数据库连接池

Posted 2021-03-22 laurarararararara

数据库连接池的目的：

减少频繁的创建/销毁连接，因为一次数据库连接的开销是很大的，要经过一下几个步骤：

1.加载驱动

2.获得一个Connection

3.通过TCP连接数据库

4.发送sql语句

5.执行sql，返回结果

6.关闭TCP连接

7.释放Connection

 

JDBC连接池测试数据库的连接：

import java.sql.*;

public class JDBCDemo {
    public static void main(String[] args) {
        //加载数据库的驱动 mysql: com.mysql.jdbc.Driver
        try {
            Class.forName("com.mysql.jdbc.Driver");
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }

        /**
         * 获取数据库的连接 DriverManager
         * URL格式:
         * jdbc:数据库子协议（mysql/oracle/sql sever）  ://ip:port/database_name
         * 数据库的连接URL：   jdbc:mysql://localhost:3306/exercise    exercise 是库名  3306数据库端口号
         *
         * 用户名：root
         * 密码：123456
         */
        //获取数据库的连接 DriverManager
        try {
            /**
             * getConnection源码
             * * @param   url a database url of the form
             *  * @return a connection to the URL
             *  返回一个URL
             *  所以必须捕获异常，防止url为空
             *  * @exception SQLException if a database access error occurs or the url is
             *      * {@code null}
             *      * @throws SQLTimeoutException  when the driver has determined that the
             *      * timeout value specified by the {@code setLoginTimeout} method
             *      * has been exceeded and has at least tried to cancel the
             *      * current database connection attempt
             */
            Connection connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/exercise", "root", "123456");



            //获取Statement的实例：通过connect实例获取
            /**
             * createStatement
             *  Creates a <code>Statement</code> object for sending SQL statements to the database.
             *      把sql语句给数据库
             */
            Statement statement = connection.createStatement();
            /**
             * 执行SQL：1.创建基本的statement对象
             * Statement statement = connection.createStatement();
             */

             //执行SQL
            String sql = "select * from student";

            //将SQL提交给MySQL数据库
          
            /**
             * executeQuery
             * * Executes the given SQL statement, which returns a single  <code>ResultSet</code> object.
             *  执行sql语句
             */
            ResultSet resultSet = statement.executeQuery(sql);


            //对结果集的处理
            System.out.println("SID:Sname:Ssex:Sage");
            while (resultSet.next()) {
                //boolean next() 判断返回结果集中是否还有数据
                //指定属性名
                String sid = resultSet.getString("SID");
                String sname = resultSet.getString("Sname");
                String ssex = resultSet.getString("Ssex");
                String sage = resultSet.getString("Sage");
                System.out.println(sid+":"+sname+":"+ssex+":"+sage);
            }

            //关闭资源
            statement.close();
            connection.close();
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}