3、容器：IoC

IoC 是 Inversion of Control 的简写，译为“控制反转”，它不是一门技术，而是一种设计思想，是一个重要的面向对象编程法则，能够指导我们如何设计出松耦合、更优良的程序。

Spring 通过 IoC 容器来管理所有 Java 对象的实例化和初始化，控制对象与对象之间的依赖关系。我们将由 IoC 容器管理的 Java 对象称为 Spring Bean，它与使用关键字 new 创建的 Java 对象没有任何区别。

IoC 容器是 Spring 框架中最重要的核心组件之一，它贯穿了 Spring 从诞生到成长的整个过程。

3.1、IoC容器

3.1.1、控制反转（IoC）

• 控制反转是一种思想。

• 控制反转是为了降低程序耦合度，提高程序扩展力。

• 控制反转，反转的是什么？

• • 将对象的创建权利交出去，交给第三方容器负责。
  • 将对象和对象之间关系的维护权交出去，交给第三方容器负责。

• 控制反转这种思想如何实现呢？

• • DI（Dependency Injection）：依赖注入

3.1.2、依赖注入

DI（Dependency Injection）：依赖注入，依赖注入实现了控制反转的思想。

依赖注入：

• 指Spring创建对象的过程中，将对象依赖属性通过配置进行注入

依赖注入常见的实现方式包括两种：

• 第一种：set注入
• 第二种：构造注入

所以结论是：IOC 就是一种控制反转的思想， 而 DI 是对IoC的一种具体实现。

Bean管理说的是：Bean对象的创建，以及Bean对象中属性的赋值（或者叫做Bean对象之间关系的维护）。

3.1.3、IoC容器在Spring的实现

Spring 的 IoC 容器就是 IoC思想的一个落地的产品实现。IoC容器中管理的组件也叫做 bean。在创建 bean 之前，首先需要创建IoC 容器。Spring 提供了IoC 容器的两种实现方式：

①BeanFactory

这是 IoC 容器的基本实现，是 Spring 内部使用的接口。面向 Spring 本身，不提供给开发人员使用。

②ApplicationContext

BeanFactory 的子接口，提供了更多高级特性。面向 Spring 的使用者，几乎所有场合都使用 ApplicationContext 而不是底层的 BeanFactory。

③ApplicationContext的主要实现类

3.2、基于XML管理Bean

3.2.1、搭建子模块spring6-ioc-xml

①搭建模块

搭建方式如：spring-first

②引入配置文件

引入spring-first模块配置文件：beans.xml、log4j2.xml

③添加依赖

org.springframeworkspring-context6.0.3org.junit.jupiterjunit-jupiter-api5.3.1org.apache.logging.log4jlog4j-core2.19.0org.apache.logging.log4jlog4j-slf4j2-impl2.19.0

④引入java类

引入spring-first模块java及test目录下实体类

package com.atguigu.spring6.bean;public class HelloWorld {public HelloWorld() {System.out.println("无参数构造方法执行");}public void sayHello(){System.out.println("helloworld");}
}

package com.atguigu.spring6.bean;import org.junit.jupiter.api.Test;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;public class HelloWorldTest {private Logger logger = LoggerFactory.getLogger(HelloWorldTest.class);@Testpublic void testHelloWorld(){}
}

3.2.2、实验一：获取bean

配置bean

①方式一：根据id获取

由于 id 属性指定了 bean 的唯一标识，所以根据 bean 标签的 id 属性可以精确获取到一个组件对象。

@Test
public void testHelloWorld(){ApplicationContext ac = new ClassPathXmlApplicationContext("beans.xml");HelloWorld helloworld = (HelloWorld) ac.getBean("helloWorld");helloworld.sayHello();
}

②方式二：根据类型获取

@Test
public void testHelloWorld1(){ApplicationContext ac = new ClassPathXmlApplicationContext("beans.xml");HelloWorld bean = ac.getBean(HelloWorld.class);bean.sayHello();
}

