当用户多的时候，每次打开关闭连接 会很耗资源和时间，所以连接池的作用就有了；
以C3P0连接池 为例: C3P0连接池 C3P0简介 C3P0也是开源免费的连接池，现在做的大部分项目都是使用C3P0连接池。 C3P0的使用 C3P0中池类是：ComboPooledDataSource。
简单的操作:
//导入C3P0jar包，新建一个DBUtils类，如下 import java.beans.PropertyVetoException; import java.sql.Connection; import java.sql.SQLException; import com.mchange.v2.c3p0.ComboPooledDataSource; public class DBUtils { public static Connection initConnection() { try { ComboPooledDataSource dataSource = new ComboPooledDataSource(); String url = "jdbc:mysql://localhost:3306/test"; dataSource.setJdbcUrl(url); dataSource.setUser("root"); dataSource.setPassword("root"); dataSource.setDriverClass("com.mysql.jdbc.Driver"); Connection connection = dataSource.getConnection(); return connection; } catch (PropertyVetoException e) { e.printStackTrace(); } catch (SQLException e) { // TODO Auto-generated catch block e.printStackTrace(); } return null; } }//然后 新建一个Main类
import java.sql.Connection; import java.sql.DriverManager; import java.sql.PreparedStatement; import java.sql.ResultSet; import java.sql.SQLException; public class Main { public static void main(String[] args) throws SQLException { String ClassName = "com.mysql.jdbc.Driver";//固定格式 String url = "jdbc:mysql://localhost:3306/test";//test是在mysql下自定义建立的数据库 String userName = "root";//mysql的user，就是你在安装mysql时设定的用户名，和下面的用户密码 同理 String password = "root"; Connection connect = null; PreparedStatement statement1 = null; try { Class.forName(ClassName); //connect = DriverManager.getConnection(url, userName, password); //改成从连接池中取返回的connection connect = DBUtils.initConnection(); System.out.println("Success connent the Mysql server"); String sql = "select * from user"; statement1 = connect.prepareStatement(sql); ResultSet rSet = statement1.executeQuery(); while ( rSet.next() ) { System.out.print(rSet.getString("name")); System.out.print(" "); System.out.println(rSet.getString("password")); } } catch (ClassNotFoundException e) { System.out.println("Error loading Mysql Driver"); e.printStackTrace(); } catch (SQLException e) { // TODO Auto-generated catch block e.printStackTrace(); } finally { //关闭流 statement1.close(); //关闭连接 connect.close(); } } }实现了如下结果:
