Spring容器——基于XML注入

1. 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

1.1 IOC容器

1.1.1 控制反转

• 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

1.1.2 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）。

1.1.3 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

类型名	简介
ClassPathXmlApplicationContext	通过读取类路径下的 XML 格式的配置文件创建 IOC 容器对象
FileSystemXmlApplicationContext	通过文件系统路径读取 XML 格式的配置文件创建 IOC 容器对象
ConfigurableApplicationContext	ApplicationContext 的子接口，包含一些扩展方法 refresh() 和 close() ，让 ApplicationContext 具有启动、关闭和刷新上下文的能力。
WebApplicationContext	专门为 Web 应用准备，基于 Web 环境创建 IOC 容器对象，并将对象引入存入 ServletContext 域中。

3.2 基于XML管理bean

3.2.1、搭建子模块spring6-ioc-xml

添加依赖

<dependencies><!--spring context依赖--><!--当你引入Spring Context依赖之后，表示将Spring的基础依赖引入了--><dependency><groupId>org.springframework</groupId><artifactId>spring-context</artifactId><version>6.0.3</version></dependency><!--junit5测试--><dependency><groupId>org.junit.jupiter</groupId><artifactId>junit-jupiter-api</artifactId><version>5.3.1</version></dependency><!--log4j2的依赖--><dependency><groupId>org.apache.logging.log4j</groupId><artifactId>log4j-core</artifactId><version>2.19.0</version></dependency><dependency><groupId>org.apache.logging.log4j</groupId><artifactId>log4j-slf4j2-impl</artifactId><version>2.19.0</version></dependency>
</dependencies>

3.2.2 获取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。上个实验中我们使用的就是这种
2. 方式二：根据类型获取

@Test
public void testHelloWorld1(){ApplicationContext ac = new ClassPathXmlApplicationContext("beans.xml");//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();
}

3.2.3 依赖注入之setter注入

1. 创建User类

package com.gdhd.domain;public class User {private String name;private Integer age;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;}@Overridepublic String toString() {return "User{" +"name='" + name + '\'' +", age=" + age +'}';}
}

2. 配置bean时为属性赋值

<bean id="user" class="com.gdhd.domin.User"><!-- property标签：通过组件类的setXxx()方法给组件对象设置属性 --><!-- name属性：指定属性名（这个属性名是getXxx()、setXxx()方法定义的，和成员变量无关） --><!-- value属性：指定属性值 --><property name="name" value="张三"></property><property name="age" value="23"></property>
</bean>

3. 测试

public class UserTest {@Testpublic void name(){ApplicationContext ac=new ClassPathXmlApplicationContext ("bean.xml");User user = (User) ac.getBean("user");System.out.println(user);}
}
}

3.2.4 依赖注入之构造器注入

1. 在User类添加有参构造

 public User(String name, Integer age) {this.name = name;this.age = age;}

2. 配置Bean

    <bean id="user" class="com.gdhd.domain.User"><!-- constructor标签：通过组件类的构造器方法给组件对象设置属性 --><!--valus:赋值，name:指定参数名，index：指定参数所在位置的索引(从0开始)--><constructor-arg value="小道"></constructor-arg><constructor-arg value="30"></constructor-arg></bean>

测试

public class UserTest {@Testpublic void name(){ApplicationContext ac=new ClassPathXmlApplicationContext ("bean.xml");User user = (User) ac.getBean("user");System.out.println(user);}
}

3.2.5 特殊值处理

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

<!-- 使用value属性给bean的属性赋值时，Spring会把value属性的值看做字面量 -->
<property name="name" value="张三"/>

2. null值

<property name="name"><null />
</property>

3. xml实体

<!-- 小于号在XML文档中用来定义标签的开始，不能随便使用 -->
<!-- 解决方案一：使用XML实体来代替 -->
<property name="expression" value="a &lt; b"/>

4. CDATA节

<property name="expression"><!-- 解决方案二：使用CDATA节 --><!-- CDATA中的C代表Character，是文本、字符的含义，CDATA就表示纯文本数据 --><!-- XML解析器看到CDATA节就知道这里是纯文本，就不会当作XML标签或属性来解析 --><!-- 所以CDATA节中写什么符号都随意 --><value><![CDATA[a < b]]></value>
</property

