public class UserDO {
 private String name;
 private String password;
 public String getName() {
  return name;
 }
 public void setName(String name) {
  this.name = name;
 }
 public String getPassword() {
  return password;
 }
 public void setPassword(String password) {
  this.password = password;
 }
}

public class UserSelvect {
 public static void main(String[] args) {
  UserDO userDO = new UserDO();
  BeanFactory beanFactory = new ClassPathXmlApplicationContext();//创建我们的Bean工厂
  UserService userService = (UserService) beanFactory.getBean("userService");//通过类名来获得类对象
  userService.add(userDO);//完成业务逻辑
 }
}

public class UserService {
 private UserDao userDao;//实例DAO对象
 public UserDao getUserDao() {
  return userDao;
 }
 //用于Bean工厂中进行DAO动态绑定
 public void setUserDao(UserDao userDao) {
  this.userDao = userDao;
 }
 //用于Selvect对象调用，进行业务逻辑处理
 public void add(User u){
  userDao.add(u);
 }
}

/**
 * DAO类只有方法定义
 * 从而减低程序直接的耦合
 */
public interface UserDao {
 public void add(User u);
}

public class UserDaoImpl implements UserDao{
 public void add(User u){
  System.out.println("保存一个学生对象");
 }
}

<?xml version="1.0" encoding="UTF-8"?>
<beans>
 <bean id="userDao" class="com.manyiaby.daoimpl.UserDaoImpl"></bean>
 <bean id="userService" class="com.manyiaby.service.UserService">
  <property name="userDao" bean="userDao"></property>
 </bean>
</beans>

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

public class ClassPathXmlApplicationContext implements BeanFactory{
 private Map<String, Object> beanMap = new HashMap<String, Object>();//用来存配置文件中的类对象
 public ClassPathXmlApplicationContext(){
  try {
   SAXBuilder saxBulder = new SAXBuilder();
   Document doc = saxBulder.build(ClassPathXmlApplicationContext.class
     .getClassLoader().getResourceAsStream("spring.xml"));
   Element root = doc.getRootElement();//获取根元素
   List<Element> list = root.getChildren("bean");
   for (Element element : list) {
    String id = element.getAttributeValue("id");//得到beanId
    String className = element.getAttributeValue("class");//得到Bean的类名地址
    System.out.println(className);
    Object object = Class.forName(className).newInstance();
    beanMap.put(id, object);
    if (null != element.getChild("property")) {
     Element property = element.getChild("property");
     String name = property.getAttributeValue("name");
     String beanId = property.getAttributeValue("bean");
     Object beanObject = beanMap.get(beanId);//UserDaoImpl
     String methodName = "set" + name.substring(0, 1).toUpperCase() + name.substring(1);//setUserDao
     System.out.println(methodName);
     Method m = object.getClass().getMethod(methodName, beanObject.getClass().getInterfaces()[0]);//UserService的SetUserDao()方法，接收的参数为UserDao接口类
     m.invoke(object, beanObject);//调用UserService的SetUserDao()方法，传入UserDaoImpl
    }
   }
  } catch (Exception e) {
   System.out.println("" + e);
  }
 }
 //用于类调用
 @Override
 public Object getBean(String className) {
  return beanMap.get(className);
 }
}

public class UserSelvect {
 public void main() {
  UserDO userDO = new UserDO();
  BeanFactory beanFactory = new ClassPathXmlApplicationContext("spring.xml");
  UserService userService = (UserService) beanFactory.getBean("userService");
  //ApplicationContext context = new ClassPathXmlApplicationContext("spring.xml");
  //UserService userService = (UserService) context.getBean("userService");
  userService.add(userDO);
 }
}