Spring核心概念、IoC和DI的认识、Spring中bean的配置及实例化、bean的生命周期

一、Spring核心概念

1.1IoC(Inversion of Contral)：控制反转

• 代码书写现状
• • 耦合度偏高
• 解决方案
• • 使用对象时，在程序中不要主动使用new产生对象，转换为由外部提供对象

---

• IoC(Inversion of Contral)：控制反转
• • 对象的创建控制权由程序转移到外部，这种思想称为控制反转
• Spring技术对IoC思想进行了实现
• • Spring提供了一个容器，称为IoC容器，用来充当IoC思想中的“外部”
• • IoC容器负责对象的创建、初始化等一系列工作，被创建或被管理的对象在IoC容器中统称为Bean
• DI(Dependency Injection)依赖注入
• • 在容器中建立bean与bean之间的依赖关系的整个过程，称为依赖注入

1.2IoC代码实现

• 1.导入Spring坐标

<dependency><groupId>org.springframework</groupId><artifactId>spring-context</artifactId><version>5.2.21.RELEASE</version>
</dependency>

• 2.定义Spring管理类

package com.practice.dao;/*** @Author YJ* @Date 2023/7/25 11:26* Description:*/
public interface BookDao {void save();
}

package com.practice.service;/*** @Author YJ* @Date 2023/7/25 11:28* Description:*/
public interface BookService {void save();
}

package com.practice.service.impl;import com.practice.dao.BookDao;
import com.practice.dao.impl.BookDaoImpl;
import com.practice.service.BookService;/*** @Author YJ* @Date 2023/7/25 11:28* Description:*/
public class BookServiceImpl implements BookService {private BookDao bookDao = new BookDaoImpl();public void save() {bookDao.save();}
}

• 3.创建Spring配置文件applicationContext.xml，配置对应类作为Spring管理的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"><!--1.导入spring的坐标spring-context，对应的版本号是5.2.21.RELEASE--><!--2.配置bean--><bean id="bookDao" class="com.practice.dao.impl.BookDaoImpl"/><bean id="bookService" class="com.practice.service.impl.BookServiceImpl"/>
</beans>

• 4.初始化IoC容器（Spring核心容器/Spring容器），通过容器获取bean

public class App {public static void main(String[] args) {//获取IoC容器ApplicationContext act = new ClassPathXmlApplicationContext("applicationContext.xml");//获取bean/*BookDao bookDao = (BookDao) act.getBean("bookDao");bookDao.save();*/BookService bookService = (BookService) act.getBean("bookService");bookService.save();}
}

1.2DI代码实现

• 1.删除业务层中使用new的方式创建的dao对象
• 2.提供对应的setter方法
• 3.配置service与dao的关系
• • property标签表示配置当前bean的属性
• • name属性表示配置哪一个具体的属性
• • ref属性表示参照哪一个bean

package com.practice.service.impl;import com.practice.dao.BookDao;
import com.practice.service.BookService;public class BookServiceImpl implements BookService {//删除业务层中使用new的方式创建的dao对象private BookDao bookDao;public void save() {bookDao.save();}//提供对应的set方法public void setBookDao(BookDao bookDao) {this.bookDao = bookDao;}
}

<?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"><!--1.导入spring的坐标spring-context，对应的版本号是5.2.21.RELEASE--><!--2.配置bean--><bean id="bookDao" class="com.practice.dao.impl.BookDaoImpl"/><bean id="bookService" class="com.practice.service.impl.BookServiceImpl"><!--配置service与dao的关系--><!--property标签表示配置当前bean的属性--><!--name属性表示配置哪一个具体的属性--><!--ref属性表示参照哪一个bean--><property name="bookDao" ref="bookDao"/></bean>
</beans>

二、bean的相关操作

2.1bean的配置

2.1.1bean的基础配置

• 1.功能： 定义Spring核心容器管理的对象
• 2.格式：

<beans><bean/><bean></bean>
</beans>

• 3.属性：
• • 3.1id: bean的id，使用容器可以通过id值获取对应的bean,在一个容器中id值唯一
• • 3.2class: bean的类型，即配置的bean的全路径类名

