模拟Spring的读取xml文件及注入

简单的xml配置文件

<?xml version="1.0" encoding="UTF-8"?>
<beans>
	<bean id="userDAO" class="com.king.dao.impl.UserDAOImpl"></bean>
	
	<bean id="userService" class="com.king.service.impl.UserServiceImpl">
		<property name="userDAO" ref="userDAO"></property>
	</bean>
</beans>

BeanFactory接口

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

实现BeanFactory的接口

public class ClassPathXmlApplicationContext implements BeanFactory{
	private Map<String,Object> beans = new HashMap<String,Object>(); // map for store beans
	
         /***constructor****/
	public ClassPathXmlApplicationContext() 
	{
		SAXBuilder sb = new SAXBuider();
		Document doc = sb.builder(this.getClass().getClassLoader().getResourceAsStream("beans.xml"));//read the xml file in classpath
		Element root = doc.getRootElement(); // beans
		List list = root.getChildren("bean"); // all beans in that list
		
		int size = list.size();
		
		for(int i = 0; i< size; i++)
		{
			Element element = list.get(i);
			
			String id = element.getAttributeValue("id"); // get id
			String clazz = element.getAttributeValue("class"); // get class
			
			Object o = Class.forName(clazz).newInstance(); // reflect 
			beans.put(id,o); // put into the map
			
			List<Element> properties = (List<Element>) element.getChildren("property"); // get property config,for DI
			
			for(Element property : properties)
			{
				String name = property.getAttributeValue("name"); // get name
				String ref = property.getAttributeValue("ref"); // get reference bean name
				
				Object refBean = beans.get(ref); // get reference bean form map
				
				String methodName = "set" + name.subString(0,1).toUpperCase() + name.subString(1); // setter method name
				System.out.println(methodName);
				
				Method m = o.getClass().getMethod(methodName,refBean.getClass.getInterfaces()[0]); // get method parameters 
				m.invoke(o,refBean); // execute to inject reference bean 
			}
		}
	}
	
	public Object getBean(String name)
	{
		return beans.get(name);
	}

调用测试：

public SpringTest{
  
    @Test
    public void testAdd()
    {
        BeanFactory factory = new ClassPathXmlApplicationContext();
        UserService service = (UserService) factory.getBean("userService");

        User u = new User();
        service.add(u);
    }
}