Spring IOC基于XML和注解管理Bean（二）

Spring IOC基于XML和注解管理Bean（一）

文章目录

2.9、实验八：p命名空间

引入p命名空间

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

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

<beanid="studentSix"class="org.example.bean.Student"p:id="1006"p:name="小明"p:clazz-ref="clazzOne"p:teacherMap-ref="teacherMap"></bean>

2.10、实验九：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

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jdbc.user=root
jdbc.password=123456
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"?><beansxmlns="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/beans
       http://www.springframework.org/schema/beans/spring-beans.xsd
       http://www.springframework.org/schema/context
       http://www.springframework.org/schema/context/spring-context.xsd"></beans>

<!-- 引入外部属性文件 --><context:property-placeholderlocation="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

<beanid="druidDataSource"class="com.alibaba.druid.pool.DruidDataSource"><propertyname="url"value="${jdbc.url}"/><propertyname="driverClassName"value="${jdbc.driver}"/><propertyname="username"value="${jdbc.user}"/><propertyname="password"value="${jdbc.password}"/></bean>

⑤测试

@TestpublicvoidtestDataSource()throwsSQLException{ApplicationContext ac =newClassPathXmlApplicationContext("spring-datasource.xml");DataSource dataSource = ac.getBean(DataSource.class);Connection connection = dataSource.getConnection();System.out.println(connection);}

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：
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
②创建类User

packageorg.example.bean;publicclassUser{privateInteger id;privateString username;privateString password;privateInteger age;publicUser(){}publicUser(Integer id,String username,String password,Integer age){this.id = id;this.username = username;this.password = password;this.age = age;}publicIntegergetId(){return id;}publicvoidsetId(Integer id){this.id = id;}publicStringgetUsername(){return username;}publicvoidsetUsername(String username){this.username = username;}publicStringgetPassword(){return password;}publicvoidsetPassword(String password){this.password = password;}publicIntegergetAge(){return age;}publicvoidsetAge(Integer age){this.age = age;}@OverridepublicStringtoString(){return"User{"+"id="+ id +", username='"+ username +'\''+", password='"+ password +'\''+", age="+ age +'}';}}

③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 --><beanclass="org.example.bean.User"scope="prototype"></bean>

④测试

@TestpublicvoidtestBeanScope(){ApplicationContext ac =newClassPathXmlApplicationContext("spring-scope.xml");User user1 = ac.getBean(User.class);User user2 = ac.getBean(User.class);System.out.println(user1==user2);}

2.12、实验十一：bean生命周期

①具体的生命周期过程

• 1、bean对象创建（调用无参构造器）
• 2、给bean对象设置属性
• 3、bean的后置处理器（初始化之前）
• 4、bean对象初始化（需在配置bean时指定初始化方法）
• 5、bean的后置处理器（初始化之后）
• 6、bean对象就绪可以使用
• 7、bean对象销毁（需在配置bean时指定销毁方法）
• 8、IOC容器关闭

②修改类User

publicclassUser{privateInteger id;privateString username;privateString password;privateInteger age;publicUser(){System.out.println("生命周期：1、创建对象");}publicUser(Integer id,String username,String password,Integer age){this.id = id;this.username = username;this.password = password;this.age = age;}publicIntegergetId(){return id;}publicvoidsetId(Integer id){System.out.println("生命周期：2、依赖注入");this.id = id;}publicStringgetUsername(){return username;}publicvoidsetUsername(String username){this.username = username;}publicStringgetPassword(){return password;}publicvoidsetPassword(String password){this.password = password;}publicIntegergetAge(){return age;}publicvoidsetAge(Integer age){this.age = age;}publicvoidinitMethod(){System.out.println("生命周期：3、初始化");}publicvoiddestroyMethod(){System.out.println("生命周期：5、销毁");}@OverridepublicStringtoString(){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

<!-- 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 --><beanclass="org.example.bean.User"scope="prototype"init-method="initMethod"destroy-method="destroyMethod"><propertyname="id"value="1001"></property><propertyname="username"value="admin"></property><propertyname="password"value="123456"></property><propertyname="age"value="23"></property></bean>