2.1.2bean的别名配置

• 别名配置就是在bean标签中添加一个name属性，这个name属性就是bean的别名，可以有多个别名中间用逗号、空格或分号隔开即可

<?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"><!--1.导入spring的坐标spring-context，对应的版本号是5.2.21.RELEASE--><!--2.配置bean--><bean id="bookDao" class="com.practice.dao.impl.BookDaoImpl"/><!--name起别名--><bean id="bookService" name="service" class="com.practice.service.impl.BookServiceImpl"><!--配置service与dao的关系--><!--property标签表示配置当前bean的属性--><!--name属性表示配置哪一个具体的属性--><!--ref属性表示参照哪一个bean--><property name="bookDao" ref="bookDao"/></bean>
</beans>

package com.practice;import com.practice.dao.BookDao;
import com.practice.service.BookService;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;/*** @Author YJ* @Date 2023/7/25 11:33* Description:*/
public class App {public static void main(String[] args) {//获取IoC容器ApplicationContext act = new ClassPathXmlApplicationContext("applicationContext.xml");//获取bean/*BookDao bookDao = (BookDao) act.getBean("bookDao");bookDao.save();*/BookService bookService = (BookService) act.getBean("service");//用到别名servicebookService.save();}
}

• 若是bean的名称跟配置的不一致会出现NoSuchBeanDefinitionException异常，表示该bean未定义

public class App {public static void main(String[] args) {//获取IoC容器ApplicationContext act = new ClassPathXmlApplicationContext("applicationContext.xml");//获取bean/*BookDao bookDao = (BookDao) act.getBean("bookDao");bookDao.save();*/BookService bookService = (BookService) act.getBean("service1");//用到错误别名service1bookService.save();}
}

2.1.3bean的作用范围配置

• Spring默认配置的bean是一个单列的，即只有一个bean对象，如下所示：

public class AppForScope {public static void main(String[] args) {//获取IoC容器ApplicationContext act = new ClassPathXmlApplicationContext("applicationContext.xml");BookDao bookDao1 = (BookDao) act.getBean("bookDao");BookDao bookDao2 = (BookDao) act.getBean("bookDao");System.out.println(bookDao1);System.out.println(bookDao2);}
}

---

• 我们可以通过配置bean的文件控制是否产生一个对象还是多个对象
• 通过scope属性定义bean的作用范围，可选范围如下：
• • singleton:单例（默认）
• • prototype:非单例

---

---

• 适合交给容器进行管理的bean
• • 表现层对象
• • 业务层对象
• • 数据层对象
• • 工具对象
• 不适合交给容器进行管理的bean
• • 封装实体的域对象

2.2bean的实例化 - - 构造方法

• bean本质上就是对象，创建bean使用构造方法完成

public class BookDaoImpl implements BookDao {private BookDaoImpl() {System.out.println("book dao constructor running...");}public void save() {System.out.println("bookDao save~");}
}

public class App {public static void main(String[] args) {//获取IoC容器ApplicationContext act = new ClassPathXmlApplicationContext("applicationContext.xml");//获取beanBookDao bookDao = (BookDao) act.getBean("bookDao");bookDao.save();}
}

<?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"><!--1.导入spring的坐标spring-context，对应的版本号是5.2.21.RELEASE--><!--2.配置bean--><bean id="bookDao" class="com.practice.dao.impl.BookDaoImpl" scope="prototype"/><!--name起别名--><bean id="bookService" name="service" class="com.practice.service.impl.BookServiceImpl" ><!--配置service与dao的关系--><!--property标签表示配置当前bean的属性--><!--name属性表示配置哪一个具体的属性--><!--ref属性表示参照哪一个bean--><property name="bookDao" ref="bookDao"/></bean>
</beans>

• 表明bean在创建时调用的无参构造方法
• 无参构造方法如果不存在，会抛出BeanCreationException异常

2.3bean的实例化 - - 实例工厂与FactoryBean

<?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"><!--1.导入spring的坐标spring-context，对应的版本号是5.2.21.RELEASE--><!--2.配置bean--><!--方式三：使用实例化工厂实例化bean--><bean id="userFactory" class="com.practice.factory.UserDaoFactory"/><bean id="userDao" factory-bean="userFactory" factory-method="getUserDao"/>
</beans>

public interface UserDao {public void save();
}

public class UserDaoImpl implements UserDao {public void save() {System.out.println("UserDao save...");}
}

public class UserDaoFactory {public UserDao getUserDao(){return new UserDaoImpl();}
}

package com.practice;import com.practice.dao.UserDao;
import com.practice.factory.UserDaoFactory;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;/*** @Author YJ* @Date 2023/7/25 19:09* Description:*/
public class AppForInstanceUser {public static void main(String[] args) {/*//创建实例工厂对象UserDaoFactory userDaoFactory = new UserDaoFactory();UserDao userDao = userDaoFactory.getUserDao();userDao.save();*///获取IoC容器ApplicationContext act = new ClassPathXmlApplicationContext("applicationContext.xml");//获取beanUserDao userDao = (UserDao) act.getBean("userDao");userDao.save();}
}