3.2.6 为对象属性赋值

1. 创建Dog类

package com.gdhd.domain;public class Dog {private String name;private  Integer age;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;}@Overridepublic String toString() {return "Dog{" +"name='" + name + '\'' +", age=" + age +'}';}public Dog(String name, Integer age) {this.name = name;this.age = age;}public Dog() {}}

2. 修改User类

 private Dog dog;public String getName() {return name;}public Dog getDog() {return dog;}public void setDog(Dog dog) {this.dog = dog;}

方式一：引用外部的bean
配置Dog类的bean

 <bean id="dog" class="com.gdhd.domain.Dog"><property name="name" value="旺财"></property><property name="age" value="16"></property></bean>

为User中的dog属性赋值

  <property name="name" value="小道"></property><property name="age" value="15"></property><!-- ref属性：引用IOC容器中某个bean的id，将所对应的bean为属性赋值 --><property name="dog" ref="dog"></property>

方式二：内部bean

 <property name="name" value="小道"></property><property name="age" value="15"></property><!-- 在一个bean中再声明一个bean就是内部bean --><!-- 内部bean只能用于给属性赋值，不能在外部通过IOC容器获取，因此可以省略id属性 --><property name="dog" ><bean id="dog" class="com.gdhd.domain.Dog"><property name="name" value="旺财"></property><property name="age" value="16"></property></bean></property>

方式三：级联属性赋值

    <bean id="user" class="com.gdhd.domain.User"><property name="name" value="小道"></property><property name="age" value="15"></property><property name="dog" ref="dogOne"></property><property name="dog.name" value="旺财"></property><property name="dog.age" value="145"></property><!--        <constructor-arg name="age" value="15"></constructor-arg>-->
<!--        <constructor-arg name="name" value="30"></constructor-arg>--></bean><bean id="dogOne" class="com.gdhd.domain.Dog"></bean>

3.2.7 为数组类型属性赋值

修改User类

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

配置Bean

   <property name="hobbies" ><array><value>喝酒</value><value>看书</value></array></property>

3.2.8 为集合类型属性赋值

为List集合类型属性赋值

修改User类

    private List<Dog> dogs;public List<Dog> getDogs() {return dogs;}public void setDogs(List<Dog> dogs) {this.dogs = dogs;}

配置bean

   <property name="dogs"><list><ref bean="dogsOne"></ref><ref bean="dogsTwo"></ref><ref bean="dogsThree"></ref></list></property>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

为Map集合类型属性赋值

创建教师类Teacher

package com.gdhd.domain;public class Teacher {private Integer teachId;private String teachName;public Integer getTeachId() {return teachId;}public void setTeachId(Integer teachId) {this.teachId = teachId;}public String getTeachName() {return teachName;}public void setTeachName(String teachName) {this.teachName = teachName;}@Overridepublic String toString() {return "Teacher{" +"teachId=" + teachId +", teachName='" + teachName + '\'' +'}';}
}

创建Student类

package com.gdhd.domain;import java.util.Map;public class Student {private String name;private Integer age;private Map<String,Teacher> teacherMap;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 Map<String, Teacher> getTeacherMap() {return teacherMap;}public void setTeacherMap(Map<String, Teacher> teacherMap) {this.teacherMap = teacherMap;}@Overridepublic String toString() {return "Student{" +"name='" + name + '\'' +", age=" + age +", teacherMap=" + teacherMap +'}';}
}

配置bean

<bean id="teacherOne" class="com.gdhd.domain.Teacher"><property name="teachId" value="1"></property><property name="teachName" value="语文老师"></property></bean><bean id="teacherFirst" class="com.gdhd.domain.Teacher"><property name="teachId" value="1"></property><property name="teachName" value="数学老师"></property></bean><bean id="student" class="com.gdhd.domain.Student"><property name="name" value="小王"></property><property name="age" value="24"></property><property name="teacherMap" ><map><entry><key><value>1001</value></key><ref bean="teacherOne"></ref></entry><entry><key><value>1002</value></key><ref bean="teacherFirst"></ref></entry></map></property></bean>

