知识大全如何重构出DAO模式

Posted 2022-07-19 知

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　　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管理著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: :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: :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: :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 + : : + 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 = ; publicstaticfinalintSQLSERVER = ; publicstaticfinalintMYSQL = ;

　　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 + : ;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 + : / + CONNECTION_DBINSTANCE + ?useUnicode=true&characterEncoding=UTF ;

　　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= microsoft jdbc sqlserver SQLServerDriver sqlserver_dbInstance=test sqlserver_conn_user=sa sqlserver_conn_pwd=sa

　　#MySql mysql_server_name=localhost mysql_conn_driver= 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() );

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知识大全 如何重构出DAO模式

知识大全如何重构出DAO模式