01spring spring的简单模拟

spring的设计是面向接口(抽象)的
好处：灵活，可以更换不同的实现

模拟spring读取xml配置文件

beans.xml//可以看成是一个大的容器
<beans>
	<bean id="u" class="com.dao.impl.UserDAOImpl"/>
	<bean id="userService" class="com.service.UserService">
		<property name="userDAO" bean="u"/>
		//把userDAO装配(注入)到userService中
	</bean>
</beans>

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

public class ClassPathXmlApplicationContext implements BeanFactory
{
	private Map<String,Object> beans = new HashMap<String,Object>();
	
	public ClassPathXmlApplicationContext() throws Exception{
		SAXBuilder builder = new SAXBuilder();
		Document doc = 
		builder.build(Sample.class.getClassLoader().getResourceAsStream("beans.xml"));
		//构造文档对象
		Element root = doc.getRootElement();//获取根元素
		List list = root.getChildren("bean");//取名字为bean的所有元素
		for(int i=0;i<list.size();i++){
			Element element = (Element)list.get(i);
			String id = element.getAttributeValue("id");
			String clazz = element.getChildText("class");
			System.out.println(id+":"+clazz);
			Object o = Class.forName(clazz).newInstance();
			beans.put(id,o);

			for(Element propertyElement:(List<Element>)element.getChild("property")){
				String name = propertyElement.getAttributeValue("name");//userDAO
				String bean = propertyElement.getAttributeValue("bean");//u
				Object beanObject = beans.get(bean);//UserDAOImpl instance

				String methodName = "set"+name.substring(0,1).toUpperCase()+name.substring(1);
				System.out.println("method name = "+methodName);

				Method m = o.getClass().getMethod(methodName,beanObject.getClass().getInterfaces()[0]);
				//根据方法名和参数获取方法(因为可能存在重载)
				//参数是userDAOImpl实现的接口中的一个
				m.invoke(o,beanObject);
				//调用o对象的m方法，传入参数beanObject
			}
		}
	}

	public Object getBean(String name)
	{
		return beans.get(name);
	}
}

public class UserServiceTest
{
	@Test
	public void testAdd() throws Exception
	{
		BeanFactory factory = new ClassPathXmlApplicationContext();
		UserService service = new UserService();
		//UserDAO userDAO = (UserDAO)factory.getBean("u");
		//service.setUserDAO(userDAO);
		User u = new User();
		service.add(u);
	}
}