c3po简单了解

package com.hanchao.test;import java.lang.reflect.Field;import java.sql.Connection;import java.sql.ResultSet;import java.sql.SQLException;import java.sql.Statement;import java.util.Scanner;import javax.sql.DataSource;import com.mchange.v2.c3p0.DataSources;/*********************** * @author：han     * @version：1.0         * @created：2015-10-11     *********************** */public class TestPool {                public static void main(String[] args) {                /*              Scanner input = new Scanner(System.in);                System.out.println("请输入账号:");                String name = input.next();                System.out.println("请输入密码:");                String pwd = input.next();                System.out.println("请输入金额:");                float money = input.nextFloat();*/                                final String DRIVER = "com.mysql.jdbc.Driver";                //final String URL = "jdbc:mysql://127.0.0.1:3306/mydb";                //final String URL = "jdbc:mysql://localhost:3306/mydb";                final String URL = "jdbc:mysql:///mydb";                final String NAME = "root";                final String PASSWORD = "root";                                Connection conn = null;                Statement stat = null;                ResultSet rs = null;                                try {                        //1.加载数据库驱动                        Class.forName(DRIVER);                        //连接mysql数据库                        DataSource unpooled = DataSources.unpooledDataSource(URL,NAME,PASSWORD);                        //构建一个连接池                        DataSource pooled = DataSources.pooledDataSource(unpooled);                        //2.获取数据库连接(first Time)                    conn = pooled.getConnection();                        System.out.println("1 con Class Type is :" + conn.getClass().getName());                        //取得内部的实际数据库连接                        Object o1 = getInner(conn);                        System.out.println("1 Inner con Class Type is :" + o1.getClass().getName());                                                //3.获取Statement对象                        stat = conn.createStatement();                        //4.执行SQL                        rs = stat.executeQuery(" select * from t_user where id = 13");                    while (rs.next()) {                                System.out.println(" username:" + rs.getString("username"));                        }                                        //5.关闭连接                    rs.close();                    stat.close();                    conn.close();                                        //6.等待连接返回池中                    try {                                Thread.sleep(1000);                        } catch (InterruptedException e) {                                e.printStackTrace();                        }                                        //第二次获取数据库连接                    conn = pooled.getConnection();                        System.out.println("2 con Class Type is :" + conn.getClass().getName());                        Object o2 = getInner(conn);                        System.out.println("2 Inner con Class Type is :" + o2.getClass().getName());                                                //获取Statement对象                        stat = conn.createStatement();                                                //3.获取Statement对象                        stat = conn.createStatement();                        //4.执行SQL                        rs = stat.executeQuery(" select * from t_user where id = 13");                    while (rs.next()) {                                System.out.println(" username:" + rs.getString("username"));                        }/*                        //3.获取Statement对象//                      String sql = "delete from t_user where id = 13";//                      String sql = "insert into t_user(username,address) values('tom1','USA1')";                    StringBuilder sql = new StringBuilder();                    sql.append("INSERT INTO t_account(username,`password`,money,`enable`)  ");                    sql.append("VALUES ");                    sql.append("('"+name+"','"+pwd+"','"+money+"','1')");                                        System.out.println("SQL:" + sql.toString());                                                //执行SQL//                      int rows = stat.executeUpdate(sql);                        int rows = stat.executeUpdate(sql.toString());                        if (rows > 0) {                                System.out.println("execute OK!!");                        } else {                                System.out.println("execute error !!");                        }                                        */                      } catch (ClassNotFoundException e) {                        e.printStackTrace();                } catch (SQLException e) {                        e.printStackTrace();                } finally {                        try {                                if (stat != null) {                                        stat.close();                                }                        } catch (SQLException e) {                                e.printStackTrace();                        } finally {                                try {                                        if (conn != null) {                                                conn.close();                                        }                                } catch (SQLException e) {                                        e.printStackTrace();                                }                        }                }        }        private static Object getInner(Object conn) {                Object object = null;                Field f ;                                try {                        f = conn.getClass().getDeclaredField("inner");                        f.setAccessible(true);                        object = f.get(conn);                        f.setAccessible(false);                } catch (Exception e) {                        e.printStackTrace();                }                 return object;        }}

结果：

首先，从数据库连接池获得一个连接。发现连接类型并不是mysql的数据库连接，而是，com.mchange.v2.c3p0.impl.NewProxyConnection。通过类名，可以推测，从数据库连接池中获取的只是一个代理。

当我们关闭.NewProxyConnection连接时，并没有真正关闭连接，而只是将数据库连接放入连接池保存，使得数据库连接在连接池中得到复用。而从连接池返回的NewProxyConnection对象，只是对真实数据库连接的包装。