Spring IoC 依赖注入(支持哪些数据类型？)

左手的ㄟ右手 2022-10-30 01:26 120阅读 0赞

Dependency Injection，依赖注入。

*  对象之间依赖关系的管理交给 Spring 维护；
 *  是实现控制反转的方式之一；
 *  可以降低程序之间的耦合(依赖关系)。

Spring 实现的 IoC 容器中，基本类型和对象都可以注入，按配置细节区分：

*  Java 基本类型
 *  String
 *  bean
 *  Spring 自建 bean(未自己申明的 bean，可以通过 getBean 方法获取到)
 *  非 bean(无法通过 getBean 方法获取到)
 *  数组
 *  集合(List、Set、Map)

使用 setter 方法演示以上数据类型的注入

bean 的类

package constxiong.datatype;
    
    import java.util.Arrays;
    import java.util.List;
    import java.util.Map;
    import java.util.Set;
    
    public class User {
    
        private double id;
    
        private String name;
    
        private User wife;
    
        private User[] friends;
    
        private List<User> schoolmates;
    
        private Set<String> favorites;
    
        private Map<String, String> emails;
    
        public void setId(double id) {
            this.id = id;
        }
    
        public void setName(String name) {
            this.name = name;
        }
    
        public void setWife(User wife) {
            this.wife = wife;
        }
    
        public void setFriends(User[] friends) {
            this.friends = friends;
        }
    
        public void setSchoolmates(List<User> schoolmates) {
            this.schoolmates = schoolmates;
        }
    
        public void setFavorites(Set<String> favorites) {
            this.favorites = favorites;
        }
    
        public void setEmails(Map<String, String> emails) {
            this.emails = emails;
        }
    
        @Override
        public String toString() {
            return "User [id=" + id + ", name=" + name + ", wife=" + wife + ", friends=" + Arrays.toString(friends)
                    + ", schoolmates=" + schoolmates + ", favorites=" + favorites + ", emails=" + emails + "]";
        }
    
    }

xml 配置文件

<?xml version="1.0" encoding="UTF-8"?>
    <beans xmlns="http://www.springframework.org/schema/beans"
           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
           xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
    
        <bean id="wife" class="constxiong.datatype.User">
            <property name="id" value="2"/>
            <property name="name" value="wife"/>
        </bean>
    
        <bean id="ConstXiong" class="constxiong.datatype.User">
            <property name="id" value="1"/>
            <property name="name" value="ConstXiong"/>
            <property name="wife" ref="wife"/>
            <property name="friends">
                <list>
                    <ref bean="wife"/>
                </list>
            </property>
            <property name="schoolmates">
                <list>
                    <ref bean="wife"/>
                </list>
            </property>
            <property name="favorites">
                <set>
                    <value>写代码</value>
                    <value>睡觉</value>
                </set>
            </property>
            <property name="emails">
                <map>
                    <entry key="公司" value="123@123.com"></entry>
                    <entry key="个人" value="123@abc.com"></entry>
                </map>
            </property>
        </bean>
    
    </beans>

测试代码

package constxiong.datatype;
    
    import org.springframework.beans.factory.BeanFactory;
    import org.springframework.context.support.ClassPathXmlApplicationContext;
    
    /**
     * 依赖注入-可注入的数据类型
     */
    public class Test {
    
        @SuppressWarnings("resource")
        public static void main(String[] args) {
            BeanFactory factory = new ClassPathXmlApplicationContext("META-INF/spring-dependency-injection-datatype.xml");
            User constxiong = (User)factory.getBean("ConstXiong");
            System.out.println(constxiong);
        }
    
    }

结果打印

User [id=1.0, name=ConstXiong, wife=User [id=2.0, name=wife, wife=null, friends=null, schoolmates=null, favorites=null, emails=null], friends=[User [id=2.0, name=wife, wife=null, friends=null, schoolmates=null, favorites=null, emails=null]], schoolmates=[User [id=2.0, name=wife, wife=null, friends=null, schoolmates=null, favorites=null, emails=null]], favorites=[写代码, 睡觉], emails={公司=123@123.com, 个人=123@abc.com}]

