如何重构出DAO模式

    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
               Class.forName( "oracle.jdbc.driver.Driver" );
               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
        
         */
        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
         类型对象
         */
        publicstatic OracleDAOFactory newInstance() {
           returnnew OracleDAOFactory();
        }
        /**
         *得到一个Connection对象
        
         */
        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、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;

 

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