程序博客网 > 网络突然连接不上

从最初的状态 一步一步重构出dao模式

来源：互联网 发布：网络突然连接不上 编辑：程序博客网 时间：2024/05/22 15:50

http://www.mldn.cn/articleview/2008-6-23/article_view_3195.htm 

 

一、前言
    本文的目的是将一个获取数据库连接的普通类重构成DAO+Abstract Factory模式。
    二、设计初衷
    使用数据访问对象（DAO，Data Access Object）模式来抽象和封装所有对数据源的访问。DAO管理着与数据源的连接以便检索和存储数据。可以降低商业逻辑层和数据访问层的耦合度，提高应用的可维护性和可移植性。
    由于底层数据源实现变化时，DAO向客户端提供的接口不会变化，所有该模式允许DAO调整到不同的存储模式，而不会影响其客户端或者业务组件。显然，DAO充当了组件和数据源之间的适配器。
    三、重构
    首先，创建一个获取数据库连接的普通类：
    DAOClient.java
    import java.sql.*;
    publicclass DAOClient {
        publicstaticvoid main( String[] args ) {
           try {
               //For Oracle
               Class.forName( "oracle.jdbc.driver.OracleDriver" );
               Connection conn = DriverManager.getConnection(
                      "jdbc:oracle:thin:@localhost:1521:dy", "scott", "tiger" );
               System.out.println( conn.toString() );
           } catch ( ClassNotFoundException e ) {
               e.printStackTrace();
           } catch ( SQLException e ) {
               e.printStackTrace();
           }
        }
    }

    再将这段代码封装到一个getConnection()方法中以便其它的地方调用：
    import java.sql.*;
    publicclass DAOClient {
        publicstaticvoid main( String[] args ) {
           Connection conn = getConnection();
           System.out.println( conn.toString() );
        }
        /**
         *得到一个Connection对象
         *@returnjava.sql.Connection
         */
        privatestatic Connection getConnection() {
           Connection conn = null;
           try {
               //For Oracle
               Class.forName( "oracle.jdbc.driver.OracleDriver" );
               conn = DriverManager.getConnection(
                      "jdbc:oracle:thin:@localhost:1521:dy", "scott", "tiger" );
           } catch ( ClassNotFoundException e ) {
               e.printStackTrace();
           } catch ( SQLException e ) {
               e.printStackTrace();
           }
           return conn;
        }
    }

    再将此方法定义到针对Oracle的工厂类中：
    OracleDAOFactory.java
    import java.sql.*;
    publicclass OracleDAOFactory {
        private OracleDAOFactory() {}
        /**
         *返回一个OracleDAOFactory对象
         *@returnOracleDAOFactory类型对象
         */
        publicstatic OracleDAOFactory newInstance() {
           returnnew OracleDAOFactory();
        }
        /**
         *得到一个Connection对象
         *@returnjava.sql.Connection
         */
        public Connection getConnection() {
           Connection conn = null;
           try {
               //For Oracle
               Class.forName( "oracle.jdbc.driver.OracleDriver" );
               conn = DriverManager.getConnection(
                      "jdbc:oracle:thin:@localhost:1521:dy", "scott", "tiger" );
           } catch ( ClassNotFoundException e ) {
               e.printStackTrace();
           } catch ( SQLException e ) {
               e.printStackTrace();
           }
           return conn;
        }
    }

    此时，DAOClient.java这个测试类的代码应修改为：
    import java.sql.*;
    public class DAOClient {
        publicstaticvoid main( String[] args ) {
           Connection conn = OracleDAOFactory.newInstance().getConnection();
           System.out.println( conn.toString() );
        }
    }

    考虑：通常，数据库服务器、数据库名、数据库用户、密码等应该从配置文件中获取。因此，修改Oracle的工厂类：
    import java.io.IOException;
    import java.sql.Connection;
    import java.sql.DriverManager;
    import java.sql.SQLException;
    import java.util.Properties;
    publicclass OracleDAOFactory {
        privatestatic Properties prop = new Properties();
        static {
           try {
               prop.load( OracleDAOFactory.class
                      .getResourceAsStream( "config.properties" ) );
           } catch ( IOException e ) {
               System.out.println( "File:config.properties no find,PLS check out!" );
               e.printStackTrace();
           }
        }
        private String CONNECTION_SERVER_NAME = prop
               .getProperty( "oracle_server_name" );
        private String CONNECTION_DRIVER = prop.getProperty( "oracle_conn_driver" );
        private String CONNECTION_DBINSTANCE = prop
               .getProperty( "oracle_dbInstance" );
        private String CONNECTION_USER = prop.getProperty( "oracle_conn_user" );
        private String CONNECTION_PWD = prop.getProperty( "oracle_conn_pwd" );
        private String CONNECTION_URL = "jdbc:oracle:thin:@"
               + CONNECTION_SERVER_NAME + ":1521:" + CONNECTION_DBINSTANCE;

