spring-ioc 部分interface接口

• 内容
• apis
  • SmartInitializingSingleton
    • 类注释
    • 方法注释
  • 调用过程
    • 场景及实例

内容

介绍部分ioc中的接口功能及其使用场景

apis

SmartInitializingSingleton

所有单例bean初始化完成后调用

类注释

• Callback interface triggered at the end of the singleton pre-instantiation phase
• during {@link BeanFactory} bootstrap. This interface can be implemented by
• singleton beans in order to perform some initialization after the regular
• singleton instantiation algorithm, avoiding side effects with accidental early
• initialization (e.g. from {@link ListableBeanFactory#getBeansOfType} calls).
• In that sense, it is an alternative to {@link InitializingBean} which gets
• triggered right at the end of a bean’s local construction phase.

• This callback variant is somewhat similar to

• {@link org.springframework.context.event.ContextRefreshedEvent} but doesn’t
• require an implementation of {@link org.springframework.context.ApplicationListener},
• with no need to filter context references across a context hierarchy etc.
• It also implies a more minimal dependency on just the {@code beans} package
• and is being honored by standalone {@link ListableBeanFactory} implementations,
• not just in an {@link org.springframework.context.ApplicationContext} environment.

• NOTE: If you intend to start/manage asynchronous tasks, preferably

• implement {@link org.springframework.context.Lifecycle} instead which offers
• a richer model for runtime management and allows for phased startup/shutdown.

方法注释

• Invoked right at the end of the singleton pre-instantiation phase,
• with a guarantee that all regular singleton beans have been created
• already. {@link ListableBeanFactory#getBeansOfType} calls within
• this method won’t trigger accidental side effects during bootstrap.

• NOTE: This callback won't be triggered for singleton beans

• lazily initialized on demand after {@link BeanFactory} bootstrap,
• and not for any other bean scope either. Carefully use it for beans
• with the intended bootstrap semantics only.

调用过程

ApplicationContext 在 refresh 过程中会调用 finishBeanFactoryInitialization(beanFactory) 来提前初始化单例bean，具体方法是调用 preInstantiateSingletons，
该方法定义在接口 ConfigurableListableBeanFactory 中。

public void preInstantiateSingletons() throws BeansException {
    if (logger.isDebugEnabled()) {
        logger.debug("Pre-instantiating singletons in " + this);
    }

    // Iterate over a copy to allow for init methods which in turn register new bean definitions.
    // While this may not be part of the regular factory bootstrap, it does otherwise work fine.
    List<String> beanNames = new ArrayList<>(this.beanDefinitionNames);

    // Trigger initialization of all non-lazy singleton beans...
    for (String beanName : beanNames) {
        RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
        if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
            if (isFactoryBean(beanName)) {
                Object bean = getBean(FACTORY_BEAN_PREFIX + beanName);
                if (bean instanceof FactoryBean) {
                    final FactoryBean<?> factory = (FactoryBean<?>) bean;
                    boolean isEagerInit;
                    if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {
                        isEagerInit = AccessController.doPrivileged((PrivilegedAction<Boolean>)
                                        ((SmartFactoryBean<?>) factory)::isEagerInit,
                                getAccessControlContext());
                    }
                    else {
                        isEagerInit = (factory instanceof SmartFactoryBean &&
                                ((SmartFactoryBean<?>) factory).isEagerInit());
                    }
                    if (isEagerInit) {
                        getBean(beanName);
                    }
                }
            }
            else {
                getBean(beanName);
            }
        }
    }

    // Trigger post-initialization callback for all applicable beans...
    for (String beanName : beanNames) {
        Object singletonInstance = getSingleton(beanName);
        if (singletonInstance instanceof SmartInitializingSingleton) {
            final SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance;
            if (System.getSecurityManager() != null) {
                AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
                    smartSingleton.afterSingletonsInstantiated();
                    return null;
                }, getAccessControlContext());
            }
            else {
                smartSingleton.afterSingletonsInstantiated();
            }
        }
    }
}

场景及实例

spring boot rocketmq中，ListenerContainerConfiguration 实现ApplicationContextAware, SmartInitializingSingleton两个接口，将MQListenerContainer注册到了spring中