Spring核心编程思想(十五)Spring IoC 容器概述之Spring IoC 依赖注入

小马哥课程笔记

• 根据 Bean 名称注入
• 根据 Bean 类型注入
  • 单个 Bean 对象
  • 集合 Bean 对象
• 注入容器內建 Bean 对象
• 注入非 Bean 对象
• 注入类型
  • 实时注入
  • 延迟注入

代码示例

依赖注入

/**
 * 依赖注入示例
 * 可以发现BeanFactory不是一个普通的Bean 通过依赖注入可以获得但是又不和通过上下文获取的beanFactory相等  通过依赖查找无法获得
 * 此处的beanFactory和applicationContext相等
 *
 * @author <a href="mailto:mercyblitz@gmail.com">Mercy</a>
 * @since
 */
public class DependencyInjectionDemo {

    public static void main(String[] args) {
        // 配置 XML 配置文件
        // 启动 Spring 应用上下文
//        BeanFactory beanFactory = new ClassPathXmlApplicationContext("classpath:/META-INF/dependency-injection-context.xml");

        ApplicationContext applicationContext = new ClassPathXmlApplicationContext("classpath:/META-INF/dependency-injection-context.xml");

        // 依赖来源一：自定义 Bean
        UserRepository userRepository = applicationContext.getBean("userRepository", UserRepository.class);

//        System.out.println(userRepository.getUsers());

        // 依赖来源二：依赖注入（內建依赖）
        System.out.println(userRepository.getBeanFactory());

        //延时注入
        ObjectFactory userFactory = userRepository.getObjectFactory();

        System.out.println(userFactory.getObject() == applicationContext);

        // 依赖查找（错误）
//        System.out.println(beanFactory.getBean(BeanFactory.class));

        // 依赖来源三：容器內建 Bean
        Environment environment = applicationContext.getBean(Environment.class);
        System.out.println("获取 Environment 类型的 Bean：" + environment);
    }

    private static void whoIsIoCContainer(UserRepository userRepository, ApplicationContext applicationContext) {


        // ConfigurableApplicationContext <- ApplicationContext <- BeanFactory

        // ConfigurableApplicationContext#getBeanFactory()


        // 这个表达式为什么不会成立
        System.out.println(userRepository.getBeanFactory() == applicationContext);

        // ApplicationContext is BeanFactory

    }

}

context 上下文

• autowire=“byType” 根据类型注入

<?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/beans https://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/util https://www.springframework.org/schema/util/spring-util.xsd">

    <!-- 通过导入复用 dependency-lookup-context.xml -->
    <import resource="dependency-lookup-context.xml"/>

    <bean id="userRepository" class="org.geekbang.thinking.in.spring.ioc.overview.repository.UserRepository"
          autowire="byType"> <!-- Auto-Wiring -->
        <!-- 手动配置 -->
        <!--        <property name="users">-->
        <!--            <util:list>-->
        <!--                <ref bean="superUser" />-->
        <!--                <ref bean="user" />-->
        <!--            </util:list>-->
        <!--        </property>-->

    </bean>
</beans>

set注入的repository

/**
 * 用户信息仓库
 *
 * @author <a href="mailto:mercyblitz@gmail.com">Mercy</a>
 * @since
 */
public class UserRepository {

    private Collection<User> users; // 自定义 Bean

    private BeanFactory beanFactory; // 內建非 Bean 对象（依赖）

    private ObjectFactory<ApplicationContext> objectFactory;

    public Collection<User> getUsers() {
        return users;
    }

    public void setUsers(Collection<User> users) {
        this.users = users;
    }


    public void setBeanFactory(BeanFactory beanFactory) {
        this.beanFactory = beanFactory;
    }

    public BeanFactory getBeanFactory() {
        return beanFactory;
    }

    public ObjectFactory<ApplicationContext> getObjectFactory() {
        return objectFactory;
    }

    public void setObjectFactory(ObjectFactory<ApplicationContext> objectFactory) {
        this.objectFactory = objectFactory;
    }
}