上面这个例子演示了基本类型 double、String、bean、数组、List、Set、Map 的注入，不难看懂，不多解释。

那什么是 Spring 自建的 bean 和 非 bean 呢？这两个概念，看下面这个例子。

新增类 SpecialUser，包含了 BeanFactory 和 Environment 两个类型的属性

package constxiong.datatype;
    
    import org.springframework.beans.factory.BeanFactory;
    import org.springframework.core.env.Environment;
    
    public class SpecialUser {
    
        private BeanFactory beanFactory;
    
        private Environment environment;
    
        public BeanFactory getBeanFactory() {
            return beanFactory;
        }
    
        public void setBeanFactory(BeanFactory beanFactory) {
            this.beanFactory = beanFactory;
        }
    
        public Environment getEnvironment() {
            return environment;
        }
    
        public void setEnvironment(Environment environment) {
            this.environment = environment;
        }
    
    }

xml 新增一个 bean 配置

<bean id="specialUser" class="constxiong.datatype.SpecialUser" autowire="byType">
    </bean>

测试类的 main 方法中新增测试代码

SpecialUser specialUser = (SpecialUser)factory.getBean("specialUser");
    //Spring 自建 bean，并未在 spring-dependency-injection-datatype.xml 配置文件中申明，却可以注入与依赖查找
    System.out.println(specialUser.getEnvironment());//通过 autowire="byType" 可以注入成功
    System.out.println(factory.getBean(Environment.class));
    
    //非 bean，可以注入，但无法通过 getBean 方法依赖查找
    System.out.println(specialUser.getBeanFactory());//通过 autowire="byType" 可以注入成功
    System.out.println(factory.getBean(BeanFactory.class));//getBean 方法无法获取到 BeanFactory

打印结果

StandardEnvironment {activeProfiles=[], defaultProfiles=[default], propertySources=[PropertiesPropertySource {name='systemProperties'}, SystemEnvironmentPropertySource {name='systemEnvironment'}]}
    StandardEnvironment {activeProfiles=[], defaultProfiles=[default], propertySources=[PropertiesPropertySource {name='systemProperties'}, SystemEnvironmentPropertySource {name='systemEnvironment'}]}
    org.springframework.beans.factory.support.DefaultListableBeanFactory@3498ed: defining beans [wife,ConstXiong,specialUser]; root of factory hierarchy
    Exception in thread "main" org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'org.springframework.beans.factory.BeanFactory' available
        at org.springframework.beans.factory.support.DefaultListableBeanFactory.getBean(DefaultListableBeanFactory.java:351)
        at org.springframework.beans.factory.support.DefaultListableBeanFactory.getBean(DefaultListableBeanFactory.java:342)
        at org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:1126)
        at constxiong.datatype.Test.main(Test.java:26)

从打印结果可以看出

*  Environment bean 并未在 xml 中配置，但却可以注入与通过 getBean 方法依赖查找，即上面提到的 Spring 自建的 bean
 *  BeanFactory 可以被注入，但通过 getBean 方法获取报找不到 bean 的错误，即上面提到的非 bean

ps：

文末引出的自建 bean 与非 bean 还包含哪些类？依赖注入又有哪些实现方式？

限于篇幅，后续研究。

--------------------

### 【Java学习资源】整理推荐 ###

*  [Spring 依赖注入的处理过程与 DependencyDescriptor 的说明][Spring _ DependencyDescriptor]
 *  [Spring 各种 Aware 接口回调注入][Spring _ Aware]
 *  [Spring Bean 生命周期内的 Exception 复现][Spring Bean _ Exception]
 *  [Spring 内建 Bean][Spring _ Bean]
 *  [Spring Bean 的别名][Spring Bean]
 *  [Spring Bean 未指定名称的命名规则][Spring Bean 1]
 *  [Bean 何时被 GC][Bean _ GC]
 *  [Spring Bean 延迟加载][Spring Bean 2]
 *  [ObjectFactory 与 BeanFactory 的区别][ObjectFactory _ BeanFactory]
 *  [Bean 销毁的方式与顺序][Bean]
 *  [Bean 初始化的方式与顺序][Bean 1]
 *  [Bean 的实例化方式][Bean 2]
 *  [Bean的注册方式][Bean 3]
 *  [什么是 BeanDefinition？][BeanDefinition]
 *  [Spring IoC 容器启动时做了什么？][Spring IoC]
 *  [BeanFactory 与 FactoryBean 的区别][BeanFactory _ FactoryBean]
 *  [BeanFactory 与 ApplicationContext 的区别][BeanFactory _ ApplicationContext]
 *  [Spring IoC 依赖注入的实现方式][Spring IoC 1]
 *  [Spring IoC 依赖注入(支持哪些数据类型？)][Spring IoC 2]
 *  [Spring bean 依赖查找][Spring bean]
 *  [Spring-IoC][]
 *  [Spring 的核心特性][Spring]

