Spring

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">

<!-- bean definitions here -->

    <bean id="userServiceId" class="com.guigu.bean.UserServiceImpl">
        <!-- DI依赖注入 -->
        <property name="ud" ref="userDaoId"></property>
    </bean>
    <!-- userDao配置 -->
    <bean id="userDaoId" class="com.guigu.bean.UserDaolmpl"></bean>

</beans>

public interface UserDao {
    public void add();
    public void update();
    public void delete();

}

public class UserDaolmpl implements UserDao{

    public void add() {
        // TODO Auto-generated method stub
        System.out.println("这是dao层的add方法");
    }

    public void update() {
        // TODO Auto-generated method stub
        System.out.println("这是dao层的update方法");
    }

    public void delete() {
        // TODO Auto-generated method stub
        System.out.println("这是dao层的delete方法");
    }

}

public interface UserService {
    //面向接口编程  灵活  解耦
    public void add();
    public void update();
    public void delete();

}

public class UserServiceImpl implements UserService{

    //DI依赖注入
    private UserDao ud;
    
    public UserDao getUd() {
        return ud;
    }

    public void setUd(UserDao ud) {
        this.ud = ud;
    }

    public void add() {
        // TODO Auto-generated method stub
        System.out.println("这是service的add方法");
        //普通的方式
        //UserDao ud=new UserDaolmpl();
        //ud.add();
        ud.add();
    }

    public void update() {
        // TODO Auto-generated method stub
        System.out.println("这是servicce的update方法");
    }

    public void delete() {
        // TODO Auto-generated method stub
        System.out.println("这是servicce的delete方法");
    }

}