④测试

@TestpublicvoidtestLife(){ClassPathXmlApplicationContext ac =newClassPathXmlApplicationContext("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：

packageorg.example.process;importorg.springframework.beans.BeansException;importorg.springframework.beans.factory.config.BeanPostProcessor;publicclassMyBeanProcessorimplementsBeanPostProcessor{@OverridepublicObjectpostProcessBeforeInitialization(Object bean,String beanName)throwsBeansException{System.out.println("☆☆☆"+ beanName +" = "+ bean);return bean;}@OverridepublicObjectpostProcessAfterInitialization(Object bean,String beanName)throwsBeansException{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 --><beanid="myBeanProcessor"class="org.example.process.MyBeanProcessor"/>

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。

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.
 */packageorg.springframework.beans.factory;importorg.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
 */publicinterfaceFactoryBean<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
     */@NullableTgetObject()throwsException;/**
     * 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()
     */defaultbooleanisSingleton(){returntrue;}}

②创建类UserFactoryBean

packageorg.example.bean;publicclassUserFactoryBeanimplementsFactoryBean<User>{@OverridepublicUsergetObject()throwsException{returnnewUser();}@OverridepublicClass<?>getObjectType(){returnUser.class;}}

③配置bean

<beanid="user"class="org.example.bean.UserFactoryBean"></bean>

④测试

@TestpublicvoidtestUserFactoryBean(){//获取IOC容器ApplicationContext ac =newClassPathXmlApplicationContext("spring-factorybean.xml");User user =(User) ac.getBean("user");System.out.println(user);}

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

packageorg.example.autowire.controller;publicclassUserController{privateUserService userService;publicvoidsetUserService(UserService userService){this.userService = userService;}publicvoidsaveUser(){
        userService.saveUser();}}

创建接口UserService

packageorg.example.autowire.service;publicinterfaceUserService{voidsaveUser();}

创建类UserServiceImpl实现接口UserService

packageorg.example.autowire.service.impl;publicclassUserServiceImplimplementsUserService{privateUserDao userDao;publicvoidsetUserDao(UserDao userDao){this.userDao = userDao;}@OverridepublicvoidsaveUser(){
        userDao.saveUser();}}

创建接口UserDao

packageorg.example.autowire.dao;publicinterfaceUserDao{voidsaveUser();}

创建类UserDaoImpl实现接口UserDao

packageorg.example.autowire.dao.impl;publicclassUserDaoImplimplementsUserDao{@OverridepublicvoidsaveUser(){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

<beanid="userController"class="org.example.autowire.controller.UserController"autowire="byType"></bean><beanid="userService"class="org.example.autowire.service.impl.UserServiceImpl"autowire="byType"></bean><beanid="userDao"class="org.example.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

<beanid="userController"class="org.example.autowire.controller.UserController"autowire="byName"></bean><beanid="userService"class="org.example.autowire.service.impl.UserServiceImpl"autowire="byName"></bean><beanid="userServiceImpl"class="org.example.autowire.service.impl.UserServiceImpl"autowire="byName"></bean><beanid="userDao"class="org.example.autowire.dao.impl.UserDaoImpl"></bean><beanid="userDaoImpl"class="org.example.autowire.dao.impl.UserDaoImpl"></bean>

③测试

@TestpublicvoidtestAutoWireByXML(){ApplicationContext ac =newClassPathXmlApplicationContext("autowire-xml.xml");UserController userController = ac.getBean(UserController.class);
    userController.saveUser();}

3、基于注解管理Bean

从 Java 5 开始，Java 增加了对注解（Annotation）的支持，它是代码中的一种特殊标记，可以在编译、类加载和运行时被读取，执行相应的处理。开发人员可以通过注解在不改变原有代码和逻辑的情况下，在源代码中嵌入补充信息。

Spring 从 2.5 版本开始提供了对注解技术的全面支持，我们可以使用注解来实现自动装配，简化 Spring 的 XML 配置。

Spring 通过注解实现自动装配的步骤如下：

1. 引入依赖
2. 开启组件扫描
3. 使用注解定义 Bean
4. 依赖注入

3.1、搭建子模块spring6-ioc-annotation

①搭建模块

搭建方式如：spring6-ioc-xml

②引入配置文件

引入spring-ioc-xml模块日志log4j2.xml

③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></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、开启组件扫描

