BeanFactory bf = new ClassPathXmlApplicationContext("spring.xml");
User userBean = (User) bf.getBean("userBean");

BeanFactory bf = new ClassPathXmlApplicationContext("user.xml");
User userBean = (User) bf.getBean("userFactoryBean");

public class DefaultSingletonBeanRegistry {
    
    // 使用 ConcurrentHashMap 保存各種單實(shí)例對(duì)象
    private final Map<String, Object> singletonObjects = new ConcurrentHashMap<String, Object>;

    protected Object getSingleton(String beanName) {
    // 先到 Map 中拿Object
    Object singletonObject = singletonObjects.get(beanName);
    
    // 若沒拿到通過反射創(chuàng)建一個(gè)對(duì)象實(shí)例，并添加到HashMap中
    if (singletonObject == null) {
      singletonObjects.put(beanName,
                           Class.forName(beanName).newInstance());
   }
   
   // 返回對(duì)象實(shí)例
   return singletonObjects.get(beanName);
  }
}

// 抽象接口
public interface IStudentDao {
    void save();
}

// 目標(biāo)對(duì)象
public class StudentDao implements IStudentDao {
    public void save() {
        System.out.println("保存成功");
    }
}

// 代理對(duì)象
public class StudentDaoProxy implements IStudentDao{
    //持有目標(biāo)對(duì)象的引用
    private IStudentDao target;
    public StudentDaoProxy(IStudentDao target){
        this.target = target;
    }

    //在目標(biāo)功能對(duì)象方法的前后加入事務(wù)控制
    public void save() {
        System.out.println("開始事務(wù)");
        target.save();//執(zhí)行目標(biāo)對(duì)象的方法
        System.out.println("提交事務(wù)");
    }
}

public static void main(String[] args) {
    //創(chuàng)建目標(biāo)對(duì)象
    StudentDao target = new StudentDao();

    //創(chuàng)建代理對(duì)象,把目標(biāo)對(duì)象傳給代理對(duì)象,建立代理關(guān)系
    StudentDaoProxy proxy = new StudentDaoProxy(target);
   
    //執(zhí)行的是代理的方法
    proxy.save();
}

public class MyInvocationHandler implements InvocationHandler {

    private Object obj;

    public MyInvocationHandler(Object obj){
        this.obj=obj;
    }

    @Override
    public Object invoke(Object proxy, Method method, Object[] args)
            throws Throwable {

        System.out.println("開始事務(wù)");
        Object result = method.invoke(obj, args);
        System.out.println("開始事務(wù)");
        
        return result;
    }
}

public static void main(String[] args) {
  //創(chuàng)建目標(biāo)對(duì)象StudentDao
  IStudentDao stuDAO = new StudentDao();
  
  //創(chuàng)建MyInvocationHandler對(duì)象
  InvocationHandler handler = new MyInvocationHandler(stuDAO);
  
  //使用Proxy.newProxyInstance動(dòng)態(tài)的創(chuàng)建代理對(duì)象stuProxy
  IStudentDao stuProxy = (IStudentDao) 
 Proxy.newProxyInstance(stuDAO.getClass().getClassLoader(), stuDAO.getClass().getInterfaces(), handler);
  
  //動(dòng)用代理對(duì)象的方法
  stuProxy.save();
}