Java 自定义Spring框架以及Spring框架的基本使用

<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-context</artifactId>
    <version>5.3.9</version>
</dependency>

package com.meimeixia.dao;

/**
 * 数据访问层接口
 * @author liayun
 * @create 2021-09-19 18:17
 */
public interface UserDao {

    public void add();

}

package com.meimeixia.dao.impl;

import com.meimeixia.dao.UserDao;

/**
 * 数据访问层实现类
 * @author liayun
 * @create 2021-09-19 18:29
 */
public class UserDaoImpl implements UserDao {

    @Override
    public void add() {
        System.out.println("UserDao...");
    }

}

package com.meimeixia.service;

/**
 * 业务逻辑层接口
 * @author liayun
 * @create 2021-09-19 18:31
 */
public interface UserService {

    public void add();

}

package com.meimeixia.service.impl;

import com.meimeixia.dao.UserDao;
import com.meimeixia.service.UserService;

/**
 * 业务逻辑层实现类
 * @author liayun
 * @create 2021-09-19 18:37
 */
public class UserServiceImpl implements UserService {

    // 因为业务逻辑层是要调用数据访问层中的功能的，所以在这儿我们得声明一个UserDao类型的变量
    private UserDao userDao; // 注意了，这儿我们并没有为该变量进行赋值，赋值的操作得交给Spring去做，只是这样做的前提是我们得为该变量提供一个setter方法

    public void setUserDao(UserDao userDao) {
        this.userDao = userDao;
    }

    @Override
    public void add() {
        System.out.println("UserService...");
        userDao.add();
    }

}

<?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 id="userDao" class="com.meimeixia.dao.impl.UserDaoImpl"></bean>

    <bean id="userService" class="com.meimeixia.service.impl.UserServiceImpl">
        <property name="userDao" ref="userDao"></property>
    </bean>

</beans>

package com.meimeixia.controller;

import com.meimeixia.service.UserService;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

/**
 * @author liayun
 * @create 2021-09-19 18:41
 */
public class UserController {
    public static void main(String[] args) throws Exception {
        // 1. 创建Spring的容器对象
        ApplicationContext applicationContext = new ClassPathXmlApplicationContext("applicationContext.xml");
        // 2. 从容器对象中获取UserService对象
        UserService userService = applicationContext.getBean("userService", UserService.class);
        // 3. 调用UserService对象的方法进行业务逻辑处理
        userService.add();
    }
}