手撕ThreadLocal源码

1. 图解  72

2. 代码  72

代码在com.powernode.threadlocal

Test

package com.powernode.threadlocal;

//这里是主main方法  72

public class Test {
    public static void main(String[] args) {
        //获取Thread对象
        Thread thread = Thread.currentThread();
        System.out.println(thread);
        

        //调用service
        UserService userService = new UserService();
        userService.save();
    }
}

UserService

package com.powernode.threadlocal;

//一个service类  72
public class UserService {
    private UserDao userDao = new UserDao();
    //提供一个方法
    public void save(){
        //获取Thread对象
        Thread thread = Thread.currentThread();
        System.out.println(thread);

        //得到connection
        Connection connection = DBUtil.getConnection();
        System.out.println(connection);

        //调用UserDao中的insert方法
        userDao.insert();
    }
}

UserDao

package com.powernode.threadlocal;

//一个Dao类  72
public class UserDao {
    public void insert(){
        //获取Thread对象
        Thread thread = Thread.currentThread();
        System.out.println(thread);

        //得到connection
        Connection connection = DBUtil.getConnection();
        System.out.println(connection);

        System.out.println("User Dao insert");
    }
}

MyThreadLocal

package com.powernode.threadlocal;

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

//这个类负责使用map集合存储connection对象  72
public class MyThreadLocal {
    //所有需要和当前线程绑定的数据要放到这个容器中
    private Map map = new HashMap<>();

    //向ThreadLocal中绑定数据
    public void set(T obj){
        map.put(Thread.currentThread(),obj);
    }

    //从ThreadLocal中获取数据
    public T get(){
        return map.get(Thread.currentThread());
    }

    //移除ThreadLocal当中的数据
    public void remove(){
        map.remove(Thread.currentThread());
    }


}

Connection

package com.powernode.threadlocal;

//connection类  72
public class Connection {
}

DBUtil

package com.powernode.threadlocal;

//工具类  72
public class DBUtil {
    //静态变量特点，类加载时执行，并且只执行一次
    //全局大Map集合
    private  static MyThreadLocal local = new MyThreadLocal<>();

    //每次都调用这个方法来获取Connection对象
    public static Connection getConnection(){
        Connection connection = local.get();
        if(connection==null){
            //第一次调用getConnection方法的时候，connectin一定是空的
            //空的就new一次
            connection = new Connection();
            //将new的connection对象绑定到Map集合中
            local.set(connection);
        }
        return connection;
    }
}