懒加载Spring bean

如果一个bean是延迟加载的，那么延迟加载的bean中定义的所有bean都会被延迟加载吗？ （即使它们没有定义@Lazy）

这是测试项目：https://github.com/madhur/conditional-property-test/blob/master/src/main/java/com/example/demo/EventPublishService.java https://github.com/madhur/conditional-property-test/blob/master/src/main/java/com/example/demo/EventPublishService.java

我有这些豆子：

@Service
@ConditionalOnProperty(
        name = {"publish.feed.events"},
        havingValue = "true"
)
public class EventPublishService {
 
     @Autowired
     private KafkaPublisher kafkaPublisher;

}

////////////////////////////////////////

@Service
public class EventService {

    @Autowired
    @Lazy
    private EventPublishService eventPublishService;

    @Value("${publish.feed.events:false}")
    private boolean isPublishEvents;
}

//////////////////////////////////////////////////

@Component
public class KafkaPublisher {

    @Value("${kafka.producer.financial_feed.topic}")
    private String financeFeedTopic;
}

我的任何 application.properties 只有一个属性，

publish.feed.events=false

因为，我没有加载EventPublishServicebeans（因为属性为 false），我期望依赖 beanKafkaPublisher也不应该被加载。但是，我在启动时收到错误，这意味着KafkaPublisherbean 正在加载，尽管EventPublishServicebean 没有被加载。

我怎样才能确保KafkaPublisherbean 不应该被加载吗？ 因此，对于任何不需要财产的人来说，财产不应该是强制性的EventPublishService bean?

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'kafkaPublisher': Injection of autowired dependencies failed; nested exception is java.lang.IllegalArgumentException: Could not resolve placeholder 'kafka.producer.financial_feed.topic' in value "${kafka.producer.financial_feed.topic}"
        at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:379) ~[spring-beans-5.0.5.RELEASE.jar:5.0.5.RELEASE]
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1344) ~[spring-beans-5.0.5.RELEASE.jar:5.0.5.RELEASE]
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:578) ~[spring-beans-5.0.5.RELEASE.jar:5.0.5.RELEASE]
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:501) ~[spring-beans-5.0.5.RELEASE.jar:5.0.5.RELEASE]
        at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:317) ~[spring-beans-5.0.5.RELEASE.jar:5.0.5.RELEASE]
        at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:228) ~[spring-beans-5.0.5.RELEASE.jar:5.0.5.RELEASE]
        at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:315) ~[spring-beans-5.0.5.RELEASE.jar:5.0.5.RELEASE]
        at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199) ~[spring-beans-5.0.5.RELEASE.jar:5.0.5.RELEASE]
        at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:760) ~[spring-beans-5.0.5.RELEASE.jar:5.0.5.RELEASE]
        at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:869) ~[spring-context-5.0.5.RELEASE.jar:5.0.5.RELEASE]
        at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:550) ~[spring-context-5.0.5.RELEASE.jar:5.0.5.RELEASE]
        at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:759) [spring-boot-2.0.1.RELEASE.jar:2.0.1.RELEASE]
        at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:395) [spring-boot-2.0.1.RELEASE.jar:2.0.1.RELEASE]
        at org.springframework.boot.SpringApplication.run(SpringApplication.java:327) [spring-boot-2.0.1.RELEASE.jar:2.0.1.RELEASE]
        at org.springframework.boot.SpringApplication.run(SpringApplication.java:1255) [spring-boot-2.0.1.RELEASE.jar:2.0.1.RELEASE]
        at org.springframework.boot.SpringApplication.run(SpringApplication.java:1243) [spring-boot-2.0.1.RELEASE.jar:2.0.1.RELEASE]
        at com.example.demo.DemoApplication.main(DemoApplication.java:17) [main/:na] Caused by: java.lang.IllegalArgumentException: Could not resolve placeholder 'kafka.producer.financial_feed.topic' in value "${kafka.producer.financial_feed.topic}"
        at org.springframework.util.PropertyPlaceholderHelper.parseStringValue(PropertyPlaceholderHelper.java:172) ~[spring-core-5.0.5.RELEASE.jar:5.0.5.RELEASE]
        at org.springframework.util.PropertyPlaceholderHelper.replacePlaceholders(PropertyPlaceholderHelper.java:124) ~[spring-core-5.0.5.RELEASE.jar:5.0.5.RELEASE]
        at org.springframework.core.env.AbstractPropertyResolver.doResolvePlaceholders(AbstractPropertyResolver.java:237) ~[spring-core-5.0.5.RELEASE.jar:5.0.5.RELEASE]
        at org.springframework.core.env.AbstractPropertyResolver.resolveRequiredPlaceholders(AbstractPropertyResolver.java:211) ~[spring-core-5.0.5.RELEASE.jar:5.0.5.RELEASE]
        at org.springframework.context.support.PropertySourcesPlaceholderConfigurer.lambda$processProperties$0(PropertySourcesPlaceholderConfigurer.java:175) ~[spring-context-5.0.5.RELEASE.jar:5.0.5.RELEASE]
        at org.springframework.beans.factory.support.AbstractBeanFactory.resolveEmbeddedValue(AbstractBeanFactory.java:839) ~[spring-beans-5.0.5.RELEASE.jar:5.0.5.RELEASE]
        at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1086) ~[spring-beans-5.0.5.RELEASE.jar:5.0.5.RELEASE]
        at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1065) ~[spring-beans-5.0.5.RELEASE.jar:5.0.5.RELEASE]
        at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:584) ~[spring-beans-5.0.5.RELEASE.jar:5.0.5.RELEASE]
        at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:91) ~[spring-beans-5.0.5.RELEASE.jar:5.0.5.RELEASE]
        at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:373) ~[spring-beans-5.0.5.RELEASE.jar:5.0.5.RELEASE]
        ... 16 common frames omitted

