6、Spring之基於xml的自動裝配

6.1、場景模擬

6.1.1、創建UserDao介面及實現類

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、創建UserService介面及實現類

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、創建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、測試

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

6.2、兩種自動裝配方式

6.2.1、方式一：byType(常用)

6.2.1.1、配置bean

註意：
若在IOC中，沒有任何一個相容類型的bean能夠為屬性賦值，則該屬性不裝配，即值為預設值null
若在IOC中，有多個相容類型的bean能夠為屬性賦值，則拋出異常NoUniqueBeanDefinitionException

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

    <!--
        autowire屬性：指定自動裝配的策略，為bean的類類型（或介面類型）的屬性自動賦值
            byType：根據要賦值的屬性的類型，匹配ioc容器中的相容類型的bean，為屬性賦值
    -->
    <bean id="userService" class="org.rain.spring.service.impl.UserServiceImpl" autowire="byType"></bean>

    <bean id="userController" class="org.rain.spring.controller.UserController" autowire="byType"></bean>

6.2.1.2、測試

6.2.2、方式二：byName(後備)

6.2.2.1、配置bean

當在IOC中，有多個相容類型的bean能夠為屬性賦值時；可以使用byName的方式，匹配id和屬性名相同的bean為屬性賦值

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

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

    <!--
        autowire屬性：指定自動裝配的策略，為bean的類類型（或介面類型）的屬性自動賦值
            byName：根據要賦值的屬性的名稱，匹配ioc容器中的對應id的bean，為屬性賦值
    -->
    <bean id="userService" class="org.rain.spring.service.impl.UserServiceImpl" autowire="byName"></bean>