Spring核心编程思想(十四)Spring IoC 容器概述之Spring IoC 依赖查找

小马哥课程笔记

依赖查找

• 根据 Bean 名称查找
  • 实时查找
  • 延迟查找
• 根据 Bean 类型查找
  • 单个 Bean 对象
  • 集合 Bean 对象
• 根据 Bean 名称 + 类型查找
• 根据 Java 注解查找
  • 单个 Bean 对象
  • 集合 Bean 对象

代码示例

依赖查找

/**
 * 依赖查找示例
 * 1. 通过名称的方式来查找
 * 2. 通过类型的方式来查找
 * 3. 通过注解的方式来查找
 *
 * @author <a href="mailto:mercyblitz@gmail.com">Mercy</a>
 * @since
 */
public class DependencyLookupDemo {

    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-lookup-context.xml");
        // 按照类型查找
        lookupByType(beanFactory);
        // 按照类型查找集合对象
        lookupCollectionByType(beanFactory);
        // 通过注解查找对象
        lookupByAnnotationType(beanFactory);

//        lookupInRealTime(beanFactory);
//        lookupInLazy(beanFactory);
    }

    private static void lookupByAnnotationType(BeanFactory beanFactory) {
        if (beanFactory instanceof ListableBeanFactory) {
            ListableBeanFactory listableBeanFactory = (ListableBeanFactory) beanFactory;
            Map<String, User> users = (Map) listableBeanFactory.getBeansWithAnnotation(Super.class);
            System.out.println("查找标注 @Super 所有的 User 集合对象：" + users);
        }
    }

    private static void lookupCollectionByType(BeanFactory beanFactory) {
        if (beanFactory instanceof ListableBeanFactory) {
            ListableBeanFactory listableBeanFactory = (ListableBeanFactory) beanFactory;
            Map<String, User> users = listableBeanFactory.getBeansOfType(User.class);
            System.out.println("查找到的所有的 User 集合对象：" + users);
        }
    }

    private static void lookupByType(BeanFactory beanFactory) {
        User user = beanFactory.getBean(User.class);
        System.out.println("实时查找：" + user);
    }

    private static void lookupInLazy(BeanFactory beanFactory) {
        ObjectFactory<User> objectFactory = (ObjectFactory<User>) beanFactory.getBean("objectFactory");
        User user = objectFactory.getObject();
        System.out.println("延迟查找：" + user);
    }

    private static void lookupInRealTime(BeanFactory beanFactory) {
        User user = (User) beanFactory.getBean("user");
        System.out.println("实时查找：" + user);
    }
}

annotation

/**
 * 超级
 *
 * @author <a href="mailto:mercyblitz@gmail.com">Mercy</a>
 * @since
 */
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
public @interface Super {
}

bean

/**
 * 用户类
 *
 * @author <a href="mailto:mercyblitz@gmail.com">Mercy</a>
 * @since
 */
public class User implements BeanNameAware {

    private Long id;

    private String name;
}


/**
 * 超级用户
 *
 * @author <a href="mailto:mercyblitz@gmail.com">Mercy</a>
 * @since
 */
@Super
public class SuperUser extends User {

    private String address;

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    @Override
    public String toString() {
        return "SuperUser{" +
                "address='" + address + '\'' +
                "} " + super.toString();
    }
}

xml-bean-context (上下文的实例)

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

<!--    <context:annotation-config/>-->

<!--    <context:component-scan base-package="org.acme" />-->

    <!-- Root BeanDefinition 不需要合并，不存在 parent -->
    <!-- 普通 beanDefinition GenericBeanDefinition -->
    <!-- 经过合并后 GenericBeanDefinition 变成 RootBeanDefinition -->
    <bean id="user" class="org.geekbang.thinking.in.spring.ioc.overview.domain.User">
        <property name="id" value="1"/>
        <property name="name" value="小马哥"/>
        <property name="city" value="HANGZHOU"/>
        <property name="workCities" value="BEIJING,HANGZHOU"/>
        <property name="lifeCities">
            <list>
                <value>BEIJING</value>
                <value>SHANGHAI</value>
            </list>
        </property>
        <property name="configFileLocation" value="classpath:/META-INF/user-config.properties"/>
    </bean>

    <!-- 普通 beanDefinition GenericBeanDefinition -->
    <!-- 合并后 GenericBeanDefinition 变成 RootBeanDefinition，并且覆盖 parent 相关配置-->
    <!-- primary = true , 增加了一个 address 属性 -->
    <bean id="superUser" class="org.geekbang.thinking.in.spring.ioc.overview.domain.SuperUser" parent="user"
          primary="true">
        <property name="address" value="杭州"/>
    </bean>

    <bean id="objectFactory" class="org.springframework.beans.factory.config.ObjectFactoryCreatingFactoryBean">
        <property name="targetBeanName" value="user"/>
    </bean>

</beans>