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     }
 }