需要准备的jar包：

MySQL的jar包mysql-connector-java-5.1.39-bin目前是5.1.39版本：
http://dev.mysql.com/downloads/connector/j/

C3p0的2个包：
https://sourceforge.net/projects/c3p0/
c3p0-0.9.1.2.jar和c3p0-sources-0.9.1.2.jar

配置文件：c3p0-config.xml
名字必须为这个！

<c3p0-config>
    <!-- 默认配置，如果没有指定则使用这个配置 -->
    <default-config>
        <property name="driverClass">com.mysql.jdbc.Driver</property>
        <property name="jdbcUrl">
            <![CDATA[jdbc:mysql://127.0.0.1:3306/hncu?useUnicode=true&characterEncoding=UTF-8]]>
        </property>
        <property name="user">root</property>
        <property name="password">1234</property>
        <!-- 初始化池大小 -->
        <property name="initialPoolSize">2</property>
        <!-- 最大空闲时间 -->
        <property name="maxIdleTime">30</property>
        <!-- 最多有多少个连接 -->
        <property name="maxPoolSize">10</property>
        <!-- 最少几个连接 -->
        <property name="minPoolSize">2</property>
        <!-- 每次最多可以执行多少个批处理语句 -->
        <property name="maxStatements">50</property>
    </default-config> 
    <!-- 命名的配置 -->
    <named-config name="demo">
        <property name="driverClass">com.mysql.jdbc.Driver</property>
        <property name="jdbcUrl"><![CDATA[jdbc:mysql://127.0.0.1:3306/hncu?useUnicode=true&characterEncoding=UTF-8]]></property>
        <property name="user">root</property>
        <property name="password">1234</property>
        <property name="acquireIncrement">5</property><!-- 如果池中数据连接不够时一次增长多少个 -->
        <property name="initialPoolSize">100</property>
        <property name="minPoolSize">50</property>
        <property name="maxPoolSize">1000</property>
        <property name="maxStatements">0</property>
        <property name="maxStatementsPerConnection">5</property> <!-- he's important, but there's only one of him -->
    </named-config>
</c3p0-config> 

演示代码：

package cn.hncu.C3p0;

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

import org.junit.Test;

import com.mchange.v2.c3p0.ComboPooledDataSource;

public class C3p0Demo {

    @Test
    // 纯Java方法使用c3p0
    public void C3p0Demo() throws PropertyVetoException, SQLException {
        ComboPooledDataSource pool = new ComboPooledDataSource();
        pool.setUser("root");// 用户姓名
        pool.setPassword("1234");// 用户密码
        pool.setJdbcUrl("jdbc:mysql://127.0.0.1:3306/hncu?useUnicode=true&characterEncoding=utf-8");// MySQL数据库连接url
        pool.setDriverClass("com.mysql.jdbc.Driver");

        // pool可以调用set方法进行Connection池的配置

        // 连接关闭之后，内存会被释放，下次取时会重新开(内存地址不共用)
        for (int i = 0; i < 20; i++) {
            Connection con = pool.getConnection();
            System.out.println(i + ":" + con);
            if (i % 2 == 0) {
                con.close();
            }
        }
    }

    @Test
    // 演示采用配置文件的方式使用c3p0
    public void C3p0PropertyDemo() throws SQLException {
        ComboPooledDataSource pool = new ComboPooledDataSource();//空参，自动到classpath目录下面加载“c3p0-config.xml”配置文件---配置文件的存储位置和名称必须是这样，且使用“默认配置”
        //ComboPooledDataSource pool = new ComboPooledDataSource("demo");//加载“c3p0-config.xml”文件中定义的“demo”这个配置元素
         for(int i=0;i<25;i++){
               Connection con = pool.getConnection();
               System.out.println(i+":"+ con.hashCode());
           }
    }

}

包装一下C3P0的Connection池

package cn.hncu.C3p0;

import java.sql.Connection;
import java.sql.SQLException;

import javax.sql.DataSource;

import com.mchange.v2.c3p0.ComboPooledDataSource;

public class C3p0Pool {
    //我们的这个包装，只是为了把c3p0池做成让每个线程(客户端)获得的是同一个连接，方便做b/s框架下的事务
    private static DataSource pool;
    private static ThreadLocal<Connection> t = new ThreadLocal<Connection>();
    static{
        pool = new ComboPooledDataSource("demo");
        //这里的参数视你的配置文件而定，也可以不写，用默认的配置
    }

    public static DataSource getDataSource(){
        return pool;
    }

    public static Connection getConnection() throws SQLException{
        Connection con = t.get();
        if(con==null){
            con=pool.getConnection();
            t.set(con);
        }
        return con;
    }
}

转载请附上原文博客链接：
http://blog.csdn.net/qq_26525215