• 使用FactoryBean实例化bean

package com.practice.factory;import com.practice.dao.UserDao;
import com.practice.dao.impl.UserDaoImpl;
import org.springframework.beans.factory.FactoryBean;/*** @Author YJ* @Date 2023/7/25 19:21* Description:使用FactoryBean实例化bean*/
public class UserDaoFactoryBean implements FactoryBean<UserDao> {public UserDao getObject() throws Exception {//代替原始实例工厂中创建对象的方法return new UserDaoImpl();}public Class<?> getObjectType() {return UserDao.class;}
}

<?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"><!--方式三：使用实例化工厂实例化bean--><bean id="userFactory" class="com.practice.factory.UserDaoFactory"/><bean id="userDao1" factory-bean="userFactory" factory-method="getUserDao"/><!--方式四：使用FactoryBean实例化bean--><bean id="userDao" class="com.practice.factory.UserDaoFactoryBean"/></beans>

• 使用这种方式创建出的bean是单例的
  
• 可在UserDaoFactoryBean中实现方法isSingleton并返回false即可

public boolean isSingleton() {return false;}

2.4bean的生命周期

• 生命周期：从创建到消亡的完整过程
• bean生命周期：bean从创建到消毁的整体过程
• bean生命周期控制：在bean创建后到销毁前做一些事情

package com.practice.dao.impl;import com.practice.dao.BookDao;/*** @Author YJ* @Date 2023/7/25 11:24* Description:*/
public class BookDaoImpl1 implements BookDao {public void save() {System.out.println("bookDao save~");}//表示bean初始化public void init() {System.out.println("init...");}//表示bean销毁前对应操作public void destroy() {System.out.println("destroy...");}
}

<?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"><!--方式三：使用实例化工厂实例化bean--><!--<bean id="userFactory" class="com.practice.factory.UserDaoFactory"/>--><!--<bean id="userDao1" factory-bean="userFactory" factory-method="getUserDao"/>--><!--方式四：使用FactoryBean实例化bean--><!--<bean id="userDao" class="com.practice.factory.UserDaoFactoryBean"/>--><!--配置bean的生命周期--><bean id="bookDao" class="com.practice.dao.impl.BookDaoImpl1" init-method="init" destroy-method="destroy"/>
</beans>

package com.practice;import com.practice.dao.BookDao;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;/*** @Author YJ* @Date 2023/7/25 19:40* Description:*/
public class AppForLifeCycle {public static void main(String[] args) {//获取IoC容器ClassPathXmlApplicationContextact = new ClassPathXmlApplicationContext("applicationContext.xml");//获取beanBookDao bookDao = (BookDao) act.getBean("bookDao");bookDao.save();//关闭容器，才能看到destory方法的执行结果//1.暴力关闭act.close();//2.关闭钩子act.registerShutdownHook();}
}

package com.practice.service.impl;import com.practice.dao.BookDao;
import com.practice.dao.impl.BookDaoImpl1;
import com.practice.service.BookService;
import org.springframework.beans.factory.DisposableBean;
import org.springframework.beans.factory.InitializingBean;/*** @Author YJ* @Date 2023/7/25 11:28* Description:*/
public class BookServiceImpl1 implements BookService, InitializingBean, DisposableBean {private BookDao bookDao;public void save() {System.out.println("bookService save...");bookDao.save();}public void afterPropertiesSet() throws Exception {System.out.println("service init...");}public void destroy() throws Exception {System.out.println("service destroy...");}public void setBookDao(BookDaoImpl1 bookDao) {this.bookDao=bookDao;}
}

package com.practice;import com.practice.dao.BookDao;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;/*** @Author YJ* @Date 2023/7/25 19:40* Description:*/
public class AppForLifeCycle {public static void main(String[] args) {//获取IoC容器ClassPathXmlApplicationContext act = new ClassPathXmlApplicationContext("applicationContext.xml");//获取beanBookDao bookDao = (BookDao) act.getBean("bookDao");bookDao.save();//act.close();act.registerShutdownHook();}
}

<?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"><!--方式三：使用实例化工厂实例化bean--><!--<bean id="userFactory" class="com.practice.factory.UserDaoFactory"/>--><!--<bean id="userDao1" factory-bean="userFactory" factory-method="getUserDao"/>--><!--方式四：使用FactoryBean实例化bean--><!--<bean id="userDao" class="com.practice.factory.UserDaoFactoryBean"/>--><!--配置bean的生命周期--><bean id="bookDao" class="com.practice.dao.impl.BookDaoImpl1" init-method="init" destroy-method="destroy"/><bean id="bookService" class="com.practice.service.impl.BookServiceImpl1"><property name="bookDao" ref="bookDao"/></bean>
</beans>

总结

关于Spring的初步认识我们就学到这里了，关于bean的操作我们有了基本的认识，欢迎各位小伙伴点赞+关注！！！