使用C3P0連線池所需要的jar包：
c3p0-0.9.1.2.jar
commons-dbcp-1.4.jar
commons-dbutils-1.4.jar
commons-pool-1.5.6.jar
mysql-connector-java-5.1.39-bin.jar
ojdbc6.jar

utils程式碼：

package util;

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

import javax.sql.DataSource;

import com.mchange.v2.c3p0.ComboPooledDataSource;

public class DataSourceUtils {

	private static DataSource dataSource = new ComboPooledDataSource("mysql");

	private static ThreadLocal<Connection> tl = new ThreadLocal<Connection>();

	// 直接可以獲取一個連線池
	public static DataSource getDataSource() {
		return dataSource;
	}
	
	public static Connection getConnection() throws SQLException{
		return dataSource.getConnection();
	}

	// 獲取連線物件
	public static Connection getCurrentConnection() throws SQLException {

		Connection con = tl.get();
		if (con == null) {
			con = dataSource.getConnection();
			tl.set(con);
		}
		return con;
	}

	// 開啟事務
	public static void startTransaction() throws SQLException {
		Connection con = getCurrentConnection();
		if (con != null) {
			con.setAutoCommit(false);
		}
	}

	// 事務回滾
	public static void rollback() throws SQLException {
		Connection con = getCurrentConnection();
		if (con != null) {
			con.rollback();
		}
	}

	// 提交併且 關閉資源及從ThreadLocall中釋放
	public static void commitAndRelease() throws SQLException {
		Connection con = getCurrentConnection();
		if (con != null) {
			con.commit(); // 事務提交
			con.close();// 關閉資源
			tl.remove();// 從執行緒繫結中移除
		}
	}
	// 關閉資源方法
	public static void closeConnection() throws SQLException {
		Connection con = getCurrentConnection();
		if (con != null) {
			con.close();
		}
	}
	public static void closeStatement(Statement st) throws SQLException {
		if (st != null) {
			st.close();
		}
	}
	public static void closeResultSet(ResultSet rs) throws SQLException {
		if (rs != null) {
			rs.close();
		}
	}
}

 

書寫c3p0-config.xml檔案

<?xml version="1.0" encoding="UTF-8"?>
<c3p0-config>
	<default-config>
		<property name="driverClass">com.mysql.jdbc.Driver</property>
		<property name="jdbcUrl">jdbc:mysql://127.0.0.1:3306/learnj2ee?useSSL=false</property>
		<property name="user">root</property>
		<property name="password">123456</property>
		<property name="initialPoolSize">5</property>
		<property name="maxPoolSize">20</property>
	</default-config>

	<named-config name="oracle">
		<property name="driverClass">oracle.jdbc.OracleDriver</property>
		<property name="jdbcUrl">jdbc:oracle:thin:@10.10.130.115:1521:tgood</property>
		<property name="user">infodba</property>
		<property name="password">infodba</property>
	</named-config>
	
	<named-config name="mysql">
		<property name="driverClass">com.mysql.jdbc.Driver</property>
		<property name="jdbcUrl">jdbc:mysql://127.0.0.1:3306/shop?useSSL=false</property>
		<property name="user">root</property>
		<property name="password">123456</property>
		<property name="initialPoolSize">5</property>
		<property name="maxPoolSize">20</property>
	</named-config>
</c3p0-config>