模拟spring

  利用dom4j简单模拟了一下spring是如何注入的，并用junit简单进行了一下测试。

  定义一个BeanFactory接口，包含一个得到bean的方法

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

 定义一个ClassPathXmlApplicationContext类，利用dom4j解析bean.xml文件，用反射生成所需要的实例对象放入到beans容器中

package com.test.myspring;

import java.io.FileInputStream;
import java.lang.reflect.Method;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;

import org.dom4j.Document;
import org.dom4j.Element;
import org.dom4j.io.SAXReader;

public class ClassPathXmlApplicationContext implements BeanFactory{
	
	private Map<String,Object> beans = new HashMap<String,Object>();
	
	@SuppressWarnings("rawtypes")
	public ClassPathXmlApplicationContext(){
		SAXReader reader = new SAXReader(); 
        Document document;
		try {
			document = reader.read(new FileInputStream("bean.xml")); //得到xml文档，xml文件置于工程根目录下
	        Element root = document.getRootElement();			     //得到根元素
	        for(Iterator i = root.elementIterator();i.hasNext();){
	        	Element element = (Element)i.next();
	        	String id = element.attributeValue("id");         //userDao
	        	String clazz = element.attributeValue("class");   //com.test.myspring.UserDAOImpl
	        	Object o = Class.forName(clazz).newInstance();    //生成UserDAOImpl的一个实例
	        	beans.put(id, o);
	        	
	        	for(Iterator ei = element.elementIterator();ei.hasNext();){ //遍历子元素
	        		Element childe = (Element)ei.next();
	        		String name = childe.attributeValue("name");   //本例中是得到userDao
	        		String bean = childe.attributeValue("bean");   
	        		Object objectBean = beans.get(bean);           //从beans容器中得到UserDAOImpl的实例
	        		
	        		String methodName = "set"+name.substring(0, 1).toUpperCase()
	        								 +name.substring(1);       //得到setUserDao方法名
	        		Method method = o.getClass().getMethod(methodName, 
	        				objectBean.getClass().getInterfaces()[0]); //通过反射得到该方法
	        		
	        		method.invoke(o, objectBean);   
	        	}
	        }	
		} catch (Exception e) {
			e.printStackTrace();
		} 
	}

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

}

 

bean.xml文件

<?xml version="1.0" encoding="UTF-8"?>
<beans>
	<bean id="userDao" class="com.test.myspring.UserDAOImpl"/>
	<bean id="userService" class="com.test.myspring.UserService">
		<property name="userDao" bean="userDao"/>
	</bean>
</beans>

 另外有User、UserDAO、UserDAOImpl、UserService

public class User {
	private String name;

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}
	
}


public interface UserDAO {
	void add(User u);
}


public class UserDAOImpl implements UserDAO {

	@Override
	public void add(User u) {
		System.out.println("A user has saved!");
	}

}

public class UserService {
	private UserDAO userDao;

	public UserDAO getUserDao() {
		return userDao;
	}

	public void setUserDao(UserDAO userDao) {
		this.userDao = userDao;
	}
	
	public void add(User u){
		this.userDao.add(u);
	}
}

 

写一个简单的类UserServiceTest测试下

import org.junit.Test;

public class UserServiceTest {
	@Test
	public void testAdd(){
		BeanFactory factory = new ClassPathXmlApplicationContext(); 
		//首先直接得到了UserService的一个实例us
		//然后通过ClassPathXmlApplicationContext中的第二个for循环自动装配了userDao
		UserService us = (UserService)factory.getBean("userService");
		User u = new User();
		us.add(u);
	}
}

 

 

运行输出A user has saved! 这里并没有真正去连接数据库。