以前认为连接池，线程池这些东西很高端。因为出了问题之后，总是有人说这个连接池/线程线的配置不对嘛，应该..... 今天学习了下，这个池到底应该怎么设计。发现apache的common-pool早就思考过这个问题了，并且定义了一个规范和框架。基于此我学习了些资料来写一个数据库连接池。

先写个测试程序，多线程不停的拿连接与释放连接，取到连接就打印一下连接id。如果同一个id，出现多次，则证明这个连接被复用了。

1.测试程序

public class TestJDBCPool {

public static void main(String[] args) {

//初始化,实际可用spring初始化

JDBCPool pool=new JDBCPool("jdbc:mysql://localhost:3306/test","root","xx","com.mysql.jdbc.Driver",null);

try {

for (int i = 0; i < 200; i++) {

new Thread(new PoolTestThread(pool)).start();

}

} catch (Exception e) {

e.printStackTrace();

}

}

private static class PoolTestThread implements Runnable {

private JDBCPool pool;

public PoolTestThread(JDBCPool pool) {

this.pool=pool;

}

public void run() {

try {

Connection conn = pool.getConnection();

System.out.println(Thread.currentThread().getName() + " : " + conn.hashCode());

Thread.sleep(1000);

//归还连接

JDBCPool.returnConnection(conn);

} catch (Exception e) {

// TODO Auto-generated catch block

e.printStackTrace();

}

}

}

}

2.设计JDBCPool

根据common-pool的定义，我们要定义两个类，一个是Pool类给应用提供"取对象"与"还对象"两个方法。另一个是PooledObjectFactory类，用于生产对象与包装对象。

package net.highersoft.pool;

import java.sql.Connection;

import java.sql.DriverManager;

import org.apache.commons.pool2.BasePooledObjectFactory;

import org.apache.commons.pool2.PooledObject;

import org.apache.commons.pool2.impl.DefaultPooledObject;

import org.apache.commons.pool2.impl.GenericObjectPool;

import org.apache.commons.pool2.impl.GenericObjectPoolConfig;

public class JDBCPool {

private volatile static JDBCPool pool;

private static GenericObjectPool connPool;

/**

* 初始化连接池，传递所需资源

* @param url

* @param userName

* @param passwd

* @param driver

* @param config

*/

public JDBCPool(String url,String userName,String passwd,String driver,GenericObjectPoolConfig config) {

if (config == null) {

config = getDefaultConfig();

}

connPool = new GenericObjectPool(new JDBCPooledFactory(url,userName,passwd,driver), config);

}

private GenericObjectPoolConfig getDefaultConfig() {

GenericObjectPoolConfig conf = new GenericObjectPoolConfig();

// TODO -- 默认8,8,0

conf.setMaxTotal(50);

conf.setMaxIdle(50);

conf.setMinIdle(0);

conf.setMaxWaitMillis(60000);

return conf;

}

/**

* 得到连接

* @return

* @throws Exception

*/

public Connection getConnection() throws Exception {

return connPool.borrowObject();

}

/**

* 释放连接

* @param conn

*/

public static void returnConnection(Connection conn) {

connPool.returnObject(conn);

}

static class JDBCPooledFactory extends BasePooledObjectFactory {

private String url;

private String userName;

private String passwd;

public JDBCPooledFactory(String url,String userName,String passwd,String driver) {

try {

Class.forName(driver);

} catch (ClassNotFoundException e) {

e.printStackTrace();

}

this.url=url;

this.userName=userName;

this.passwd=passwd;

}

//创建对象

@Override

public Connection create() throws Exception {

return DriverManager.getConnection(url, userName, passwd);

}

//包装对象

@Override

public PooledObject wrap(Connection conn) {

return new DefaultPooledObject(conn);

}

}

}

再看一下maven依赖:

org.apache.commons

commons-pool2

2.4.2

mysql

mysql-connector-java

5.0.5