spring bean

模拟Spring的读取xml文件及注入（转）

（转）

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);
    }
}