Spring的IOC实现（Java反射机制）

ClassPathXmlApplicationContext：

View Code

package com.bjsxt.spring;



import java.lang.reflect.Method;

import java.util.HashMap;

import java.util.List;

import java.util.Map;

import org.jdom.Document;

import org.jdom.Element;

import org.jdom.input.SAXBuilder;



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 {

        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HD

        List list=root.getChildren("bean");//取名字为disk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.getAttributeValue("class");

           Object o = Class.forName(clazz).newInstance();

           System.out.println(id);

           System.out.println(clazz);

           beans.put(id, o);

           

           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);

    }



}

beans.xml:

View Code

<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>

测试：

View Code

package com.bjsxt.service;

import org.junit.Test;



import com.bjsxt.dao.UserDAO;

import com.bjsxt.model.User;

import com.bjsxt.spring.BeanFactory;

import com.bjsxt.spring.ClassPathXmlApplicationContext;

public class UserServiceTest {



    @Test

    public void testAdd() throws Exception {

        BeanFactory applicationContext = new ClassPathXmlApplicationContext();

        UserService service = (UserService)applicationContext.getBean("userService");

        User u = new User();

        u.setUsername("zhangsan");

        u.setPassword("zhangsan");

        service.add(u);

    }



}

通过ClassPathXmlApplicationContext读取beans.xml配置文件中的依赖关系完成将实现代码：

View Code

package com.bjsxt.dao.impl;



import com.bjsxt.dao.UserDAO;

import com.bjsxt.model.User;





public class UserDAOImpl implements UserDAO {



    public void save(User user) {

        //Hibernate

        //JDBC

        //XML

        //NetWork

        System.out.println("user saved!");

    }



}

注入：

View Code

package com.bjsxt.dao;

import com.bjsxt.model.User;





public interface UserDAO {

    public void save(User user);

}