<String>();
    class MyThread1 extends Thread {
        @Override
        public void run() {
            threadLocal.set("jiabaoyu1"); // ThreadLocal 线程安全
            list.add("aaaa"); // 线程不安全
            System.out.println("MyThread1---threadLocal---"+threadLocal.get());
            System.out.println("MyThread1---list---"+list.get(0));
        }
    }
    class MyThread2 extends Thread {
        @Override
        public void run() {
            threadLocal.set("lindaiyu2");
            list.add("bbbb");
            System.out.println("MyThread2---threadLocal---"+threadLocal.get());
            System.out.println("MyThread2---list---"+list.get(0));
        }
    }
    public static void main(String[] args) {
        ThreadLocalTest test = new ThreadLocalTest();
        MyThread1 t1 = test.new MyThread1();
        MyThread2 t2 = test.new MyThread2();
        t1.start();
        t2.start();
    }
}

运行结果：

MyThread1---threadLocal---jiabaoyu1
MyThread2---threadLocal---lindaiyu2
MyThread2---list---aaaa
MyThread1---list---aaaa // 解释: 值被覆盖了

创建 utils 类

package com.kkb.utils;
import org.apache.ibatis.io.Resources; import org.apache.ibatis.session.SqlSession;
import  org.apache.ibatis.session.SqlSessionFactory; import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import java.io.IOException;
import java.io.Reader;
/**
 * ClassName: SessionUtil
 * 连接操作的工具类
 * @author wanglina
 * @version 1.0
 */
public class MybatisUtil {
    private static ThreadLocal<SqlSession> threadLocal = new ThreadLocal<SqlSession>();
    private static SqlSessionFactory SqlSessionFactory;
    /**
     *
     * 加载配置文件
     */ static{
        try{
            Reader reader = Resources.getResourceAsReader("mybatis.xml");
            SqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
        }catch(IOException e){ e.printStackTrace();
            throw new RuntimeException(e);
        }
    }
    /**
     *获取SqlSession
     *@return
     */
    public static SqlSession getSqlSession(){
        //从当前线程获取
        SqlSession sqlSession = threadLocal.get();
        if(sqlSession == null){
            // 创建sqlSession
            sqlSession = SqlSessionFactory.openSession();
            //将sqlSession与当前线程绑定
            threadLocal.set(sqlSession);
        }
        return sqlSession;
    }
    /**
     *关闭Session
     */
    public static void closeSqlSession(){
        //从当前线程获取
        SqlSession sqlSession = threadLocal.get();
        if(sqlSession != null){
            sqlSession.close(); threadLocal.remove();
        }
    }
}

编写 Dao 接口和 Dao 的实现类

package com.kkb.dao;
import com.kkb.pojo.Team;
import java.util.List;
// 原有的Dao的写法
public interface TeamDao {
    List<Team> queryAll();
    Team queryById(Integer teamId);
    int add(Team team);
    int update(Team team);
    int del(Integer teamId);
}

package com.kkb.dao;
import com.kkb.pojo.Team;
import com.kkb.utils.MybatisUtil;
import org.apache.ibatis.session.SqlSession;
import java.util.List;
public class TeamDaoImpl implements TeamDao {
    // 查询所有球队
    @Override
    public List<Team> queryAll() {
        SqlSession sqlSession = MybatisUtil.getSqlSession();
        List<Team> teamList = sqlSession.selectList("com.kkb.pojo.Team.findAll");
        return teamList;
    }
    // 根据id查询单个球队
    @Override
    public Team queryById(Integer teamId) {
        SqlSession sqlSession = MybatisUtil.getSqlSession();
        Team team = sqlSession.selectOne("com.kkb.pojo.Team.queryById", teamId);
        return team;
    }
    // 添加球队
    @Override
    public int add(Team team) {
        SqlSession sqlSession = MybatisUtil.getSqlSession();
        int num = sqlSession.insert("com.kkb.pojo.Team.add", team);
        sqlSession.commit();
        return num;
    }
    //更新球队
    @Override
    public int update(Team team) {
        SqlSession sqlSession = MybatisUtil.getSqlSession();
        int num = sqlSession.insert("com.kkb.pojo.Team.update", team);
        sqlSession.commit();
        return num;
    }
    // 根据id删除球队
    @Override
    public int del(Integer teamId) {
        SqlSession sqlSession = MybatisUtil.getSqlSession();
        int num = sqlSession.insert("com.kkb.pojo.Team.del", teamId);
        sqlSession.commit();
        return num;
    }
}

编写测试类

package com.kkb.test;
import com.kkb.dao.TeamDao;
import com.kkb.dao.TeamDaoImpl;
import com.kkb.pojo.Team;
import org.junit.Test;
import java.util.Date;
import java.util.List;
/**
 *ClassName: TestTeam
 *测试类
 *@author wanglina
 *@version 1.0
 */
public class TestTeamDao {
    private TeamDao teamDao=new TeamDaoImpl();
    // 成功
    @Test
    public void testDel(){
        int num = teamDao.del(1058);
        System.out.println(num);
    }
    // 成功
    @Test
    public void testUpdate(){
        Team team = teamDao.queryById(1054);
        team.setTeamName("lina");
        team.setLocation("bj");
        int num = teamDao.update(team);
        System.out.println(num);
    }
    // 会乱码
    @Test
    public void testAdd(){
        Team team=new Team();
        team.setTeamName("lina的球队");
        team.setLocation("北京");
        team.setCreateTime(new Date());
        int num = teamDao.add( team);
        System.out.println(num);
    }
    // 成功
    @Test
    public void test02(){
        Team team = teamDao.queryById(1001);
        System.out.println(team);
    }
    // 成功
    @Test
    public void test01(){
        List<Team> teams = teamDao.queryAll();
        teams.forEach(team -> System.out.println(team));
    }
}