利用工厂模式实现serviec层和dao层解耦

利用工厂模式实现serveice和dao层的解耦，这样就可以不用在service层实例化dao层的对象，当dao层代码发生改变的时候（数据库实现发生改变）直接修改配置文件就不用改变service层的代码。

配置文件：dao.properties

UserDao="com.dao.UserDaoJdbcImp" 如果是oracle实现就可以修改配置文件就行

　　

源代码：DaoFactory.java

 package com.demo;

 import java.io.IOException;

 import java.io.InputStream;

 import java.util.Properties;

 import org.hamcrest.Factory;

 //利用工厂模式实现业务层与DAO层解耦

 public class DaoFactory {

11     private static Properties daoConfig = new Properties();

     private  static DaoFactory factory = new DaoFactory();

     private DaoFactory(){

         //加载配置文件

15         InputStream in = DaoFactory.class.getClassLoader().getResourceAsStream("dao.properties");

         try {

             daoConfig.load(in);

         } catch (IOException e) {

             throw new RuntimeException();

         }

     }

     //获取工厂对象

     public static DaoFactory getInstance(){

         return factory;

     }

29     public static <T> T createDao(Class<T> clazz){//这里传进来的是DAO接口

30         String name = clazz.getSimpleName();//UserDao

31         String className = daoConfig.getProperty(name);

32         try {

33             T dao = (T) Class.forName(className).newInstance();

34             return dao;

35         } catch (Exception e) {

36              throw new RuntimeException(e);

37         }

38     }

 }