聊聊DisposableBeanAdapter

public interface DisposableBean {

	/**
	 * Invoked by the containing {@code BeanFactory} on destruction of a bean.
	 * @throws Exception in case of shutdown errors. Exceptions will get logged
	 * but not rethrown to allow other beans to release their resources as well.
	 */
	void destroy() throws Exception;

}

class DisposableBeanAdapter implements DisposableBean, Runnable, Serializable {

	private static final String CLOSE_METHOD_NAME = "close";

	private static final String SHUTDOWN_METHOD_NAME = "shutdown";

	private static final Log logger = LogFactory.getLog(DisposableBeanAdapter.class);


	private final Object bean;

	private final String beanName;

	private final boolean invokeDisposableBean;

	private final boolean nonPublicAccessAllowed;

	@Nullable
	private final AccessControlContext acc;

	@Nullable
	private String destroyMethodName;

	@Nullable
	private transient Method destroyMethod;

	@Nullable
	private final List<DestructionAwareBeanPostProcessor> beanPostProcessors;

	@Override
	public void run() {
		destroy();
	}

	@Override
	public void destroy() {
		if (!CollectionUtils.isEmpty(this.beanPostProcessors)) {
			for (DestructionAwareBeanPostProcessor processor : this.beanPostProcessors) {
				processor.postProcessBeforeDestruction(this.bean, this.beanName);
			}
		}

		if (this.invokeDisposableBean) {
			if (logger.isTraceEnabled()) {
				logger.trace("Invoking destroy() on bean with name '" + this.beanName + "'");
			}
			try {
				if (System.getSecurityManager() != null) {
					AccessController.doPrivileged((PrivilegedExceptionAction<Object>) () -> {
						((DisposableBean) this.bean).destroy();
						return null;
					}, this.acc);
				}
				else {
					((DisposableBean) this.bean).destroy();
				}
			}
			catch (Throwable ex) {
				String msg = "Invocation of destroy method failed on bean with name '" + this.beanName + "'";
				if (logger.isDebugEnabled()) {
					logger.warn(msg, ex);
				}
				else {
					logger.warn(msg + ": " + ex);
				}
			}
		}

		if (this.destroyMethod != null) {
			invokeCustomDestroyMethod(this.destroyMethod);
		}
		else if (this.destroyMethodName != null) {
			Method methodToInvoke = determineDestroyMethod(this.destroyMethodName);
			if (methodToInvoke != null) {
				invokeCustomDestroyMethod(ClassUtils.getInterfaceMethodIfPossible(methodToInvoke));
			}
		}
	}

	/**
	 * Check whether the given bean has any kind of destroy method to call.
	 * @param bean the bean instance
	 * @param beanDefinition the corresponding bean definition
	 */
	public static boolean hasDestroyMethod(Object bean, RootBeanDefinition beanDefinition) {
		if (bean instanceof DisposableBean || bean instanceof AutoCloseable) {
			return true;
		}
		return inferDestroyMethodIfNecessary(bean, beanDefinition) != null;
	}

	/**
	 * If the current value of the given beanDefinition's "destroyMethodName" property is
	 * {@link AbstractBeanDefinition#INFER_METHOD}, then attempt to infer a destroy method.
	 * Candidate methods are currently limited to public, no-arg methods named "close" or
	 * "shutdown" (whether declared locally or inherited). The given BeanDefinition's
	 * "destroyMethodName" is updated to be null if no such method is found, otherwise set
	 * to the name of the inferred method. This constant serves as the default for the
	 * {@code @Bean#destroyMethod} attribute and the value of the constant may also be
	 * used in XML within the {@code <bean destroy-method="">} or {@code
	 * <beans default-destroy-method="">} attributes.
	 * <p>Also processes the {@link java.io.Closeable} and {@link java.lang.AutoCloseable}
	 * interfaces, reflectively calling the "close" method on implementing beans as well.
	 */
	@Nullable
	private static String inferDestroyMethodIfNecessary(Object bean, RootBeanDefinition beanDefinition) {
		String destroyMethodName = beanDefinition.resolvedDestroyMethodName;
		if (destroyMethodName == null) {
			destroyMethodName = beanDefinition.getDestroyMethodName();
			if (AbstractBeanDefinition.INFER_METHOD.equals(destroyMethodName) ||
					(destroyMethodName == null && bean instanceof AutoCloseable)) {
				// Only perform destroy method inference or Closeable detection
				// in case of the bean not explicitly implementing DisposableBean
				destroyMethodName = null;
				if (!(bean instanceof DisposableBean)) {
					try {
						destroyMethodName = bean.getClass().getMethod(CLOSE_METHOD_NAME).getName();
					}
					catch (NoSuchMethodException ex) {
						try {
							destroyMethodName = bean.getClass().getMethod(SHUTDOWN_METHOD_NAME).getName();
						}
						catch (NoSuchMethodException ex2) {
							// no candidate destroy method found
						}
					}
				}
			}
			beanDefinition.resolvedDestroyMethodName = (destroyMethodName != null ? destroyMethodName : "");
		}
		return (StringUtils.hasLength(destroyMethodName) ? destroyMethodName : null);
	}	
}	

	/**
	 * Add the given bean to the list of disposable beans in this factory,
	 * registering its DisposableBean interface and/or the given destroy method
	 * to be called on factory shutdown (if applicable). Only applies to singletons.
	 * @param beanName the name of the bean
	 * @param bean the bean instance
	 * @param mbd the bean definition for the bean
	 * @see RootBeanDefinition#isSingleton
	 * @see RootBeanDefinition#getDependsOn
	 * @see #registerDisposableBean
	 * @see #registerDependentBean
	 */
	protected void registerDisposableBeanIfNecessary(String beanName, Object bean, RootBeanDefinition mbd) {
		AccessControlContext acc = (System.getSecurityManager() != null ? getAccessControlContext() : null);
		if (!mbd.isPrototype() && requiresDestruction(bean, mbd)) {
			if (mbd.isSingleton()) {
				// Register a DisposableBean implementation that performs all destruction
				// work for the given bean: DestructionAwareBeanPostProcessors,
				// DisposableBean interface, custom destroy method.
				registerDisposableBean(beanName, new DisposableBeanAdapter(
						bean, beanName, mbd, getBeanPostProcessorCache().destructionAware, acc));
			}
			else {
				// A bean with a custom scope...
				Scope scope = this.scopes.get(mbd.getScope());
				if (scope == null) {
					throw new IllegalStateException("No Scope registered for scope name '" + mbd.getScope() + "'");
				}
				scope.registerDestructionCallback(beanName, new DisposableBeanAdapter(
						bean, beanName, mbd, getBeanPostProcessorCache().destructionAware, acc));
			}
		}
	}

	protected boolean requiresDestruction(Object bean, RootBeanDefinition mbd) {
		return (bean.getClass() != NullBean.class && (DisposableBeanAdapter.hasDestroyMethod(bean, mbd) ||
				(hasDestructionAwareBeanPostProcessors() && DisposableBeanAdapter.hasApplicableProcessors(
						bean, getBeanPostProcessorCache().destructionAware))));
	}