PS: 查看源碼的jar版本為 Spring-beans:5.2.15.release

普通Bean的初始化是在容器啟動(dòng)初始化階段執(zhí)行的，而被lazy-init=true修飾的bean則是從容器第一次進(jìn)行context.getBean()進(jìn)行觸發(fā)。Spring啟動(dòng)的時(shí)候會(huì)把所有bean信息（包括XML和注解）解析轉(zhuǎn)化為Spring能夠識(shí)別的BeanDefinition并存到HashMap里供下面的初始化時(shí)用，然后會(huì)對(duì)每個(gè)BeanDefinition進(jìn)行從處理，如果時(shí)懶加載的則在容器初始化階段不處理，其他的則在容器初始化階段進(jìn)行初始化并依賴注入。

    @Override
    public void preInstantiateSingletons() throws BeansException {
        if (logger.isTraceEnabled()) {
            logger.trace("Pre-instantiating singletons in " + this);
        }

        //所有beanDefinition集合
        List<String> beanNames = new ArrayList<>(this.beanDefinitionNames);

        // 觸發(fā)所有非懶加載單例bean的初始化
        for (String beanName : beanNames) {
            //獲取bean定義
            RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
            //判斷是否是懶加載單例bean，如果是單例的并且不是懶加載的則在容器創(chuàng)建時(shí)初始化
            if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
                //判斷是否 FactoryBean
                if (isFactoryBean(beanName)) {
                    Object bean = getBean(FACTORY_BEAN_PREFIX + beanName);
                    if (bean instanceof FactoryBean) {
                        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 {
/*
如果普通bean則進(jìn)行初始化并依賴注入，getBean(beanName)接下來(lái)觸發(fā)的邏輯和懶加載時(shí) 
context.getBean("beanName") 所觸發(fā)的邏輯是?樣的
*/                  getBean(beanName);
                }
            }
        }
...
}

• 總結(jié)
  • 對(duì)于被修飾為lazy-init的bean Spring容器初始化階段不會(huì)進(jìn)行init并且依賴注入，當(dāng)?shù)谝淮蝕etBean時(shí)候才會(huì)進(jìn)行初始化并依賴注入
  • 對(duì)于非懶加載的bean，getBean的時(shí)候會(huì)從緩存里獲取，因?yàn)槿萜鞒跏蓟A段Bean已經(jīng)初始胡完成并緩存起來(lái)了