       private OracleDAOFactory() {}
        /**
         *返回一个OracleDAOFactory对象
         *@returnOracleDAOFactory类型对象
         */
        publicstatic OracleDAOFactory newInstance() {
           returnnew OracleDAOFactory();
        }
        /**
         *得到一个Connection对象
         *@returnjava.sql.Connection
         */
        public Connection getConnection() {
           Connection conn = null;
           try {
               Class.forName( CONNECTION_DRIVER );
               conn = DriverManager.getConnection(
                      CONNECTION_URL, CONNECTION_USER, CONNECTION_PWD );
           } catch ( ClassNotFoundException e ) {
               e.printStackTrace();
           } catch ( SQLException e ) {
               e.printStackTrace();
           }
           return conn;
        }
    }

    添加配置文件config.properties：
    oracle_server_name=localhost
    oracle_conn_driver=oracle.jdbc.driver.OracleDriver
    oracle_dbInstance=dy
    oracle_conn_user=scott
    oracle_conn_pwd=tiger

    继续考虑，客户端在获取数据库连接时使用的是针对Oracle的数据库的工厂，但如果数据库变化了，那么客户端的代码还是要改变。因此，可以定义一个DAOFactory类，定义了一个抽象方法：getConnection()用于获取数据库连接，还有一个getDAOFactory()方法，根据参数dbType的值，返回不同的DAOFactory。
    DAOFactory.java
    import java.sql.Connection;
    publicabstractclass DAOFactory {
        publicstaticfinalintORACLE = 1;
        publicstaticfinalintSQLSERVER = 2;
        publicstaticfinalintMYSQL = 3;

        public abstract Connection getConnection();

        publicstatic DAOFactory getDAOFactory( int dbType ) {
           switch( dbType ) {
           caseORACLE:
               return OracleDAOFactory.newInstance();
           caseSQLSERVER:
               return SqlDAOFactory.newInstance();
           caseMYSQL:
               return MySqlDAOFactory.newInstance();
           default:
               returnnull;
           }
        }
    }

    SqlDAOFactory.java
    import java.io.IOException;
    import java.sql.Connection;
    import java.sql.DriverManager;
    import java.sql.SQLException;
    import java.util.Properties;
    publicclass SqlDAOFactory extends DAOFactory {
        privatestatic Properties prop = new Properties();
        static {
           try {
               prop.load( OracleDAOFactory.class
                      .getResourceAsStream( "config.properties" ) );
           } catch ( IOException e ) {
               System.out.println( "File:config.properties no find,PLS check out!" );
               e.printStackTrace();
           }
        }
        private String CONNECTION_SERVER_NAME = prop
               .getProperty( "sqlserver_server_name" );
        private String CONNECTION_DRIVER = prop.getProperty( "sqlserver_conn_driver" );
        private String CONNECTION_DBINSTANCE = prop
               .getProperty( "sqlserver_dbInstance" );
        private String CONNECTION_USER = prop.getProperty( "sqlserver_conn_user" );
        private String CONNECTION_PWD = prop.getProperty( "sqlserver_conn_pwd" );
        private String CONNECTION_URL = "jdbc:microsoft:sqlserver://"
               + CONNECTION_SERVER_NAME + ":1433;DatabaseName="
               + CONNECTION_DBINSTANCE;

        private SqlDAOFactory() {}
        /**
         *返回一个SqlDAOFactory对象
         *@returnSqlDAOFactory类型对象
         */
        publicstatic SqlDAOFactory newInstance() {
           returnnew SqlDAOFactory();
        }
        /**
         *得到一个Connection对象
         *@returnjava.sql.Connection
         */
        public Connection getConnection() {
           Connection conn = null;
           try {
               Class.forName( CONNECTION_DRIVER );
               conn = DriverManager.getConnection(
                      CONNECTION_URL, CONNECTION_USER, CONNECTION_PWD );
           } catch ( ClassNotFoundException e ) {
               e.printStackTrace();
           } catch ( SQLException e ) {
               e.printStackTrace();
           }
           return conn;
        }
    }

