并发示例——实现简易的数据库连接池

一、引言

在前一篇文章中线程间通信，介绍了线程间的通信。主要对实现该机制的两种方式：synchronized+wait-notify模式和 Lock+Condition 模式进行介绍。下面用上面的两种机制，实现简易的数据库连接池，加深理解。

二、数据库连接池，方式一

package com.scorpios.mybatis.thread;

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

public class MyDataSource {

	private LinkedList<Connection> pool = new LinkedList<>();// 用于存放数据库连接池

	private static final int INIT_CONNECTIONS = 10;// 连接池大小

	private static final String DRIVER_CLASS = "";

	private static final String USER = "";

	private static final String PASSWORD = "";

	private static final String URL = "";

	static {
		try {
			Class.forName(DRIVER_CLASS);// 模拟加载数据库驱动
		} catch (ClassNotFoundException e) {
			e.printStackTrace();
		}
	}

	public MyDataSource2() {
		// 循环创建10个连接池
		for (int i = 0; i < INIT_CONNECTIONS; i++) {
			try {
				Connection conn = DriverManager.getConnection(URL, USER, PASSWORD);
				// 加到队列中
				pool.addLast(conn);
			} catch (SQLException e) {
				e.printStackTrace();
			}
		}
	}

	// 从队列中获取连接
	public synchronized Connection getConnect() {
		Connection result = null;
		synchronized (pool) {
			// 如果连接池中没有连接，则要等待
			while (pool.size() <= 0) {// 这地方一定要用while，而不是if
				try {
					wait();
				} catch (InterruptedException e) {
					e.printStackTrace();
				}
			}
			// 连接池中有连接
			if (!pool.isEmpty()) {
				result = pool.removeFirst();
			}
			return result;
		}
	}

	// 释放连接，把连接放回到连接池中
	public synchronized void release(Connection conn) {
		if (conn != null) {
			synchronized (pool) {
				pool.addLast(conn);
				notifyAll();
			}
		}
	}

}

三、数据库连接池，方式二

package com.scorpios.mybatis.thread;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.LinkedList;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

public class MyDataSource2 {

	private LinkedList<Connection> pool = new LinkedList<>();// 用于存放数据库连接池

	private static final int INIT_CONNECTIONS = 10;// 连接池大小

	private static final String DRIVER_CLASS = "";

	private static final String USER = "";

	private static final String PASSWORD = "";

	private static final String URL = "";

	private Lock lock = new ReentrantLock(); // 获取Lock
	private Condition c1 = lock.newCondition();// 获得Condition

	static {
		try {
			Class.forName(DRIVER_CLASS);// 模拟加载数据库驱动
		} catch (ClassNotFoundException e) {
			e.printStackTrace();
		}
	}

	public MyDataSource() {
		// 循环创建10个连接池
		for (int i = 0; i < INIT_CONNECTIONS; i++) {
			try {
				Connection conn = DriverManager.getConnection(URL, USER, PASSWORD);
				// 加到队列中
				pool.addLast(conn);
			} catch (SQLException e) {
				e.printStackTrace();
			}
		}
	}

	// 从队列中获取连接
	public Connection getConnect() {
		Connection result = null;
		lock.lock();
		try {
			while (pool.size() <= 0) {
				try {
					c1.await();
				} catch (InterruptedException e) {
					e.printStackTrace();
				}
			}
			if (!pool.isEmpty()) {
				result = pool.removeFirst();
			}
			return result;
		} finally {
			lock.unlock();
		}
	}

	// 释放连接，把连接放回到连接池中
	public void release(Connection conn) {
		if (conn != null) {
			lock.lock();
			try {
				pool.addLast(conn);
				c1.signal();
			} finally {
				lock.unlock();
			}
		}
	}

}