As 文档中指出 https://docs.spring.io/spring/docs/current/spring-framework-reference/core.html#beans-dependency-resolution,

单例范围并设置为预实例化（默认）的 Bean 在创建容器时创建

因此，如果你把@Lazy on @Autowired，bean将在启动时创建只要bean本身没有定义lazy:

@Component
public class KafkaPublisher {
    ...
}

如果你希望这个 bean 被延迟初始化，请输入 @Lazy on it。如果你想让bean注入的过程变得懒惰，把@Lazy on @Autowired， 就如此容易。

延迟初始化一组相关的 bean 可以通过在 a 中声明它们来实现。@Configuration类别和标记配置@Lazy。但是，请注意，所有声明的 bean 将在以下情况下立即初始化：@Configuration类已初始化。

@Lazy
@Configuration
@ComponentScan(...) // will be lazily initialized with config
public class LazyConfiguration {

    @Bean
    public SomeBean beanName() { // will be lazily initialized with config
        return new SomeBean();
    } 

    @Bean
    public OtherBean beanName() { // will be lazily initialized with config
        return new OtherBean();
    }     
}

然而，当使用@ComponentScan，确保豆子（即@Service, @Component等）您想要延迟初始化尚未被其他上下文扫描。如果是，请将它们添加为扫描该上下文的排除项。

出于历史目的，下面过时的答案（在OP完全改变问题之前）：

在 beans 中声明 beans 不被认为是一个好的做法，但是如果您标记@Configuration作为惰性，那么实际上它内部的所有 bean 都会被惰性初始化，如@Lazy的javadoc：

如果 @Configuration 类上存在 Lazy，则表明所有 @Configuration 中的 @Bean 方法应该延迟初始化。

If by “里面定义的bean”你实际上指的是注入点，例如@Autowired，javadoc也有答案：

惰性注释也可以放置在标记为的注入点上 自动装配或注入：在这种情况下，它会导致创建 作为替代方案，所有受影响的依赖项的惰性解析代理 使用 ObjectFactory 或 Provider。

然而，实际的自动装配 bean 将被急切地初始化（如果也没有标记为 @Lazy）。在这种情况下，注射本身会变得懒惰。

否则，请澄清你的意思。