聊聊InitDestroyAnnotationBeanPostProcessor

public interface DestructionAwareBeanPostProcessor extends BeanPostProcessor {

	/**
	 * Apply this BeanPostProcessor to the given bean instance before its
	 * destruction, e.g. invoking custom destruction callbacks.
	 * <p>Like DisposableBean's {@code destroy} and a custom destroy method, this
	 * callback will only apply to beans which the container fully manages the
	 * lifecycle for. This is usually the case for singletons and scoped beans.
	 * @param bean the bean instance to be destroyed
	 * @param beanName the name of the bean
	 * @throws org.springframework.beans.BeansException in case of errors
	 * @see org.springframework.beans.factory.DisposableBean#destroy()
	 * @see org.springframework.beans.factory.support.AbstractBeanDefinition#setDestroyMethodName(String)
	 */
	void postProcessBeforeDestruction(Object bean, String beanName) throws BeansException;

	/**
	 * Determine whether the given bean instance requires destruction by this
	 * post-processor.
	 * <p>The default implementation returns {@code true}. If a pre-5 implementation
	 * of {@code DestructionAwareBeanPostProcessor} does not provide a concrete
	 * implementation of this method, Spring silently assumes {@code true} as well.
	 * @param bean the bean instance to check
	 * @return {@code true} if {@link #postProcessBeforeDestruction} is supposed to
	 * be called for this bean instance eventually, or {@code false} if not needed
	 * @since 4.3
	 */
	default boolean requiresDestruction(Object bean) {
		return true;
	}

}

public class InitDestroyAnnotationBeanPostProcessor
		implements DestructionAwareBeanPostProcessor, MergedBeanDefinitionPostProcessor, PriorityOrdered, Serializable {

	@Nullable
	private Class<? extends Annotation> initAnnotationType;

	@Nullable
	private Class<? extends Annotation> destroyAnnotationType;

	private int order = Ordered.LOWEST_PRECEDENCE;	

	@Override
	public int getOrder() {
		return this.order;
	}


	@Override
	public void postProcessMergedBeanDefinition(RootBeanDefinition beanDefinition, Class<?> beanType, String beanName) {
		LifecycleMetadata metadata = findLifecycleMetadata(beanType);
		metadata.checkConfigMembers(beanDefinition);
	}

	@Override
	public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
		LifecycleMetadata metadata = findLifecycleMetadata(bean.getClass());
		try {
			metadata.invokeInitMethods(bean, beanName);
		}
		catch (InvocationTargetException ex) {
			throw new BeanCreationException(beanName, "Invocation of init method failed", ex.getTargetException());
		}
		catch (Throwable ex) {
			throw new BeanCreationException(beanName, "Failed to invoke init method", ex);
		}
		return bean;
	}

	@Override
	public void postProcessBeforeDestruction(Object bean, String beanName) throws BeansException {
		LifecycleMetadata metadata = findLifecycleMetadata(bean.getClass());
		try {
			metadata.invokeDestroyMethods(bean, beanName);
		}
		catch (InvocationTargetException ex) {
			String msg = "Destroy method on bean with name '" + beanName + "' threw an exception";
			if (logger.isDebugEnabled()) {
				logger.warn(msg, ex.getTargetException());
			}
			else {
				logger.warn(msg + ": " + ex.getTargetException());
			}
		}
		catch (Throwable ex) {
			logger.warn("Failed to invoke destroy method on bean with name '" + beanName + "'", ex);
		}
	}

	@Override
	public boolean requiresDestruction(Object bean) {
		return findLifecycleMetadata(bean.getClass()).hasDestroyMethods();
	}


	private LifecycleMetadata findLifecycleMetadata(Class<?> clazz) {
		if (this.lifecycleMetadataCache == null) {
			// Happens after deserialization, during destruction...
			return buildLifecycleMetadata(clazz);
		}
		// Quick check on the concurrent map first, with minimal locking.
		LifecycleMetadata metadata = this.lifecycleMetadataCache.get(clazz);
		if (metadata == null) {
			synchronized (this.lifecycleMetadataCache) {
				metadata = this.lifecycleMetadataCache.get(clazz);
				if (metadata == null) {
					metadata = buildLifecycleMetadata(clazz);
					this.lifecycleMetadataCache.put(clazz, metadata);
				}
				return metadata;
			}
		}
		return metadata;
	}	
}		

	private class LifecycleMetadata {

		private final Class<?> targetClass;

		private final Collection<LifecycleElement> initMethods;

		private final Collection<LifecycleElement> destroyMethods;