引用集合类型的bean

创建Lesson类

package com.gdhd.domain;public class Lesson {private String LessonName;public String getLessonName() {return LessonName;}public void setLessonName(String lesson) {LessonName = lesson;}@Overridepublic String toString() {return "Lesson{" +"Lesson='" + LessonName + '\'' +'}';}
}

修改Student类

private List<Lesson> lessons;public List<Lesson> getLessons() {return lessons;}public void setLessons(List<Lesson> lessons) {this.lessons = lessons;}

引用命名空间

使用util:list、util:map标签必须引入相应的命名空间
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xmlns:util="http://www.springframework.org/schema/util"xsi:schemaLocation="http://www.springframework.org/schema/utilhttp://www.springframework.org/schema/util/spring-util.xsdhttp://www.springframework.org/schema/beanshttp://www.springframework.org/schema/beans/spring-beans.xsd">

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"xmlns:util="http://www.springframework.org/schema/util"xsi:schemaLocation="http://www.springframework.org/schema/utilhttp://www.springframework.org/schema/util/spring-util.xsdhttp://www.springframework.org/schema/beanshttp://www.springframework.org/schema/beans/spring-beans.xsd">
<!--    1 创建三个对象-->
<!--    2 注入普通类型属性-->
<!--    3 使用util:类型 定义-->
<!--    4 在学生bean引入util:类型定义bean，完成list、map类型属性注入-->
<!--    list属性注入--><util:list id="lesson"><ref bean="lessonOne"></ref><ref bean="lessonTow"></ref></util:list><bean id="lessonOne" class="com.gdhd.domain.Lesson"><property name="lessonName" value="java开发"></property></bean><bean id="lessonTow" class="com.gdhd.domain.Lesson"><property name="lessonName" value="计算机网络"></property></bean>
<!--    map类型属性注入--><util:map id="map"><entry><key><value>1001</value></key><ref bean="TeacherOne"></ref></entry><entry><key><value>1002</value></key><ref bean="TeacherTow"></ref></entry></util:map><bean id="TeacherOne" class="com.gdhd.domain.Teacher"><property name="teachId" value="1001"></property><property name="teachName" value="王城老师"></property></bean><bean id="TeacherTow" class="com.gdhd.domain.Teacher"><property name="teachId" value="1001"></property><property name="teachName" value="王城老师"></property></bean><bean id="student" class="com.gdhd.domain.Student"><property name="name" value="小王"></property><property name="age" value="12"></property><property name="lessons" ref="lesson"></property><property name="teacherMap" ref="map"></property></bean>
</beans>

3.2.9 引入外部属性文件

1. 加入依赖

 <!-- MySQL驱动 -->
<dependency><groupId>mysql</groupId><artifactId>mysql-connector-java</artifactId><version>8.0.30</version>
</dependency><!-- 数据源 -->
<dependency><groupId>com.alibaba</groupId><artifactId>druid</artifactId><version>1.2.15</version>
</dependency

2. 创建外部属性文件
   

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

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xmlns:context="http://www.springframework.org/schema/context"xsi:schemaLocation="http://www.springframework.org/schema/beanshttp://www.springframework.org/schema/beans/spring-beans.xsdhttp://www.springframework.org/schema/contexthttp://www.springframework.org/schema/context/spring-context.xsd"></beans>

<!-- 引入外部属性文件 -->
<context:property-placeholder location="classpath:jdbc.properties"/>

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 <beans> 中添加 context 相关的约束。

4. 配置bean

<bean id="druidDataSource" class="com.alibaba.druid.pool.DruidDataSource"><property name="url" value="${jdbc.url}"/><property name="driverClassName" value="${jdbc.driver}"/><property name="username" value="${jdbc.user}"/><property name="password" value="${jdbc.password}"/>
</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);
}

3.2.10 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，取值含义参照下表

取值	含义	创建对象的时机
singleton（默认）	在IOC容器中，这个bean的对象始终为单实例	IOC容器初始化时
prototype	这个bean在IOC容器中有多个实例	获取bean时