--------------------

### 【Java面试题与答案】整理推荐 ###

*  [基础与语法][Link 1]
 *  [集合][Link 2]
 *  [网络编程][Link 3]
 *  [并发编程][Link 4]
 *  [Web][]
 *  [安全][Link 5]
 *  [设计模式][Link 6]
 *  [框架][Link 7]
 *  [算法与数据结构][Link 8]
 *  [异常][Link 9]
 *  [文件解析与生成][Link 10]
 *  [Linux][]
 *  [MySQL][]
 *  [Oracle][]
 *  [Redis][]
 *  [Dubbo][]

[Spring _ DependencyDescriptor]: https://www.javanav.com/val/152161d266a94fd38efb365a78d8f9a3.html
[Spring _ Aware]: https://www.javanav.com/val/089b3993c8bc4dec891ea677c104c5e4.html
[Spring Bean _ Exception]: https://www.javanav.com/val/2b31b7061b3342c0a67f8d7fc7373ed3.html
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[BeanDefinition]: https://www.javanav.com/val/e82279480ec24184bcaf723a50ef08b3.html
[Spring IoC]: https://www.javanav.com/val/d382c8380fc2480788a35a7e671b5e9b.html
[BeanFactory _ FactoryBean]: https://www.javanav.com/val/173e873a2c98499a8a08a13b4f88ae10.html
[BeanFactory _ ApplicationContext]: https://www.javanav.com/val/bbc2c9580b7045e583855925d5f1a50b.html
[Spring IoC 1]: https://www.javanav.com/val/a835e6c709ea439ebb21a80f1bf77926.html
[Spring IoC 2]: https://www.javanav.com/val/e377beac22644c2c85308079b239a0fd.html
[Spring bean]: https://www.javanav.com/val/7f8c2e1f24db46e79bc4b9b04f9ad715.html
[Spring-IoC]: https://www.javanav.com/val/a412668efda74412a13f6df9a6d2c714.html
[Spring]: https://www.javanav.com/val/6eac12a548ea40c68ff64b1af307563a.html
[Link 1]: https://www.javanav.com/interview/93b0069472fd479393006c0e73043fc4.html
[Link 2]: https://www.javanav.com/interview/4147d95e693945e7a50345fd33ec817e.html
[Link 3]: https://www.javanav.com/interview/68a57ffc78de4133bb890bdd502ac418.html
[Link 4]: https://www.javanav.com/interview/36a24fa3258e45c89873f474ce914912.html
[Web]: https://www.javanav.com/interview/4e27cb63adb440c6825a159d35cf4010.html
[Link 5]: https://www.javanav.com/interview/03affb2ce3f04fda8853f714e5764906.html
[Link 6]: https://www.javanav.com/interview/07a32a9ff17a4006a53550ce658cafed.html
[Link 7]: https://www.javanav.com/interview/5c466456e9b54ab0a749b5948e51f1d3.html
[Link 8]: https://www.javanav.com/interview/943f917041ee4f05add24539f5b861b2.html
[Link 9]: https://www.javanav.com/interview/d3f058cfc05d4c6dadd821b622e84d36.html
[Link 10]: https://www.javanav.com/interview/67a50996c28f418e83b109ea42fc3eff.html
[Linux]: https://www.javanav.com/interview/00cccb81729540d1923bd0a0ef49533a.html
[MySQL]: https://www.javanav.com/interview/d311e78502a845f1a4bb307bd6aec2b3.html
[Oracle]: https://www.javanav.com/interview/5f29e9677edf4a16be3dce30d257c9ab.html
[Redis]: https://www.javanav.com/interview/066c62b3af4d4827b2243a822c3084a9.html
[Dubbo]: https://www.javanav.com/interview/9a3e7a7740324757abaab953f7ebc455.html