Spring 架构的简单模拟实现

  Spring 架构主要有两大特点: 

    IOC /DI: 控制反转/依赖注入 

   AOP  切面编程 .

  

    今天主要是实现IOC这一特点.

    主要的逻辑如下:

    User 用户类.

    UserDAO  User类的访问接口. 

    UserDAOImpl  实现UserDAO 接口以实现拓展. 

    UserService  包含一系列的用户功能 ,如addUser

   关于以上类的代码:

   

package com.bjsxt.model;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;}}

 

package com.bjsxt.dao;import com.bjsxt.model.User;public interface UserDAO {public void save(User user);}

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//NetWorkSystem.out.println("user saved!");}}

package com.bjsxt.service;import com.bjsxt.dao.UserDAO;import com.bjsxt.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;}}

然后运行test代码

import com.bjsxt.dao.UserDAO;import com.bjsxt.dao.impl.UserDAOImpl;import com.bjsxt.model.User;import com.bjsxt.service.UserService;import com.bjsxt.spring.BeanFactory;import com.bjsxt.spring.ClassPathXmlApplicationContext;public class Test {public static void main(String[] args)throws Exception{UserService service =new UserService();UserDAO userdao =new UserDAOImpl();service.setUserDAO(userdao);User u =new User();service.add(u);}}

注意这里直接用UserDAOImpl() 来代替UserDAO , 也是体现面向对象的灵活性.  比如可以针对不同的数据库设计不同的UserDAOImpl(). 

为了实现IOC 的装配功能, 比如说我不想在 代码中体现new 的是哪种UserDAO的实现, 而是直接在配置文件中进行设置.

配置文件beans.xml如下:

  <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>

这里可以根据bean 的id  userService  找到 所属的UserService类, 在属性userDAO中  ,设置其为id 为 "u"的bean . 而上述文件中的 id 为"u"的bean , 就是UserDAOImp .

当然, 需要借助Factory 接口 和该接口的实现类 ClassPathXmlApplicationContext .

package com.bjsxt.spring;public interface BeanFactory {public Object getBean(String id);}

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 Injectionpublic 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bean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);}}

ClassPathXmlApplicationContext 利用反射机制, 在构造函数中根据xml文件内容实现装配功能.

新的test函数:

import com.bjsxt.dao.UserDAO;import com.bjsxt.dao.impl.UserDAOImpl;import com.bjsxt.model.User;import com.bjsxt.service.UserService;import com.bjsxt.spring.BeanFactory;import com.bjsxt.spring.ClassPathXmlApplicationContext;public class Test {public static void main(String[] args)throws Exception{BeanFactory factory =new ClassPathXmlApplicationContext();UserService service =(UserService)factory.getBean("userService");//UserDAO userdao =new UserDAOImpl();//service.setUserDAO(userdao);User u =new User();service.add(u);}}