6.1、场景模拟

6.1.1、创建UserDao接口及实现类

package org.rain.spring.dao;

/**
 * @author liaojy
 * @date 2023/8/5 - 11:05
 */
public interface UserDao {

    void saveUser();

}

package org.rain.spring.dao.impl;

import org.rain.spring.dao.UserDao;

/**
 * @author liaojy
 * @date 2023/8/5 - 11:08
 */
public class UserDaoImpl implements UserDao {

    public void saveUser() {
        System.out.println("保存成功");
    }

}

6.1.2、创建UserService接口及实现类

package org.rain.spring.service;

/**
 * @author liaojy
 * @date 2023/8/5 - 11:10
 */
public interface UserService {

    void saveUser();

}

package org.rain.spring.service.impl;

import org.rain.spring.dao.UserDao;
import org.rain.spring.service.UserService;

/**
 * @author liaojy
 * @date 2023/8/5 - 11:23
 */
public class UserServiceImpl implements UserService {

    private UserDao userDao;

    public UserDao getUserDao() {
        return userDao;
    }

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

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

6.1.3、创建UserController

package org.rain.spring.controller;

import org.rain.spring.service.UserService;

/**
 * @author liaojy
 * @date 2023/8/5 - 11:32
 */
public class UserController {

    private UserService userService;

    public UserService getUserService() {
        return userService;
    }

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

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

6.1.4、配置bean

<?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="org.rain.spring.dao.impl.UserDaoImpl"></bean>

    <bean id="userService" class="org.rain.spring.service.impl.UserServiceImpl">
        <property name="userDao" ref="userDao"></property>
    </bean>

    <bean id="userController" class="org.rain.spring.controller.UserController">
        <property name="userService" ref="userService"></property>
    </bean>

</beans>

6.1.5、测试

    @Test
    public void testAutoWireByXML(){
        ApplicationContext ioc = new ClassPathXmlApplicationContext("spring-autowire.xml");
        UserController userController = ioc.getBean(UserController.class);
        userController.saveUser();
    }

6.2、两种自动装配方式

6.2.1、方式一：byType(常用)

6.2.1.1、配置bean

注意：
若在IOC中，没有任何一个兼容类型的bean能够为属性赋值，则该属性不装配，即值为默认值null
若在IOC中，有多个兼容类型的bean能够为属性赋值，则抛出异常NoUniqueBeanDefinitionException

    <bean id="userDao" class="org.rain.spring.dao.impl.UserDaoImpl"></bean>

    <!--
        autowire属性：指定自动装配的策略，为bean的类类型（或接口类型）的属性自动赋值
            byType：根据要赋值的属性的类型，匹配ioc容器中的兼容类型的bean，为属性赋值
    -->
    <bean id="userService" class="org.rain.spring.service.impl.UserServiceImpl" autowire="byType"></bean>

    <bean id="userController" class="org.rain.sprin