C3P0连接池使用小结

C3P0在最近的demo中也用了（我用的是0.9.2.1版本），因为单例很难应付大量并发。

【引用请注明出处http://blog.csdn.net/bhq2010/article/details/9219947】

用法详见文档：http://www.mchange.com/projects/c3p0/

基本的用法在http://www.mchange.com/projects/c3p0/#quickstart，以及http://www.mchange.com/projects/c3p0/#using_c3p0中。

在项目中更为方便的做法是将配置写在配置文件中。

C0P0的配置文件名为c3p0-config.xml，详见http://www.mchange.com/projects/c3p0/#configuration_files

一个示例的配置文件如下：

【引用请注明出处http://blog.csdn.net/bhq2010/article/details/9219947】

<?xml version="1.0" encoding="UTF-8"?>

<c3p0-config>
	<default-config>
		<property name="automaticTestTable">t_c3p0_test</property>
		<property name="checkoutTimeout">10000</property>
		<property name="idleConnectionTestPeriod">10</property>
		<property name="initialPoolSize">5</property>
		<property name="maxIdleTime">600</property>
		<property name="maxPoolSize">20</property>
		<property name="minPoolSize">2</property>
		<property name="maxStatements">60</property>
		<property name="maxStatementsPerConnection">3</property>

		<user-overrides user="test-user">
			<property name="maxPoolSize">10</property>
			<property name="minPoolSize">1</property>
			<property name="maxStatements">0</property>
		</user-overrides>

	</default-config>

	<named-config name="metkb">
		<property name="acquireIncrement">20</property>
		<property name="initialPoolSize">10</property>
		<property name="minPoolSize">10</property>
		<property name="maxPoolSize">100</property>

		<property name="maxStatements">0</property>
		<property name="maxStatementsPerConnection">10</property>

		<!-- he's important, but there's only one of him -->
		<user-overrides user="master-of-the-universe">
			<property name="acquireIncrement">1</property>
			<property name="initialPoolSize">1</property>
			<property name="minPoolSize">1</property>
			<property name="maxPoolSize">5</property>
			<property name="maxStatementsPerConnection">50</property>
		</user-overrides>
	</named-config>
</c3p0-config>

放在eclipse Web工程的src目录下即可（eclipse会将该目录下的配置文件复制到tomcat的webapps/XXX/WEB-INF/classes下）

一个C3P0的单例的示例代码如下（连接池的单例并不妨碍并发，因为从连接池中取连接并不费时，而且取出的连接是线程安全的）：

【引用请注明出处http://blog.csdn.net/bhq2010/article/details/9219947】

package cn.edu.ruc.metkb.util;

import java.beans.PropertyVetoException;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

import com.mchange.v2.c3p0.ComboPooledDataSource;

public class PooledDBA implements DBA
{
	private ComboPooledDataSource cpds = null;
	private static Log dblog = null;
	private static String DBClassName = null;
	private static String DBName = null;
	private static String DBUrl = null;
	private static String DBUser = null;
	private static String DBPassword = null;

	protected PooledDBA()
	{
		cpds = new ComboPooledDataSource("metkb");
		try
		{
			cpds.setDriverClass( DBClassName );
		}
		catch (PropertyVetoException e)
		{
			dblog.exception(e);
		}           
		cpds.setJdbcUrl( DBUrl + DBName);
		cpds.setUser(DBUser);                                  
		cpds.setPassword(DBPassword);
	}

	static
	{
		try
		{
			DBClassName = ConfigFactory.getInstance().get("db.classname");
			DBName = ConfigFactory.getInstance().get("db.name");
			DBUrl = ConfigFactory.getInstance().get("db.url");
			DBUser = ConfigFactory.getInstance().get("db.user");
			DBPassword = ConfigFactory.getInstance().get("db.password");
			dblog = LogFactory.getInstance().getLog("db");
		}
		catch (Exception e)
		{
			e.printStackTrace();
		}
	}

	@Override
	public synchronized Connection getConnection() throws SQLException, ClassNotFoundException, InterruptedException
	{
		return cpds.getConnection();
	}

	@Override
	public synchronized void close(Connection conn)
	{
		try
		{
			if (conn != null)
			{
				conn.close();
				conn = null;
			}
		}
		catch (SQLException e)
		{
			dblog.exception(e);
		}
	}
	
	@Override
	public synchronized void close(Statement stat)
	{
		try
		{
			if (stat != null)
			{
				stat.close();
				stat = null;
			}
		}
		catch (SQLException e)
		{
			dblog.exception(e);
		}
	}
	
	@Override
	public synchronized void close(ResultSet rest)
	{
		try
		{
			if (rest != null)
			{
				rest.close();
				rest = null;
			}
		}
		catch (SQLException e)
		{
			dblog.exception(e);
		}
	}
}

【引用请注明出处http://blog.csdn.net/bhq2010/article/details/9219947】