七、ThreadLocal

例一：

public class ThreadLocalTest03 {    
    private static ThreadLocal<Integer> threadLocal = ThreadLocal.withInitial(()-> 1);
    public static void main(String[] args) {
        new Thread(new MyRun(),"a").start();
        new Thread(new MyRun(),"b").start();
    }    
    public static  class MyRun implements Runnable{
        public MyRun() {       //main
            threadLocal.set(-100);
            System.out.println(Thread.currentThread().getName()+"-->"+threadLocal.get());    
        }
        public void run() {
            System.out.println(Thread.currentThread().getName()+"-->"+threadLocal.get());    
            //new Thread(new MyRunxxx()).start();
        }
    }
    
}

例二：操作数据库

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;

public class DBUtil3 {
    private static final String DRIVER="com.mysql.jdbc.Driver";
    private static final String    USER="root";
    private static final String PWD="root";
    private static final String URL="jdbc:mysql://localhost:3306/test?useUnicode=true&characterEncoding=utf8";
    
    //定义一个数据库连接
    private static Connection conn=null;
    private static ThreadLocal<Connection> connContainer=new ThreadLocal<Connection>(){
        protected Connection initialValue() {
            try {
                Class.forName(DRIVER);
                
                if(conn==null){
                    
                    conn=DriverManager.getConnection(URL, USER, PWD);
                }
                
            } catch (ClassNotFoundException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } catch (SQLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } 
            return conn;
        };
    };
    //获取连接
    public   static Connection getConnection(){
        return connContainer.get(); //获取连接
        
    }
    //关闭连接的方法
    public   static void colseConnection(){
        if (conn!=null) {
            try {
                conn.close();
            
            } catch (SQLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            
        }
    }
    public static void main(String[] args) {
        System.out.println(getConnection());
    }
}

例二：