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

取值	含义
request	在一个请求范围内有效
session	在一个会话范围内有效
创建User类

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 +'}';}
}

配置Bean

<!-- scope属性：取值singleton（默认值），bean在IOC容器中只有一个实例，IOC容器初始化时创建对象 -->
<!-- scope属性：取值prototype，bean在IOC容器中可以有多个实例，getBean()时创建对象 -->
<bean class="com.atguigu.spring6.bean.User" scope="prototype"></bean>

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);
}

3.2.11 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的后置处理器（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User类

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 +'}';}
}

3. 配置bean

<!-- 使用init-method属性指定初始化方法 -->
<!-- 使用destroy-method属性指定销毁方法 -->
<bean class="com.atguigu.spring6.bean.User" scope="prototype" init-method="initMethod" destroy-method="destroyMethod"><property name="id" value="1001"></property><property name="username" value="admin"></property><property name="password" value="123456"></property><property name="age" value="23"></property>
</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();
}

5. bean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;
//实现BeanPostProcessor接口
public class MyBeanProcessor implements BeanPostProcessor {//在初始化之前执行@Overridepublic Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {System.out.println("☆☆☆" + beanName + " = " + bean);return bean;}//在初始化之后执行@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

<!-- bean的后置处理器要放入IOC容器才能生效 -->
<bean id="myBeanProcessor" class="com.atguigu.spring6.process.MyBeanProcessor"/>

3.2.13 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.** <p><b>NB: A bean that implements this interface cannot be used as a normal bean.</b>* A FactoryBean is defined in a bean style, but the object exposed for bean* references ({@link #getObject()}) is always the object that it creates.** <p>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.** <p>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.** <p><b>{@code FactoryBean} is a programmatic contract. Implementations are not* supposed to rely on annotation-driven injection or other reflective facilities.</b>* {@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.** <p><b>The container is only responsible for managing the lifecycle of the FactoryBean* instance, not the lifecycle of the objects created by the FactoryBean.</b> Therefore,* a destroy method on an exposed bean object (such as {@link java.io.Closeable#close()}* will <i>not</i> be called automatically. Instead, a FactoryBean should implement* {@link DisposableBean} and delegate any such close call to the underlying object.** <p>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 <T> the bean type* @see org.springframework.beans.factory.BeanFactory* @see org.springframework.aop.framework.ProxyFactoryBean* @see org.springframework.jndi.JndiObjectFactoryBean*/
public interface FactoryBean<T> {/*** 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.* <p>As with a {@link BeanFactory}, this allows support for both the* Singleton and Prototype design pattern.* <p>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}.* <p>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.* <p>This allows one to check for specific types of beans without* instantiating objects, for example on autowiring.* <p>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.* <p>This method can be called <i>before</i> 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.* <p><b>NOTE:</b> 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)?* <p><b>NOTE:</b> 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.* <p>The singleton status of the FactoryBean itself will generally* be provided by the owning BeanFactory; usually, it has to be* defined as singleton there.* <p><b>NOTE:</b> 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}.* <p>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

public class UserFactoryBean implements FactoryBean<User> {@Overridepublic User getObject() throws Exception {return new User();}@Overridepublic Class<?> getObjectType() {return User.class;}
}

3. 配置bean

<bean id="user" class="com.atguigu.spring6.bean.UserFactoryBean"></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 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. 创建模拟
   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

<bean id="userController" class="com.atguigu.spring6.autowire.controller.UserController" autowire="byType"></bean><bean id="userService" class="com.atguigu.spring6.autowire.service.impl.UserServiceImpl" autowire="byType"></bean><bean id="userDao" class="com.atguigu.spring6.autowire.dao.impl.UserDaoImpl"></bean>

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

<bean id="userController" class="com.atguigu.spring6.autowire.controller.UserController" autowire="byName"></bean><bean id="userService" class="com.atguigu.spring6.autowire.service.impl.UserServiceImpl" autowire="byName"></bean>
<bean id="userServiceImpl" class="com.atguigu.spring6.autowire.service.impl.UserServiceImpl" autowire="byName"></bean><bean id="userDao" class="com.atguigu.spring6.autowire.dao.impl.UserDaoImpl"></bean>
<bean id="userDaoImpl" class="com.atguigu.spring6.autowire.dao.impl.UserDaoImpl"></bean>

测试

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