③方式三：根据id和类型

@Test
public void testHelloWorld2(){ApplicationContext ac = new ClassPathXmlApplicationContext("beans.xml");HelloWorld bean = ac.getBean("helloworld", HelloWorld.class);bean.sayHello();
}

④注意的地方

当根据类型获取bean时，要求IOC容器中指定类型的bean有且只能有一个

当IOC容器中一共配置了两个：

根据类型获取时会抛出异常：

org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type ‘com.atguigu.spring6.bean.HelloWorld’ available: expected single matching bean but found 2: helloworldOne,helloworldTwo

此时只能根据id或者id加类型获取

⑤扩展知识

如果组件类实现了接口，根据接口类型可以获取 bean 吗？

可以，前提是bean唯一

如果一个接口有多个实现类，这些实现类都配置了 bean，根据接口类型可以获取 bean 吗？

不行，因为bean不唯一

结论

根据类型来获取bean时，在满足bean唯一性的前提下，其实只是看：『对象 instanceof 指定的类型』的返回结果，只要返回的是true就可以认定为和类型匹配，能够获取到。

java中，instanceof运算符用于判断前面的对象是否是后面的类，或其子类、实现类的实例。如果是返回true，否则返回false。也就是说：用instanceof关键字做判断时， instanceof 操作符的左右操作必须有继承或实现关系

3.2.3、实验二：依赖注入之setter注入

①创建学生类Student

package com.atguigu.spring6.bean;public class Student {private Integer id;private String name;private Integer age;private String sex;public Student() {}public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public Integer getAge() {return age;}public void setAge(Integer age) {this.age = age;}public String getSex() {return sex;}public void setSex(String sex) {this.sex = sex;}@Overridepublic String toString() {return "Student{" +"id=" + id +", name='" + name + '\'' +", age=" + age +", sex='" + sex + '\'' +'}';}}

②配置bean时为属性赋值

spring-di.xml

③测试

@Test
public void testDIBySet(){ApplicationContext ac = new ClassPathXmlApplicationContext("spring-di.xml");Student studentOne = ac.getBean("studentOne", Student.class);System.out.println(studentOne);
}

3.2.4、实验三：依赖注入之构造器注入

①在Student类中添加有参构造

public Student(Integer id, String name, Integer age, String sex) {this.id = id;this.name = name;this.age = age;this.sex = sex;
}

②配置bean

spring-di.xml

注意：

constructor-arg标签还有两个属性可以进一步描述构造器参数：

• index属性：指定参数所在位置的索引（从0开始）
• name属性：指定参数名

③测试

@Test
public void testDIByConstructor(){ApplicationContext ac = new ClassPathXmlApplicationContext("spring-di.xml");Student studentOne = ac.getBean("studentTwo", Student.class);System.out.println(studentOne);
}

通过构造器注入时只会执行有参构造器

3.2.5、实验四：特殊值处理

①字面量赋值

什么是字面量？

int a = 10;

声明一个变量a，初始化为10，此时a就不代表字母a了，而是作为一个变量的名字。当我们引用a的时候，我们实际上拿到的值是10。

而如果a是带引号的：‘a’，那么它现在不是一个变量，它就是代表a这个字母本身，这就是字面量。所以字面量没有引申含义，就是我们看到的这个数据本身。

②null值

注意：

以上写法，为name所赋的值是字符串null

③xml实体

④CDATA节

3.2.6、实验五：为对象类型属性赋值

①创建班级类Clazz

package com.atguigu.spring6.beanpublic class Clazz {private Integer clazzId;private String clazzName;public Integer getClazzId() {return clazzId;}public void setClazzId(Integer clazzId) {this.clazzId = clazzId;}public String getClazzName() {return clazzName;}public void setClazzName(String clazzName) {this.clazzName = clazzName;}@Overridepublic String toString() {return "Clazz{" +"clazzId=" + clazzId +", clazzName='" + clazzName + '\'' +'}';}public Clazz() {}public Clazz(Integer clazzId, String clazzName) {this.clazzId = clazzId;this.clazzName = clazzName;}
}