    MySqlDAPFactory.java
    import java.io.IOException;
    import java.sql.Connection;
    import java.sql.DriverManager;
    import java.sql.SQLException;
    import java.util.Properties;
    publicclass MySqlDAOFactory extends DAOFactory {
        privatestatic Properties prop = new Properties();
        static {
           try {
               prop.load( OracleDAOFactory.class
                      .getResourceAsStream( "config.properties" ) );
           } catch ( IOException e ) {
               System.out.println( "File:config.properties no find,PLS check out!" );
               e.printStackTrace();
           }
        }
        private String CONNECTION_SERVER_NAME = prop
               .getProperty( "mysql_server_name" );
        private String CONNECTION_DRIVER = prop.getProperty( "mysql_conn_driver" );
        private String CONNECTION_DBINSTANCE = prop
               .getProperty( "mysql_dbInstance" );
        private String CONNECTION_USER = prop.getProperty( "mysql_conn_user" );
        private String CONNECTION_PWD = prop.getProperty( "mysql_conn_pwd" );
        private String CONNECTION_URL = "jdbc:mysql://"
               + CONNECTION_SERVER_NAME + ":3306/" + CONNECTION_DBINSTANCE
               + "?useUnicode=true&characterEncoding=UTF-8";

        private MySqlDAOFactory() {}
        /**
         *返回一个MySqlDAOFactory对象
         *@returnMySqlDAOFactory类型对象
         */
        publicstatic MySqlDAOFactory newInstance() {
           returnnew MySqlDAOFactory();
        }
        /**
         *得到一个Connection对象
         *@returnjava.sql.Connection
         */

       public Connection getConnection() {
           Connection conn = null;
           try {
               Class.forName( CONNECTION_DRIVER );
               conn = DriverManager.getConnection(
                      CONNECTION_URL, CONNECTION_USER, CONNECTION_PWD );
           } catch ( ClassNotFoundException e ) {
               e.printStackTrace();
           } catch ( SQLException e ) {
               e.printStackTrace();
           }
           return conn;
        }
    }

    修改config.properties配置文件：
    #Oracle
    oracle_server_name=localhost
    oracle_conn_driver=oracle.jdbc.driver.OracleDriver
    oracle_dbInstance=dy
    oracle_conn_user=scott
    oracle_conn_pwd=tiger

    #SqlServer
    sqlserver_server_name=localhost
    sqlserver_conn_driver=com.microsoft.jdbc.sqlserver.SQLServerDriver
    sqlserver_dbInstance=test
    sqlserver_conn_user=sa
    sqlserver_conn_pwd=sa

    #MySql
    mysql_server_name=localhost
    mysql_conn_driver=com.mysql.jdbc.Driver
    mysql_dbInstance=test
    mysql_conn_user=root
    mysql_conn_pwd=root

    最后，修改客户端文件DAOClient.java代码：
    import java.sql.*;
    public class DAOClient {
        public static void main( String[] args ) {
           DAOFactory dao = DAOFactory.getDAOFactory( DAOFactory.ORACLE );
           Connection conn = dao.getConnection();
           System.out.println( conn.toString() );
        }
    }

    通过这种DAO+(Abstract)Factory方式，在将程序迁移到其它数据库中时，在客户端程序中几乎不用做修改，唯一需要做的，就是在获得DAOFactory对象的时候，修改相应的参数，例如，迁移到MySql下的时候：
    DAOFactory dao = DAOFactory.getDAOFactory( DAOFactory.MYSQL );

网络突然连接不上 网络突然连接不上
原创粉丝点击
热门IT博客
店铺精品数据采集神器店铺精品数据采集神器
以撒的结合mac破解版以撒的结合mac破解版
赌神风云软件
matlab 2014a mac
淘宝职业打假人黑名单
java错误需要标识符
nxpowerlite mac 破解
犀牛软件下载
阿里云用户中心在哪里
如何拼接json字符串
java抓包工具有哪些
网页源代码提取数据库
淘宝支付第三方服务商
淘宝第二层级 访客数
360极速浏览器mac下载
管家婆数据备份与恢复
淘宝联盟生成淘口令
mac怎么恢复出厂设置
飞机模型制造软件
大数据与数据挖掘
热门问题 老师的惩罚 人脸识别 我在镇武司摸鱼那些年 重生之率土为王 我在大康的咸鱼生活 盘龙之生命进化 天生仙种 凡人之先天五行 春回大明朝 姑娘不必设防，我是瞎子 赵莉颖 赵丽影 zhaoliying 赵立颖 赵靓颖 赴丽颖 赵丽疑 赵丽疑图片 赵丽英 我乃全能大明星杨过 杨乃文 杨乃文资料 杨乃文经典歌曲 杨乃文好听歌 一个人杨乃文歌词 杨乃文事件始末 陈绮贞杨乃文 杨乃文证据歌词 杨乃文 明天 杨乃文 金曲奖 祝我幸福杨乃文 杨乃文 queen 杨乃文铃声 杨乃文为什么那么叼 杨乃文当年发生了什么 安义杨天酒店 杨之光字画价格 杨之华 杨之华的第三任丈夫 杨之楹的身高是多少 酬乐天杨州初逢席上见赠 杨九红 杨九郎 杨九郎老婆 杨九郎结婚照 杨九郎超话 杨九郎老婆照片 杨九郎照片 杨九郎家境 杨九郎图片 杨九郎结婚当天

程序博客网，程序员的互联网技术博客家园。csdn论坛精品 msdn技术资料都在这里