public class ClassPathXmlApplicationContext implements BeanFactory {
 
 private Map<String , Object> beans = new HashMap<String, Object>();
 
 //IOC Inverse of Control DI Dependency Injection
 public ClassPathXmlApplicationContext() throws Exception {
  SAXBuilder sb=new SAXBuilder();
  //解析xml配置文件
  Document doc=sb.build(this.getClass().getClassLoader().getResourceAsStream("beans.xml"));
  Element root=doc.getRootElement(); //獲取根元素
  List list=root.getChildren("bean");//根元素下的子元素
  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(); //反射獲得實例
   System.out.println(id);
   System.out.println(clazz);
   beans.put(id, o);
   //注入bean屬性
   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);
 }
}

//xml文件
<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>

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("zhangsan");
  u.setPassword("zhangsan");
  service.add(u);
 }
 
 @Test
 public void testProxy() {
  UserDAO userDAO = new UserDAOImpl();
  LogInterceptor li = new LogInterceptor();
  li.setTarget(userDAO);
  UserDAO userDAOProxy = (UserDAO)Proxy.newProxyInstance(userDAO.getClass().getClassLoader(), userDAO.getClass().getInterfaces(), li);
  
  userDAOProxy.delete();
  userDAOProxy.save(new User());
 }

public class LogInterceptor implements InvocationHandler {
 private Object target;
 public Object getTarget() {
  return target;
 }
 public void setTarget(Object target) {
  this.target = target;
 }

 public void beforeMethod(Method m) {
  System.out.println(m.getName() + " start");
 }

 @Override
 public Object invoke(Object proxy, Method m, Object[] args)
   throws Throwable {
  beforeMethod(m);
  m.invoke(target, args);
  return null;
 }
}