②修改Student类

在Student类中添加以下代码：

private Clazz clazz;public Clazz getClazz() {return clazz;
}public void setClazz(Clazz clazz) {this.clazz = clazz;
}

方式一：引用外部bean

配置Clazz类型的bean：

为Student中的clazz属性赋值：

错误演示：

如果错把ref属性写成了value属性，会抛出异常： Caused by: java.lang.IllegalStateException: Cannot convert value of type ‘java.lang.String’ to required type ‘com.atguigu.spring6.bean.Clazz’ for property ‘clazz’: no matching editors or conversion strategy found

意思是不能把String类型转换成我们要的Clazz类型，说明我们使用value属性时，Spring只把这个属性看做一个普通的字符串，不会认为这是一个bean的id，更不会根据它去找到bean来赋值

方式二：内部bean

方式三：级联属性赋值

3.2.7、实验六：为数组类型属性赋值

①修改Student类

在Student类中添加以下代码：

private String[] hobbies;public String[] getHobbies() {return hobbies;
}public void setHobbies(String[] hobbies) {this.hobbies = hobbies;
}

②配置bean

抽烟喝酒烫头

3.2.8、实验七：为集合类型属性赋值

①为List集合类型属性赋值

在Clazz类中添加以下代码：

private List students;public List getStudents() {return students;
}public void setStudents(List students) {this.students = students;
}

配置bean：

若为Set集合类型属性赋值，只需要将其中的list标签改为set标签即可

②为Map集合类型属性赋值

创建教师类Teacher：

package com.atguigu.spring6.bean;
public class Teacher {private Integer teacherId;private String teacherName;public Integer getTeacherId() {return teacherId;}public void setTeacherId(Integer teacherId) {this.teacherId = teacherId;}public String getTeacherName() {return teacherName;}public void setTeacherName(String teacherName) {this.teacherName = teacherName;}public Teacher(Integer teacherId, String teacherName) {this.teacherId = teacherId;this.teacherName = teacherName;}public Teacher() {}@Overridepublic String toString() {return "Teacher{" +"teacherId=" + teacherId +", teacherName='" + teacherName + '\'' +'}';}
}

在Student类中添加以下代码：

private Map teacherMap;public Map getTeacherMap() {return teacherMap;
}public void setTeacherMap(Map teacherMap) {this.teacherMap = teacherMap;
}

配置bean：

抽烟喝酒烫头

③引用集合类型的bean

1001010086



抽烟喝酒烫头

使用util:list、util:map标签必须引入相应的命名空间

3.2.9、实验八：p命名空间

引入p命名空间

引入p命名空间后，可以通过以下方式为bean的各个属性赋值

3.2.10、实验九：引入外部属性文件

①加入依赖

 
mysqlmysql-connector-java8.0.30

com.alibabadruid1.2.15

②创建外部属性文件

[外链图片转存失败,源站可能有防盗链机制,建议将图片保存下来直接上传(img-BQVUwjNN-1677994650279)(images/spring6/img010.png)]

jdbc.user=root
jdbc.password=atguigu
jdbc.url=jdbc:mysql://localhost:3306/ssm?serverTimezone=UTC
jdbc.driver=com.mysql.cj.jdbc.Driver

③引入属性文件

引入context 名称空间

注意：在使用 context:property-placeholder 元素加载外包配置文件功能前，首先需要在 XML 配置的一级标签 中添加 context 相关的约束。

④配置bean

⑤测试

@Test
public void testDataSource() throws SQLException {ApplicationContext ac = new ClassPathXmlApplicationContext("spring-datasource.xml");DataSource dataSource = ac.getBean(DataSource.class);Connection connection = dataSource.getConnection();System.out.println(connection);
}

