@PostConstruct

initializeBean方法–> PostProcessor.postProcessMergedBeanDefinition --> 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.postProcessBeforeDestruction方法。

1. InitDestroyAnnotationBeanPostProcessor.postProcessMergedBeanDefinition -->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.postProcessMergedBeanDefinition -->metadata.invokeDestroyMethods(bean, beanName)。在该方法中会调用被@PostConstruct注解的方法