ThreadLocal (thread-local variables)

First, the use of control transaction to complete business functions

      (1) ThreadLocal Introduction
      (2) ThreadLocal objects and methods
      (3) TestThreadLocal

Second, the test connector in obtaining two single-threaded connection

      (1) Test at JdbcUtil package
      (2) under test JdbcUtil2 package
      (3) given in the code package JdbcUtil2

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First, the use of control transaction to complete business functions

(1) ThreadLocal Introduction

• ThreadLocal function: to hold the same value for the same thread, hold different values ​​for different threads.
• Objective: In each piece of code in a thread, only one connection is connected

Want to get in a single-threaded programming connection, it should be to get a connection with, but before the hand tools JDBC package , there is no use ThreadLocal control transaction, each will create a new connection, so consumption is very large. ThreadLocal a good solution to this problem.

(2) ThreadLocal objects and methods

Create a ThreadLocal objects:ThreadLocal<T> tdl = new ThreadLocal<T>();

ThreadLocal Methods:

• set (T t); // Thread t is added to the current object.
• get (); // get the object of the current Thread.
• remove (); // remove the object in the current Thread.

(3)TestThreadLocal

package jdbc;

public class TestThreadLocal {
	public static void main(String[] args) throws Exception {
		//tl对象可以为同一个线程保存相同的值,为不同线程保存不同的值.
		final ThreadLocal<String> tl = new ThreadLocal<String>();
		Thread t1 = new Thread() {
			public void run() {
				tl.set("hello");
				System.out.println("t1:" + tl.get());
			}
		};
		t1.start();
		Thread.sleep(1000);
		
		Thread t2 = new Thread() {
			public void run() {
				tl.set("world");
				System.out.println("t2:"+tl.get());
			}
		};
		t2.start();
	}
}

Second, the test connector in obtaining two single-threaded connection

(1) Test packet at JdbcUtil

Conn found two different addresses, the instructions for creating the two connections.

(2) Test packet at JdbcUtil2

This can be seen with a conn objects, the task is completed.

(3) given in the code package JdbcUtil2

package util;

import java.io.IOException;
import java.io.InputStream;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.Properties;

/**
 * Jdbc工具类
 * 1:properties配置文件 封装获取连接 释放资源 提高代码复用性√
 * 2:类加载时加载驱动√
 * 3:ThreadLocal控制事务√
 * 4:连接池,提高资源利用率×
 * 5:rowmapper封装 减少代码冗余×
 * 6:template封装 减少dao层代码冗余×
 * @author 郭乾亮1998
 *
 */
public class JdbcUtil2 {
	//创建properties
	static Properties pro = new Properties();
	//创建ThreadLocal<Connection>,可以为同一个线程保存同一个连接,为不同线程保存不同的连接
	private static ThreadLocal<Connection> tl = new ThreadLocal<Connection>();
	
	//加载驱动
	static{
		InputStream is = null;
		try {
			is = JdbcUtil.class.getResourceAsStream("/conf/db.properties");
			//加载文件
			pro.load(is);
			Class.forName(pro.getProperty("driverClassName"));
		} catch (Exception e) {
			e.printStackTrace();
		}finally{
			try {
				is.close();
			} catch (IOException e) {
				e.printStackTrace();
			}
		}
	}
	//获取连接
	public static Connection getConnection() throws Exception{
		Connection conn = tl.get();//获得当前线程中的连接
		if(conn == null){//如果当前线程中没有连接
			String url = pro.getProperty("url");
			String user = pro.getProperty("username");
			String password = pro.getProperty("password");
			//创建连接
			conn = DriverManager.getConnection(url,user,password);
			//将连接保存到当前线程
			tl.set(conn);
		}
		return conn;
	}
	//释放资源
	public static void release(ResultSet rs,PreparedStatement pstm,Connection conn) throws Exception{
		if(rs!=null){
			rs.close();
		}
		if(pstm!=null){
			pstm.close();
		}
		if(conn!=null){
			conn.close();
			tl.remove();//将连接从当前线程中移除
		}
	}
}