3.2.11、实验十：bean的作用域

①概念

在Spring中可以通过配置bean标签的scope属性来指定bean的作用域范围，各取值含义参加下表：

如果是在WebApplicationContext环境下还会有另外几个作用域（但不常用）：

②创建类User

package com.atguigu.spring6.bean;
public class User {private Integer id;private String username;private String password;private Integer age;public User() {}public User(Integer id, String username, String password, Integer age) {this.id = id;this.username = username;this.password = password;this.age = age;}public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public String getUsername() {return username;}public void setUsername(String username) {this.username = username;}public String getPassword() {return password;}public void setPassword(String password) {this.password = password;}public Integer getAge() {return age;}public void setAge(Integer age) {this.age = age;}@Overridepublic String toString() {return "User{" +"id=" + id +", username='" + username + '\'' +", password='" + password + '\'' +", age=" + age +'}';}
}

③配置bean

④测试

@Test
public void testBeanScope(){ApplicationContext ac = new ClassPathXmlApplicationContext("spring-scope.xml");User user1 = ac.getBean(User.class);User user2 = ac.getBean(User.class);System.out.println(user1==user2);
}

通过测试可以看出，scope="prototype"得到的两个bean不是同一个bean

3.2.12、实验十一：bean生命周期

①具体的生命周期过程

• bean对象创建（调用无参构造器）

• 给bean对象设置属性

• bean的前置处理器（初始化之前）

• bean对象初始化（需在配置bean时指定初始化方法）

• bean的后置处理器（初始化之后）

• bean对象就绪可以使用

• bean对象销毁（需在配置bean时指定销毁方法）

• IOC容器关闭

②修改类User

public class User {private Integer id;private String username;private String password;private Integer age;public User() {System.out.println("生命周期：1、创建对象");}public User(Integer id, String username, String password, Integer age) {this.id = id;this.username = username;this.password = password;this.age = age;}public Integer getId() {return id;}public void setId(Integer id) {System.out.println("生命周期：2、依赖注入");this.id = id;}public String getUsername() {return username;}public void setUsername(String username) {this.username = username;}public String getPassword() {return password;}public void setPassword(String password) {this.password = password;}public Integer getAge() {return age;}public void setAge(Integer age) {this.age = age;}public void initMethod(){System.out.println("生命周期：3、初始化");}public void destroyMethod(){System.out.println("生命周期：5、销毁");}@Overridepublic String toString() {return "User{" +"id=" + id +", username='" + username + '\'' +", password='" + password + '\'' +", age=" + age +'}';}
}

注意其中的initMethod()和destroyMethod()，可以通过配置bean指定为初始化和销毁的方法

③配置bean

④测试

@Test
public void testLife(){ClassPathXmlApplicationContext ac = new ClassPathXmlApplicationContext("spring-lifecycle.xml");User bean = ac.getBean(User.class);System.out.println("生命周期：4、通过IOC容器获取bean并使用");ac.close();
}

⑤bean的后置处理器

bean的后置处理器会在生命周期的初始化前后添加额外的操作，需要实现BeanPostProcessor接口，且配置到IOC容器中，需要注意的是，bean后置处理器不是单独针对某一个bean生效，而是针对IOC容器中所有bean都会执行

创建bean的后置处理器：

package com.atguigu.spring6.process;import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;public class MyBeanProcessor implements BeanPostProcessor {@Overridepublic Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {System.out.println("☆☆☆" + beanName + " = " + bean);return bean;}@Overridepublic Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {System.out.println("★★★" + beanName + " = " + bean);return bean;}
}

在IOC容器中配置后置处理器：

注意此处如果是这样子写，就只会执行有参构造器，不会执行无参构造器

3.2.13、实验十二：FactoryBean

①简介

FactoryBean是Spring提供的一种整合第三方框架的常用机制。和普通的bean不同，配置一个FactoryBean类型的bean，在获取bean的时候得到的并不是class属性中配置的这个类的对象，而是getObject()方法的返回值。通过这种机制，Spring可以帮我们把复杂组件创建的详细过程和繁琐细节都屏蔽起来，只把最简洁的使用界面展示给我们。

