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();
}
}
}
}