Spring IOC(DI)模拟

Spring DI Simulation

解释：IOC Inverse Of Control（控制反转） 或者 DI Dependency Injection（依赖注入）
观察以下代码，发现UserService类并没有对自己的属性UserDAO进行初始化，但是UserDAO仍然不为null，因为ClassPathXmlApplicationContext类初始化的时候，通过读取配置文件bean.xml将UserDAO对象注入到UserService对象里面。所以明面上没有对其进行初始化，使用配置文件初始化类对象，易于控制，不必修改类代码，可扩展性强。
User类

package com.edu.hpu.model;

public class User {

	private String name;

	public String getName() {
		return name;
	}

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

UserDAO接口

package com.edu.hpu.dao;

import com.edu.hpu.model.User;

public interface UserDAO {

	public void save(User user);
	
}
UserDAOImpl类Implements UserDAO
package com.edu.hpu.impl;

import com.edu.hpu.dao.UserDAO;
import com.edu.hpu.model.User;

public class UserDAOImpl implements UserDAO {

	public void save(User user) {
		System.out.println("user saved!");
	}
	
}

4、UserService类

package com.edu.hpu.service;

import com.edu.hpu.dao.UserDAO;
import com.edu.hpu.model.User;

public class UserService {

	private UserDAO userDAO;
	
	public void save(User user) {
		userDAO.save(user);
	}

	public UserDAO getUserDAO() {
		return userDAO;
	}

	public void setUserDAO(UserDAO userDAO) {
		this.userDAO = userDAO;
	}
}

BeanFactory接口

package com.hpu.spring;

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

ClassPathXmlApplicationContext类 Implements BeanFactory（重点）

package com.hpu.spring;

import java.io.IOException;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import org.jdom2.Document;
import org.jdom2.Element;
import org.jdom2.JDOMException;
import org.jdom2.input.SAXBuilder;

import com.edu.hpu.dao.UserDAO;

public class ClassPathXmlApplicationContext implements BeanFactory {

	Map<String , Object> beans = new HashMap<String , Object>();
	
	public ClassPathXmlApplicationContext() {
		SAXBuilder sax = new SAXBuilder();
		try {
			Document doc = sax.build("beans.xml");
			Element root = doc.getRootElement();
			
			List<Element> children = root.getChildren();
			for(int i = 0; i < children.size(); i++) {
				Element child = children.get(i);
				
				String key = child.getAttributeValue("id");
				String className = child.getAttributeValue("class");
				//System.out.println(key + "   " + className);
				Object value = Class.forName(className).newInstance();
				//System.out.println(value);
				beans.put(key, value);
				
				for(Element pro : child.getChildren("property")) {
					if(pro != null) {
						String name = pro.getAttributeValue("name");
						String beanName = pro.getAttributeValue("bean");
						char c = name.charAt(0);
						c = Character.toUpperCase(c);
						name = "set" + c + name.substring(1);
						Object bean = beans.get(beanName);
						Method methodName = value.getClass().getMethod(name, bean.getClass().getInterfaces()[0]);
						methodName.invoke(value, bean);
						System.out.println(name);
						System.out.println(bean);
					}
				}
			}
		} catch (JDOMException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		} catch(ClassNotFoundException e) {
			e.printStackTrace();
		} catch (InstantiationException e) {
			e.printStackTrace();
		} catch (IllegalAccessException e) {
			e.printStackTrace();
		} catch (SecurityException e) {
			e.printStackTrace();
		} catch (IllegalArgumentException e) {
			e.printStackTrace();
		} catch (NoSuchMethodException e) {
			e.printStackTrace();
		} catch (InvocationTargetException e) {
			e.printStackTrace();
		}
	}
	
	@Override
	public Object getBean(String name) {
		return beans.get(name);
	}
}

bean.xml配置文件

<?xml version="1.0" encoding="UTF-8"?>
<beans>
	<bean id="u" class="com.edu.hpu.impl.UserDAOImpl"></bean>
	
	<bean id="userService" class="com.edu.hpu.service.UserService">
		<property name="userDAO" bean="u"/>
	</bean>
</beans>

测试类

package com.edu.hpu.sevice;

import org.junit.Test;

import com.edu.hpu.model.User;
import com.edu.hpu.service.UserService;
import com.hpu.spring.BeanFactory;
import com.hpu.spring.ClassPathXmlApplicationContext;

public class TestUser {

	@Test
	public void testSave() {
		BeanFactory bf = new ClassPathXmlApplicationContext();
		
		UserService service = (UserService)bf.getBean("userService");
		User u = new User();
		service.save(u);
	}
	
}