将来我们整合Mybatis时，Spring就是通过FactoryBean机制来帮我们创建SqlSessionFactory对象的。

/** Copyright 2002-2020 the original author or authors.** Licensed under the Apache License, Version 2.0 (the "License");* you may not use this file except in compliance with the License.* You may obtain a copy of the License at**      https://www.apache.org/licenses/LICENSE-2.0** Unless required by applicable law or agreed to in writing, software* distributed under the License is distributed on an "AS IS" BASIS,* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.* See the License for the specific language governing permissions and* limitations under the License.*/
package org.springframework.beans.factory;import org.springframework.lang.Nullable;/*** Interface to be implemented by objects used within a {@link BeanFactory} which* are themselves factories for individual objects. If a bean implements this* interface, it is used as a factory for an object to expose, not directly as a* bean instance that will be exposed itself.** 
NB: A bean that implements this interface cannot be used as a normal bean.* A FactoryBean is defined in a bean style, but the object exposed for bean* references ({@link #getObject()}) is always the object that it creates.** 
FactoryBeans can support singletons and prototypes, and can either create* objects lazily on demand or eagerly on startup. The {@link SmartFactoryBean}* interface allows for exposing more fine-grained behavioral metadata.** 
This interface is heavily used within the framework itself, for example for* the AOP {@link org.springframework.aop.framework.ProxyFactoryBean} or the* {@link org.springframework.jndi.JndiObjectFactoryBean}. It can be used for* custom components as well; however, this is only common for infrastructure code.** 
{@code FactoryBean} is a programmatic contract. Implementations are not* supposed to rely on annotation-driven injection or other reflective facilities.* {@link #getObjectType()} {@link #getObject()} invocations may arrive early in the* bootstrap process, even ahead of any post-processor setup. If you need access to* other beans, implement {@link BeanFactoryAware} and obtain them programmatically.** 
The container is only responsible for managing the lifecycle of the FactoryBean* instance, not the lifecycle of the objects created by the FactoryBean. Therefore,* a destroy method on an exposed bean object (such as {@link java.io.Closeable#close()}* will not be called automatically. Instead, a FactoryBean should implement* {@link DisposableBean} and delegate any such close call to the underlying object.** 
Finally, FactoryBean objects participate in the containing BeanFactory's* synchronization of bean creation. There is usually no need for internal* synchronization other than for purposes of lazy initialization within the* FactoryBean itself (or the like).** @author Rod Johnson* @author Juergen Hoeller* @since 08.03.2003* @param  the bean type* @see org.springframework.beans.factory.BeanFactory* @see org.springframework.aop.framework.ProxyFactoryBean* @see org.springframework.jndi.JndiObjectFactoryBean*/
public interface FactoryBean {/*** The name of an attribute that can be* {@link org.springframework.core.AttributeAccessor#setAttribute set} on a* {@link org.springframework.beans.factory.config.BeanDefinition} so that* factory beans can signal their object type when it can't be deduced from* the factory bean class.* @since 5.2*/String OBJECT_TYPE_ATTRIBUTE = "factoryBeanObjectType";/*** Return an instance (possibly shared or independent) of the object* managed by this factory.* 
As with a {@link BeanFactory}, this allows support for both the* Singleton and Prototype design pattern.* 
If this FactoryBean is not fully initialized yet at the time of* the call (for example because it is involved in a circular reference),* throw a corresponding {@link FactoryBeanNotInitializedException}.* 
As of Spring 2.0, FactoryBeans are allowed to return {@code null}* objects. The factory will consider this as normal value to be used; it* will not throw a FactoryBeanNotInitializedException in this case anymore.* FactoryBean implementations are encouraged to throw* FactoryBeanNotInitializedException themselves now, as appropriate.* @return an instance of the bean (can be {@code null})* @throws Exception in case of creation errors* @see FactoryBeanNotInitializedException*/@NullableT getObject() throws Exception;/*** Return the type of object that this FactoryBean creates,* or {@code null} if not known in advance.* 
This allows one to check for specific types of beans without* instantiating objects, for example on autowiring.* 
In the case of implementations that are creating a singleton object,* this method should try to avoid singleton creation as far as possible;* it should rather estimate the type in advance.* For prototypes, returning a meaningful type here is advisable too.* 
This method can be called before this FactoryBean has* been fully initialized. It must not rely on state created during* initialization; of course, it can still use such state if available.* 
NOTE: Autowiring will simply ignore FactoryBeans that return* {@code null} here. Therefore it is highly recommended to implement* this method properly, using the current state of the FactoryBean.* @return the type of object that this FactoryBean creates,* or {@code null} if not known at the time of the call* @see ListableBeanFactory#getBeansOfType*/@NullableClass getObjectType();/*** Is the object managed by this factory a singleton? That is,* will {@link #getObject()} always return the same object* (a reference that can be cached)?* 
NOTE: If a FactoryBean indicates to hold a singleton object,* the object returned from {@code getObject()} might get cached* by the owning BeanFactory. Hence, do not return {@code true}* unless the FactoryBean always exposes the same reference.* 
The singleton status of the FactoryBean itself will generally* be provided by the owning BeanFactory; usually, it has to be* defined as singleton there.* 
NOTE: This method returning {@code false} does not* necessarily indicate that returned objects are independent instances.* An implementation of the extended {@link SmartFactoryBean} interface* may explicitly indicate independent instances through its* {@link SmartFactoryBean#isPrototype()} method. Plain {@link FactoryBean}* implementations which do not implement this extended interface are* simply assumed to always return independent instances if the* {@code isSingleton()} implementation returns {@code false}.* 
The default implementation returns {@code true}, since a* {@code FactoryBean} typically manages a singleton instance.* @return whether the exposed object is a singleton* @see #getObject()* @see SmartFactoryBean#isPrototype()*/default boolean isSingleton() {return true;}
}