Spring 默认不使用注解装配 Bean，因此我们需要在 Spring 的 XML 配置中，通过

<context:component-scan>

元素开启 Spring Beans的自动扫描功能。开启此功能后，Spring 会自动从扫描指定的包（

base-package

属性设置）及其子包下的所有类，如果类上使用了

@Component

注解，就将该类装配到容器中。

<?xml version="1.0" encoding="UTF-8"?><beansxmlns="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/beans
    http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
    http://www.springframework.org/schema/context
            http://www.springframework.org/schema/context/spring-context.xsd"><!--开启组件扫描功能--><context:component-scanbase-package="org.example"></context:component-scan></beans>

注意：在使用

<context:component-scan>

元素开启自动扫描功能前，首先需要在 XML 配置的一级标签

<beans>

中添加 context 相关的约束。

情况一：最基本的扫描方式

<context:component-scanbase-package="org.example"></context:component-scan>

情况二：指定要排除的组件

<context:component-scanbase-package="org.example"><!-- context:exclude-filter标签：指定排除规则 --><!-- 
         type：设置排除或包含的依据
        type="annotation"，根据注解排除，expression中设置要排除的注解的全类名
        type="assignable"，根据类型排除，expression中设置要排除的类型的全类名
    --><context:exclude-filtertype="annotation"expression="org.springframework.stereotype.Controller"/><!--<context:exclude-filter type="assignable" expression="org.example.controller.UserController"/>--></context:component-scan>

情况三：仅扫描指定组件

<context:component-scanbase-package="org.example"use-default-filters="false"><!-- context:include-filter标签：指定在原有扫描规则的基础上追加的规则 --><!-- use-default-filters属性：取值false表示关闭默认扫描规则 --><!-- 此时必须设置use-default-filters="false"，因为默认规则即扫描指定包下所有类 --><!-- 
         type：设置排除或包含的依据
        type="annotation"，根据注解排除，expression中设置要排除的注解的全类名
        type="assignable"，根据类型排除，expression中设置要排除的类型的全类名
    --><context:include-filtertype="annotation"expression="org.springframework.stereotype.Controller"/><!--<context:include-filter type="assignable" expression="org.example.controller.UserController"/>--></context:component-scan>

3.3、使用注解定义 Bean

Spring 提供了以下多个注解，这些注解可以直接标注在 Java 类上，将它们定义成 Spring Bean。
注解说明@Component该注解用于描述 Spring 中的 Bean，它是一个泛化的概念，仅仅表示容器中的一个组件（Bean），并且可以作用在应用的任何层次，例如 Service 层、Dao 层等。 使用时只需将该注解标注在相应类上即可。@Repository该注解用于将数据访问层（Dao 层）的类标识为 Spring 中的 Bean，其功能与 @Component 相同。@Service该注解通常作用在业务层（Service 层），用于将业务层的类标识为 Spring 中的 Bean，其功能与 @Component 相同。@Controller该注解通常作用在控制层（如SpringMVC 的 Controller），用于将控制层的类标识为 Spring 中的 Bean，其功能与 @Component 相同。

3.4、实验一：@Autowired注入

单独使用

@Autowired

注解，默认根据类型装配。【默认是byType】

查看源码：

packageorg.springframework.beans.factory.annotation;importjava.lang.annotation.Documented;importjava.lang.annotation.ElementType;importjava.lang.annotation.Retention;importjava.lang.annotation.RetentionPolicy;importjava.lang.annotation.Target;@Target({ElementType.CONSTRUCTOR,ElementType.METHOD,ElementType.PARAMETER,ElementType.FIELD,ElementType.ANNOTATION_TYPE})@Retention(RetentionPolicy.RUNTIME)@Documentedpublic@interfaceAutowired{booleanrequired()defaulttrue;}

源码中有两处需要注意：

• 第一处：该注解可以标注在哪里？
• • 构造方法上- 方法上- 形参上- 属性上- 注解上
• 第二处：该注解有一个required属性，默认值是true，表示在注入的时候要求被注入的Bean必须是存在的，如果不存在则报错。如果required属性设置为false，表示注入的Bean存在或者不存在都没关系，存在的话就注入，不存在的话，也不报错。

