mysql使用连接池的示例：

1.手动配置连接池。

/**
     * 手动设置连接池
     */
    public void demo1(){
        // 获得连接:
        Connection conn = null;
        PreparedStatement pstmt = null;
        ResultSet rs = null;
        try{
            // 创建连接池:
            ComboPooledDataSource dataSource = new ComboPooledDataSource();
            // 设置连接池的参数:
            dataSource.setDriverClass("com.mysql.jdbc.Driver");
            dataSource.setJdbcUrl("jdbc:mysql:///jdbctest");
            dataSource.setUser("root");
            dataSource.setPassword("abc");
            dataSource.setMaxPoolSize(20);
            dataSource.setInitialPoolSize(3);
            
            // 获得连接:
            conn = dataSource.getConnection();
            // 编写Sql:
            String sql = "select * from user";
            // 预编译SQL:
            pstmt = conn.prepareStatement(sql);
            // 设置参数
            // 执行SQL:
            rs = pstmt.executeQuery();
            while(rs.next()){
                System.out.println(rs.getInt("uid")+"   "+rs.getString("username")+"   "+rs.getString("password")+"   "+rs.getString("name"));
            }
        }catch(Exception e){
            e.printStackTrace();
        }finally{
            JDBCUtils.release(rs, pstmt, conn);
        }
    }

2.使用配置文件配置连接池，配置文件xml如下：

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

3.使用配置文件。

/**
     * 使用配置文件的方式
     */
    public void demo2(){
        Connection conn = null;
        PreparedStatement pstmt = null;
        ResultSet rs = null;
        try{
            /*// 获得连接:
            ComboPooledDataSource dataSource = new ComboPooledDataSource();*/
            // 获得连接:
            // conn = dataSource.getConnection();
            conn = JDBCUtils2.getConnection();
            // 编写Sql:
            String sql = "select * from user";
            // 预编译SQL:
            pstmt = conn.prepareStatement(sql);
            // 设置参数
            // 执行SQL:
            rs = pstmt.executeQuery();
            while(rs.next()){
                System.out.println(rs.getInt("uid")+"   "+rs.getString("username")+"   "+rs.getString("password")+"   "+rs.getString("name"));
            }
        }catch(Exception e){
            e.printStackTrace();
        }finally{
            JDBCUtils2.release(rs, pstmt, conn);
        }
    }