②创建类UserFactoryBean

package com.atguigu.spring6.bean;
public class UserFactoryBean implements FactoryBean {@Overridepublic User getObject() throws Exception {return new User();}@Overridepublic Class getObjectType() {return User.class;}
}

③配置bean

④测试

@Test
public void testUserFactoryBean(){//获取IOC容器ApplicationContext ac = new ClassPathXmlApplicationContext("spring-factorybean.xml");User user = (User) ac.getBean("user");System.out.println(user);
}

3.2.14、实验十三：基于xml自动装配

自动装配：

根据指定的策略，在IOC容器中匹配某一个bean，自动为指定的bean中所依赖的类类型或接口类型属性赋值

①场景模拟

创建类UserController

package com.atguigu.spring6.autowire.controller
public class UserController {private UserService userService;public void setUserService(UserService userService) {this.userService = userService;}public void saveUser(){userService.saveUser();}}

创建接口UserService

package com.atguigu.spring6.autowire.service
public interface UserService {void saveUser();}

创建类UserServiceImpl实现接口UserService

package com.atguigu.spring6.autowire.service.impl
public class UserServiceImpl implements UserService {private UserDao userDao;public void setUserDao(UserDao userDao) {this.userDao = userDao;}@Overridepublic void saveUser() {userDao.saveUser();}}

创建接口UserDao

package com.atguigu.spring6.autowire.dao
public interface UserDao {void saveUser();}

创建类UserDaoImpl实现接口UserDao

package com.atguigu.spring6.autowire.dao.impl
public class UserDaoImpl implements UserDao {@Overridepublic void saveUser() {System.out.println("保存成功");}}

②配置bean

使用bean标签的autowire属性设置自动装配效果

自动装配方式：byType

byType：根据类型匹配IOC容器中的某个兼容类型的bean，为属性自动赋值

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

自动装配方式：byName

byName：将自动装配的属性的属性名，作为bean的id在IOC容器中匹配相对应的bean进行赋值

③测试

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

本文章参考B站 尚硅谷Spring零基础视频教程，2023版spring6入门到精通，仅供个人学习使用，部分内容为本人自己见解，与尚硅谷无关。