①场景一：属性注入

创建UserDao接口

packageorg.example.dao;publicinterfaceUserDao{publicvoidprint();}

创建UserDaoImpl实现

packageorg.example.dao.impl;importorg.example.dao.UserDao;importorg.springframework.stereotype.Repository;@RepositorypublicclassUserDaoImplimplementsUserDao{@Overridepublicvoidprint(){System.out.println("Dao层执行结束");}}

创建UserService接口

packageorg.example.spring6.service;publicinterfaceUserService{publicvoidout();}

创建UserServiceImpl实现类

packageorg.example.spring6.service.impl;importorg.example.spring6.dao.UserDao;importorg.example.spring6.service.UserService;importorg.springframework.beans.factory.annotation.Autowired;importorg.springframework.stereotype.Service;@ServicepublicclassUserServiceImplimplementsUserService{@AutowiredprivateUserDao userDao;@Overridepublicvoidout(){
        userDao.print();System.out.println("Service层执行结束");}}

创建UserController类

packageorg.exampleu.spring6.controller;importorg.example.spring6.service.UserService;importorg.springframework.beans.factory.annotation.Autowired;importorg.springframework.stereotype.Controller;@ControllerpublicclassUserController{@AutowiredprivateUserService userService;publicvoidout(){
        userService.out();System.out.println("Controller层执行结束。");}}

测试一

packageorg.example.spring6.bean;importorg.example.spring6.controller.UserController;importorg.junit.jupiter.api.Test;importorg.slf4j.Logger;importorg.slf4j.LoggerFactory;importorg.springframework.context.ApplicationContext;importorg.springframework.context.support.ClassPathXmlApplicationContext;publicclassUserTest{privateLogger logger =LoggerFactory.getLogger(UserTest.class);@TestpublicvoidtestAnnotation(){ApplicationContext context =newClassPathXmlApplicationContext("Beans.xml");UserController userController = context.getBean("userController",UserController.class);
        userController.out();
        logger.info("执行成功");}}

以上构造方法和setter方法都没有提供，经过测试，仍然可以注入成功。

②场景二：set注入

修改UserServiceImpl类

packageorg.example.service.impl;importorg.example.dao.UserDao;importorg.example.service.UserService;importorg.springframework.beans.factory.annotation.Autowired;importorg.springframework.stereotype.Service;@ServicepublicclassUserServiceImplimplementsUserService{privateUserDao userDao;@AutowiredpublicvoidsetUserDao(UserDao userDao){this.userDao = userDao;}@Overridepublicvoidout(){
        userDao.print();System.out.println("Service层执行结束");}}

修改UserController类

packageorg.example.controller;importorg.example.service.UserService;importorg.springframework.beans.factory.annotation.Autowired;importorg.springframework.stereotype.Controller;@ControllerpublicclassUserController{privateUserService userService;@AutowiredpublicvoidsetUserService(UserService userService){this.userService = userService;}publicvoidout(){
        userService.out();System.out.println("Controller层执行结束。");}}

测试：成功调用

③场景三：构造方法注入

修改UserServiceImpl类

packageorg.example.service.impl;importorg.example.dao.UserDao;importorg.example.service.UserService;importorg.springframework.beans.factory.annotation.Autowired;importorg.springframework.stereotype.Service;@ServicepublicclassUserServiceImplimplementsUserService{privateUserDao userDao;@AutowiredpublicUserServiceImpl(UserDao userDao){this.userDao = userDao;}@Overridepublicvoidout(){
        userDao.print();System.out.println("Service层执行结束");}}

修改UserController类

packageorg.example.controller;importorg.example.service.UserService;importorg.springframework.beans.factory.annotation.Autowired;importorg.springframework.stereotype.Controller;@ControllerpublicclassUserController{privateUserService userService;@AutowiredpublicUserController(UserService userService){this.userService = userService;}publicvoidout(){
        userService.out();System.out.println("Controller层执行结束。");}}

测试：成功调用

注：在 Spring4.x 中增加了新的特性：如果类只提供了一个带参数的构造方法，则不需要对对其内部的属性写 @Autowired 注解，Spring 会自动为你注入属性。（请看场景五）

