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.springframeworkgroupId>
     <artifactId>spring-contextartifactId>
     <version>5.2.21.RELEASEversion>
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

<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="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;
    }
}

<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="bookDao" class="com.practice.dao.impl.BookDaoImpl"/>
    <bean id="bookService" class="com.practice.service.impl.BookServiceImpl">
        
        
        
        
        <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

<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="bookDao" class="com.practice.dao.impl.BookDaoImpl"/>
    
    <bean id="bookService" name="service" class="com.practice.service.impl.BookServiceImpl">
        
        
        
        
        <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service
        bookService.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service1
        bookService.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bean
        BookDao bookDao = (BookDao) act.getBean("bookDao");
        bookDao.save();
        

    }
}

<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="bookDao" class="com.practice.dao.impl.BookDaoImpl" scope="prototype"/>
    
    <bean id="bookService" name="service" class="com.practice.service.impl.BookServiceImpl" >
        
        
        
        
        <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

<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="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bean
        UserDao 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;
    }
}

<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="userFactory" class="com.practice.factory.UserDaoFactory"/>
    <bean id="userDao1" factory-bean="userFactory" factory-method="getUserDao"/>
    
    <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...");
    }
}

<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="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bean
        BookDao 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bean
        BookDao bookDao = (BookDao) act.getBean("bookDao");
        bookDao.save();
        //act.close();
        act.registerShutdownHook();

    }
}

<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="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！！！