8.1、场景模拟

8.1.1、UserDao接口及实现类

package org.rain.spring.dao;

/**
 * @author liaojy
 * @date 2023/8/5 - 18:32
 */
public interface UserDao {

    void saveUser();

}

package org.rain.spring.dao.impl;

import org.rain.spring.dao.UserDao;
import org.springframework.stereotype.Repository;

/**
 * @author liaojy
 * @date 2023/8/5 - 18:33
 */
@Repository
public class UserDaoImpl implements UserDao {
    public void saveUser() {
        System.out.println("保存成功");
    }
}

8.1.2、UserService接口及实现类

package org.rain.spring.service;

/**
 * @author liaojy
 * @date 2023/8/5 - 18:35
 */
public interface UserService {

    void saveUser();

}

package org.rain.spring.service.impl;

import org.rain.spring.dao.UserDao;
import org.rain.spring.service.UserService;
import org.springframework.stereotype.Service;

/**
 * @author liaojy
 * @date 2023/8/5 - 18:36
 */
@Service
public class UserServiceImpl implements UserService {

    private UserDao userDao;

    public void saveUser() {
        userDao.saveUser();
    }

}

8.1.3、UserController

package org.rain.spring.controller;

import org.rain.spring.service.UserService;
import org.springframework.stereotype.Controller;

/**
 * @author liaojy
 * @date 2023/8/5 - 18:38
 */
@Controller("myUserController")
public class UserController {

    private UserService userService;

    public void saveUser(){
        userService.saveUser();
    }

}

8.1.4、bean配置

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

    <!--
        对指定的package进行扫描，将使用组件注解的类的对象，交给spring的ioc容器来管理
    -->
    <context:component-scan base-package="org.rain.spring"></context:component-scan>

</beans>

8.1.5、测试

由控制台日志可知，组件注解+组件扫描，存在尚未实现依赖注入的问题

    @Test
    public void testAutowireByAnnotation(){

        ApplicationContext ioc = new ClassPathXmlApplicationContext("spring-ioc-annotation.xml");
        UserController userController = ioc.getBean(UserController.class);
        userController.saveUser();

    }

8.2、@Autowired注解

@Autowired：实现自动装配功能的注解，其能够标识的位置有三处

8.2.1、方式一：标识在成员变量上(常用)

    @Autowired
    private UserDao userDao;

    @Autowired
    private UserService userService;

8.2.2、方式二：标识在setter方法上

    private UserDao userDao;

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

    private UserService userService;

    @Autowired
    public void setUserService(UserService userService) {
        this.userService = userService;
    }

8.2.3、方式三：标识在有参构造方法上

    private UserDao userDao;

    @Autowired
    public UserServiceImpl(UserDao userDao) {
        this.userDao = userDao;
    }

    private UserService userService;

    @Autowired
    public UserController(UserService userService) {
        this.userService = userService;
    }

8.3、@Autowired的工作流程

• 默认通过byType的方式，在IOC容器中匹配类型相同的bean，为属性赋值

• 如果有多个类型匹配的bean，则自动转换为通过b