④场景四：形参上注入

修改UserServiceImpl类

packageorg.example.service.impl;importorg.example.spring6.dao.UserDao;importorg.example.service.UserService;importorg.springframework.beans.factory.annotation.Autowired;importorg.springframework.stereotype.Service;@ServicepublicclassUserServiceImplimplementsUserService{privateUserDao userDao;publicUserServiceImpl(@AutowiredUserDao userDao){this.userDao = userDao;}@Overridepublicvoidout(){
        userDao.print();System.out.println("Service层执行结束");}}

修改UserController类

packageorg.example.controller;importorg.example.service.UserService;importorg.springframework.beans.factory.annotation.Autowired;importorg.springframework.stereotype.Controller;@ControllerpublicclassUserController{privateUserService userService;publicUserController(@AutowiredUserService userService){this.userService = userService;}publicvoidout(){
        userService.out();System.out.println("Controller层执行结束。");}}

测试：成功调用

⑤场景五：只有一个构造函数，无注解

修改UserServiceImpl类

packageorg.example.service.impl;importorg.example.dao.UserDao;importorg.example.service.UserService;importorg.springframework.beans.factory.annotation.Autowired;importorg.springframework.beans.factory.annotation.Qualifier;importorg.springframework.stereotype.Service;@ServicepublicclassUserServiceImplimplementsUserService{@AutowiredprivateUserDao userDao;publicUserServiceImpl(UserDao userDao){this.userDao = userDao;}@Overridepublicvoidout(){
        userDao.print();System.out.println("Service层执行结束");}}

测试通过

当有参数的构造方法只有一个时，@Autowired注解可以省略。

说明：有多个构造方法时呢？大家可以测试（再添加一个无参构造函数），测试报错

⑥场景六：@Autowired注解和@Qualifier注解联合

添加dao层实现

packageorg.example.dao.impl;importorg.example.dao.UserDao;importorg.springframework.stereotype.Repository;@RepositorypublicclassUserDaoRedisImplimplementsUserDao{@Overridepublicvoidprint(){System.out.println("Redis Dao层执行结束");}}

测试：测试异常

错误信息中说：不能装配，UserDao这个Bean的数量等于2

怎么解决这个问题呢？当然要byName，根据名称进行装配了。

修改UserServiceImpl类

packageorg.example.service.impl;importorg.example.dao.UserDao;importorg.example.service.UserService;importorg.springframework.beans.factory.annotation.Autowired;importorg.springframework.stereotype.Service;@ServicepublicclassUserServiceImplimplementsUserService{@Autowired@Qualifier("userDaoImpl")// 指定bean的名字privateUserDao userDao;@Overridepublicvoidout(){
        userDao.print();System.out.println("Service层执行结束");}}

总结

• @Autowired注解可以出现在：属性上、构造方法上、构造方法的参数上、setter方法上。
• 当带参数的构造方法只有一个，@Autowired注解可以省略。（）
• @Autowired注解默认根据类型注入。如果要根据名称注入的话，需要配合@Qualifier注解一起使用。

3.5、实验二：@Resource注入

@Resource

注解也可以完成属性注入。那它和@Autowired注解有什么区别？

• @Resource注解是JDK扩展包中的，也就是说属于JDK的一部分。所以该注解是标准注解，更加具有通用性。(JSR-250标准中制定的注解类型。JSR是Java规范提案。)
• @Autowired注解是Spring框架自己的。
• @Resource注解默认根据名称装配byName，未指定name时，使用属性名作为name。通过name找不到的话会自动启动通过类型byType装配。
• @Autowired注解默认根据类型装配byType，如果想根据名称装配，需要配合@Qualifier注解一起用。
• @Resource注解用在属性上、setter方法上。
• @Autowired注解用在属性上、setter方法上、构造方法上、构造方法参数上。

@Resource注解属于JDK扩展包，所以不在JDK当中，需要额外引入以下依赖：【如果是JDK8的话不需要额外引入依赖。高于JDK11或低于JDK8需要引入以下依赖。】

<dependency><groupId>jakarta.annotation</groupId><artifactId>jakarta.annotation-api</artifactId><version>2.1.1</version></dependency>

