模擬Spring控制反轉

模擬Spring控制反轉IOC

Spring中核心思想控制反轉或者稱依賴注入

/**
 * 
 * 模擬Spring控制反轉
 * @author Administrator
 *
 */
public class ClassPathXmlApplicationContext implements BeanFactory {

    private Map<String , Object> beans = new HashMap<String, Object>();


    //IOC Inverse of Control
    //DI Dependency Injection
    public ClassPathXmlApplicationContext() throws Exception {

        /**
         * 讀取所有配置，保存到list中
         */
        SAXBuilder sb=new SAXBuilder();
        Document doc=sb.build(this.getClass().getClassLoader().getResourceAsStream("beans.xml")); //構建文檔對象
        Element root=doc.getRootElement(); //獲取根元素
        List list=root.getChildren("bean");//獲取所有bean子對象

        /**
         * 遍歷bean配置，把對象保存中map中
         */
        for(int i=0;i<list.size();i++){
           Element element=(Element)list.get(i);
           String id=element.getAttributeValue("id");
           String clazz=element.getAttributeValue("class");
           Object o = Class.forName(clazz).newInstance();
           System.out.println(id);
           System.out.println(clazz);
           beans.put(id, o);

           /**
            * 當讀取到bean中存在property時，把內置對象就setter進去，由於配置關係，我們已經提前放如map中了。
            */
           for(Element propertyElement : (List<Element>)element.getChildren("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]);
               m.invoke(o, beanObject);
           }


        }  

    }



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

}

配置文件如下。

<?xml version="1.0" encoding="UTF-8"?>
<beans>
    <bean id="u" class="cn.simplemang.spring.dao.impl.UserDAOImpl" />
    <bean id="userService" class="cn.simplemang.spring.service.UserService">
        <property name="userDAO" bean="u"/>
    </bean>
</beans>