spring di(即依赖注入)的原理个人理解是这样子的，先读取配置文件，在通过解析xml将有用的信息扣取出来，再通过反射机制来实现类或方法的实例化。
今天我模拟了两种注入方式一种是注入bean，另一种是注入一个factory.对于工厂模式本人觉得还蛮好用的，只要搭建起了架构感觉管理起来挺容易的。还有bridge模式在开发中也是很便于管理的。所以我在这个小例子里面结合了bridge和factory模式。

下面是代码：
1，UserDao:接口

public interface UserDao { public boolean add(); }

2，ImplUserDaoMySql：实现UserDao接口的MySql数据库dao层

public class ImplUserDaoMySql implements UserDao { @Override public boolean add() { System.out.println("add MySql Dao!"); return true; } }

3，ImplUserDaoOracle：实现UserDao接口的Oracle数据库dao层

public class ImplUserDaoOracle implements UserDao { @Override public boolean add() { System.out.println("add Oracle Dao!"); return true; } }

上面两个就可以体现出桥模式的优点

4，DaoFactory：工厂模式类用于生产各种UserDao

public class DaoFactory { public static UserDao getUserDaoOracle(){ return new ImplUserDaoOracle(); } public static UserDao getUserDaoMySql(){ return new ImplUserDaoMySql(); } }

5，AnalogApplicationContext：模拟di主程序

public class AnalogApplicationContext { private Map<String, Object> map = new HashMap<String, Object>(); public AnalogApplicationContext(String configLocation) { // 解析配置文件，将信息放入map中 SAXReader sax = new SAXReader(); try { Document document = sax.read(AnalogApplicationContext.class .getResourceAsStream(configLocation)); Element root = document.getRootElement(); List<Element> elements = root.elements(); for (int i = 0; i < elements.size(); i++) { Element element = elements.get(i); String idDI = element.attribute("id").getData().toString(); String classDI = element.attribute("class").getData() .toString(); String factoryMethodDI = ""; if (element.attribute("factory-method") == null) { map.put(idDI, Class.forName(classDI).newInstance()); } else { factoryMethodDI = element.attribute("factory-method") .getData().toString(); Object obj = Class.forName(classDI).newInstance() .getClass().getDeclaredMethod(factoryMethodDI) .invoke(Class.forName(classDI).newInstance()); map.put(idDI, obj); } } } catch (Exception e) { e.printStackTrace(); } } public Object getBean(String id) { return map.get(id); } }

6，applicationContext-di.xml：spring模拟配置文件，注意本模拟程序中applicationContext-di.xml必须和AnalogApplicationContext.java主模拟程序放在同一目录下，应为我获取applicationContext-di.xml文件路径是先通过AnalogApplicationContext.java来获取，当然这个也是可变的，自由发挥喽。

<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:aop="http://www.springframework.org/schema/aop" xmlns:tx="http://www.springframework.org/schema/tx" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.0.xsd http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-2.0.xsd http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-2.0.xsd"> <bean id="userDaoOracle" class="com.fairy.spring.di.impldao.ImplUserDaoOracle" /> <bean id="userDaoMySql" class="com.fairy.spring.di.daofactory.DaoFactory" factory-method="getUserDaoMySql" /> </beans>

7，TestDI：测试类，用来测试两种注入方式

public class TestDI { /** * @测试模拟spring DI程序 */ public static void main(String[] args) { /** * 测试bean注入模式 */ AnalogApplicationContext alAcOracle = new AnalogApplicationContext("applicationContext-di.xml"); UserDao userdaoOracle = (UserDao)alAcOracle.getBean("userDaoOracle"); userdaoOracle.add(); /** * 测试factory注入模式 */ AnalogApplicationContext alAcMySql = new AnalogApplicationContext("applicationContext-di.xml"); UserDao userdaoMySql = (UserDao)alAcMySql.getBean("userDaoMySql"); userdaoMySql.add(); } }