@PostConstruct

initializeBean方法–> PostProcessor.postProcessBeforeInitialization–> InitDestroyAnnotationBeanPostProcessor.postProcessBeforeDestruction

被@PostConstruct注解的方法会在Bean初始化的时候被调用，如下图：

继承关系如下图：

所以到bean初始化时，会调用到InitDestroyAnnotationBeanPostProcessor.postProcessBeforeInitialization方法。

1. InitDestroyAnnotationBeanPostProcessor.postProcessBeforeInitialization–>findLifecycleMetadata->buildLifecycleMetadata
2. 通过method.isAnnotationPresent(this.initAnnotationType)判断是否有@PostConstruct，将其方法放入initMethods

 private InitDestroyAnnotationBeanPostProcessor.LifecycleMetadata buildLifecycleMetadata(Class<?> clazz) {
        if (!AnnotationUtils.isCandidateClass(clazz, Arrays.asList(this.initAnnotationType, this.destroyAnnotationType))) {
            return this.emptyLifecycleMetadata;
        } else {
            List<InitDestroyAnnotationBeanPostProcessor.LifecycleElement> initMethods = new ArrayList();
            List<InitDestroyAnnotationBeanPostProcessor.LifecycleElement> destroyMethods = new ArrayList();
            Class targetClass = clazz;

            do {
                List<InitDestroyAnnotationBeanPostProcessor.LifecycleElement> currInitMethods = new ArrayList();
                List<InitDestroyAnnotationBeanPostProcessor.LifecycleElement> currDestroyMethods = new ArrayList();
                ReflectionUtils.doWithLocalMethods(targetClass, (method) -> {
                    if (this.initAnnotationType != null && method.isAnnotationPresent(this.initAnnotationType)) {
                        InitDestroyAnnotationBeanPostProcessor.LifecycleElement element = new InitDestroyAnnotationBeanPostProcessor.LifecycleElement(method);
                        currInitMethods.add(element);
                        if (this.logger.isTraceEnabled()) {
                            this.logger.trace("Found init method on class [" + clazz.getName() + "]: " + method);
                        }
                    }

                    if (this.destroyAnnotationType != null && method.isAnnotationPresent(this.destroyAnnotationType)) {
                        currDestroyMethods.add(new InitDestroyAnnotationBeanPostProcessor.LifecycleElement(method));
                        if (this.logger.isTraceEnabled()) {
                            this.logger.trace("Found destroy method on class [" + clazz.getName() + "]: " + method);
                        }
                    }

                });
                initMethods.addAll(0, currInitMethods);
                destroyMethods.addAll(currDestroyMethods);
                targetClass = targetClass.getSuperclass();
            } while(targetClass != null && targetClass != Object.class);

            return initMethods.isEmpty() && destroyMethods.isEmpty() ? this.emptyLifecycleMetadata : new InitDestroyAnnotationBeanPostProcessor.LifecycleMetadata(clazz, initMethods, destroyMethods);
        }
    }

3. initAnnotationType在子类CommonAnnotationBeanPostProcessor的构造方法中被初始化

 public CommonAnnotationBeanPostProcessor() {
    this.setOrder(2147483644);
    this.setInitAnnotationType(PostConstruct.class);
    this.setDestroyAnnotationType(PreDestroy.class);
    this.ignoreResourceType("javax.xml.ws.WebServiceContext");
    if (jndiPresent) {
        this.jndiFactory = new SimpleJndiBeanFactory();
    }

}

4. InitDestroyAnnotationBeanPostProcessor.postProcessBeforeInitialization–>metadata.invokeDestroyMethods(bean, beanName)。在该方法中会调用被@PostConstruct注解的方法,即第二步initMethods中的方法。