模拟Spring实现

我们知道Spring最主要的就是帮我们管理Service，Dao，还有Action。

今天我们就来模拟一下Spring实现的原理，其实就是解析xml和反射机制。

以用户添加为例，直接上代码：

1.User.java

public class User {
	
	private String username;
	private String password;
	
	public String getUsername() {
		return username;
	}
	public void setUsername(String username) {
		this.username = username;
	}
	public String getPassword() {
		return password;
	}
	public void setPassword(String password) {
		this.password = password;
	}
	
}

2.UserDAO.java

import com.yuwl.model.User;

public interface UserDAO {
	public void save(User user);
}

3.UserDAOImpl.java

import com.yuwl.dao.UserDAO;
import com.yuwl.model.User;

public class UserDAOImpl implements UserDAO {

	public void save(User user) {
		//Hibernate or Jdbc add
		System.out.println("user saved!");
	}

}

package com.yuwl.service;

import com.yuwl.dao.UserDAO;
import com.yuwl.model.User;

public class UserService {
	
	private UserDAO userDAO;  
	
	public void add(User user) {
		userDAO.save(user);
	}
	public UserDAO getUserDAO() {
		return userDAO;
	}
	public void setUserDAO(UserDAO userDAO) {
		this.userDAO = userDAO;
	}
}

5.仿Spring配置文件beans.xml

<beans>

	<bean id="u" class="com.yuwl.dao.impl.UserDAOImpl" />
	
	<bean id="userService" class="com.yuwl.service.UserService" >
		<property name="userDAO" bean="u"/>
	</bean>
	
</beans>

6.仿Spring的BeanFactory.java

package com.yuwl.spring;

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

7.仿Spring的ClassPathXmlApplicationContext.java

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>();
	
	public ClassPathXmlApplicationContext() throws Exception {
	    //jdom解析xml
            SAXBuilder sb=new SAXBuilder();
	    Document doc=sb.build(this.getClass().getClassLoader().getResourceAsStream("beans.xml")); 
	    Element root=doc.getRootElement(); 
	    List list=root.getChildren("bean");
	    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();
	       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);
	    	   //反射
	    	   Method m = o.getClass().getMethod(methodName, beanObject.getClass().getInterfaces()[0]);
	    	   m.invoke(o, beanObject);
	       }
	       
	    }  
	  
	}

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

}

8.测试

import org.junit.Test;
import com.yuwl.model.User;
import com.yuwl.spring.BeanFactory;
import com.yuwl.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("yuwl");
		u.setPassword("123456");
		service.add(u);
	}

}

执行成功：

user saved!

接下来，将深入Spring的IOC学习。

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