源码：

packagejakarta.annotation;importjava.lang.annotation.ElementType;importjava.lang.annotation.Repeatable;importjava.lang.annotation.Retention;importjava.lang.annotation.RetentionPolicy;importjava.lang.annotation.Target;@Target({ElementType.TYPE,ElementType.FIELD,ElementType.METHOD})@Retention(RetentionPolicy.RUNTIME)@Repeatable(Resources.class)public@interfaceResource{Stringname()default"";Stringlookup()default"";Class<?>type()defaultObject.class;Resource.AuthenticationTypeauthenticationType()defaultResource.AuthenticationType.CONTAINER;booleanshareable()defaulttrue;StringmappedName()default"";Stringdescription()default"";publicstaticenumAuthenticationType{
        CONTAINER,
        APPLICATION;privateAuthenticationType(){}}}

①场景一：根据name注入

修改UserDaoImpl类

packageorg.example.dao.impl;importorg.example.dao.UserDao;importorg.springframework.stereotype.Repository;@Repository("myUserDao")publicclassUserDaoImplimplementsUserDao{@Overridepublicvoidprint(){System.out.println("Dao层执行结束");}}

修改UserServiceImpl类

packageorg.example.service.impl;importorg.example.dao.UserDao;importorg.example.service.UserService;importjakarta.annotation.Resource;importorg.springframework.beans.factory.annotation.Autowired;importorg.springframework.beans.factory.annotation.Qualifier;importorg.springframework.stereotype.Service;@ServicepublicclassUserServiceImplimplementsUserService{@Resource(name ="myUserDao")privateUserDao myUserDao;@Overridepublicvoidout(){
        myUserDao.print();System.out.println("Service层执行结束");}}

测试通过

②场景二：name未知注入

修改UserDaoImpl类

packageorg.example.dao.impl;importorg.example.dao.UserDao;importorg.springframework.stereotype.Repository;@Repository("myUserDao")publicclassUserDaoImplimplementsUserDao{@Overridepublicvoidprint(){System.out.println("Dao层执行结束");}}

修改UserServiceImpl类

packageorg.example.service.impl;importorg.example.dao.UserDao;importorg.example.service.UserService;importjakarta.annotation.Resource;importorg.springframework.beans.factory.annotation.Autowired;importorg.springframework.beans.factory.annotation.Qualifier;importorg.springframework.stereotype.Service;@ServicepublicclassUserServiceImplimplementsUserService{@ResourceprivateUserDao myUserDao;@Overridepublicvoidout(){
        myUserDao.print();System.out.println("Service层执行结束");}}

测试通过

当

@Resource

注解使用时没有指定name的时候，还是根据name进行查找，这个name是 属性名 。

③场景三 其他情况

修改UserServiceImpl类，userDao1属性名不存在

packageorg.example.service.impl;importorg.example.dao.UserDao;importorg.example.service.UserService;importjakarta.annotation.Resource;importorg.springframework.beans.factory.annotation.Autowired;importorg.springframework.beans.factory.annotation.Qualifier;importorg.springframework.stereotype.Service;@ServicepublicclassUserServiceImplimplementsUserService{@ResourceprivateUserDao userDao1;@Overridepublicvoidout(){
        userDao1.print();System.out.println("Service层执行结束");}}

测试异常

根据异常信息得知：显然当通过name找不到的时候，自然会启动byType进行注入，以上的错误是因为UserDao接口下有两个实现类导致的。所以根据类型注入就会报错。

@Resource的set注入可以自行测试

总结：

@Resource注解：默认byName注入，没有指定name时把属性名当做name，根据name找不到时，才会byType注入。byType注入时，某种类型的Bean只能有一个

3.6、Spring全注解开发

全注解开发就是不再使用spring配置文件了，写一个配置类来代替配置文件。

packageorg.example.config;importorg.springframework.context.annotation.ComponentScan;importorg.springframework.context.annotation.Configuration;@Configuration//@ComponentScan({"org.example.controller", "org.example.service","org.example.dao"})@ComponentScan("org.example")publicclassSpring6Config{}

测试类

@TestpublicvoidtestAllAnnotation(){ApplicationContext context =newAnnotationConfigApplicationContext(Spring6Config.class);UserController userController = context.getBean("userController",UserController.class);
    userController.out();
    logger.info("执行成功");}