		@Nullable
		private volatile Set<LifecycleElement> checkedInitMethods;

		@Nullable
		private volatile Set<LifecycleElement> checkedDestroyMethods;

		public LifecycleMetadata(Class<?> targetClass, Collection<LifecycleElement> initMethods,
				Collection<LifecycleElement> destroyMethods) {

			this.targetClass = targetClass;
			this.initMethods = initMethods;
			this.destroyMethods = destroyMethods;
		}

		public void checkConfigMembers(RootBeanDefinition beanDefinition) {
			Set<LifecycleElement> checkedInitMethods = new LinkedHashSet<>(this.initMethods.size());
			for (LifecycleElement element : this.initMethods) {
				String methodIdentifier = element.getIdentifier();
				if (!beanDefinition.isExternallyManagedInitMethod(methodIdentifier)) {
					beanDefinition.registerExternallyManagedInitMethod(methodIdentifier);
					checkedInitMethods.add(element);
					if (logger.isTraceEnabled()) {
						logger.trace("Registered init method on class [" + this.targetClass.getName() + "]: " + element);
					}
				}
			}
			Set<LifecycleElement> checkedDestroyMethods = new LinkedHashSet<>(this.destroyMethods.size());
			for (LifecycleElement element : this.destroyMethods) {
				String methodIdentifier = element.getIdentifier();
				if (!beanDefinition.isExternallyManagedDestroyMethod(methodIdentifier)) {
					beanDefinition.registerExternallyManagedDestroyMethod(methodIdentifier);
					checkedDestroyMethods.add(element);
					if (logger.isTraceEnabled()) {
						logger.trace("Registered destroy method on class [" + this.targetClass.getName() + "]: " + element);
					}
				}
			}
			this.checkedInitMethods = checkedInitMethods;
			this.checkedDestroyMethods = checkedDestroyMethods;
		}

		public void invokeInitMethods(Object target, String beanName) throws Throwable {
			Collection<LifecycleElement> checkedInitMethods = this.checkedInitMethods;
			Collection<LifecycleElement> initMethodsToIterate =
					(checkedInitMethods != null ? checkedInitMethods : this.initMethods);
			if (!initMethodsToIterate.isEmpty()) {
				for (LifecycleElement element : initMethodsToIterate) {
					if (logger.isTraceEnabled()) {
						logger.trace("Invoking init method on bean '" + beanName + "': " + element.getMethod());
					}
					element.invoke(target);
				}
			}
		}

		public void invokeDestroyMethods(Object target, String beanName) throws Throwable {
			Collection<LifecycleElement> checkedDestroyMethods = this.checkedDestroyMethods;
			Collection<LifecycleElement> destroyMethodsToUse =
					(checkedDestroyMethods != null ? checkedDestroyMethods : this.destroyMethods);
			if (!destroyMethodsToUse.isEmpty()) {
				for (LifecycleElement element : destroyMethodsToUse) {
					if (logger.isTraceEnabled()) {
						logger.trace("Invoking destroy method on bean '" + beanName + "': " + element.getMethod());
					}
					element.invoke(target);
				}
			}
		}

		public boolean hasDestroyMethods() {
			Collection<LifecycleElement> checkedDestroyMethods = this.checkedDestroyMethods;
			Collection<LifecycleElement> destroyMethodsToUse =
					(checkedDestroyMethods != null ? checkedDestroyMethods : this.destroyMethods);
			return !destroyMethodsToUse.isEmpty();
		}
	}

public class CommonAnnotationBeanPostProcessor extends InitDestroyAnnotationBeanPostProcessor
		implements InstantiationAwareBeanPostProcessor, BeanFactoryAware, Serializable {

	public CommonAnnotationBeanPostProcessor() {
		setOrder(Ordered.LOWEST_PRECEDENCE - 3);
		setInitAnnotationType(PostConstruct.class);
		setDestroyAnnotationType(PreDestroy.class);
		ignoreResourceType("javax.xml.ws.WebServiceContext");
	}

	//......
}