模拟实现Spring框架

Spring框架主要就是使用反射机制实现IOC/DI。

applicationContext.xml

<beans>
	<bean id="u" class="com.bjsxt.dao.impl.UserDAOImpl" />
	<bean id="userService" class="com.bjsxt.service.UserService" >
		<property name="userDAO" bean="u"/>
	</bean>
</beans>

BeanFactory.java

public interface BeanFactory {
	public Object getBean(String id);
}

ClassPathXmlApplicationContext.java

public class ClassPathXmlApplicationContext implements BeanFactory {
	
	private Map<String , Object> beans = new HashMap<String, Object>();
	
	public ClassPathXmlApplicationContext() throws Exception {
		SAXBuilder sb=new SAXBuilder();
	    Document doc=sb.build(this.getClass().getClassLoader().getResourceAsStream("beans.xml"));                                       //构造文档对象
	    Element root=doc.getRootElement(); 	//获取根元素：beans
	    List list=root.getChildren("bean");	//获取名字为：bean 的所有元素
	    for(int i=0;i<list.size();i++){	   //对元素bean进行遍历
	       Element element=(Element)list.get(i);
	       String id=element.getAttributeValue("id");
	       String clazz=element.getAttributeValue("class");
	       Object o = Class.forName(clazz).newInstance();	//反射机制、对其进行实例化
	       beans.put(id, o);				//放入Spring容器中
	       List<Element> le = element.getChildren("property");
	       for(Element propertyElement : le) {
	    	   String name = propertyElement.getAttributeValue("name");
	    	   String bean = propertyElement.getAttributeValue("bean");
	    	   Object beanObject = beans.get(bean);		    //从容其中取出对象
	    	   String methodName = "set" + name.substring(0, 1).toUpperCase() + name.substring(1);                                      //获取set方法名
	    	   Method m = o.getClass().getMethod(methodName, beanObject.getClass().getInterfaces()[0]);	
	    	   m.invoke(o, beanObject);		//执行此set方法
	       }
	    }  
	}
	
	public Object getBean(String id) {
		return beans.get(id);
	}
}

 简单Spring框架就完成了，下面就是如何使用了：

BeanFactory applicationContext = new ClassPathXmlApplicationContext();
UserService service = (UserService)applicationContext.getBean("userService");