spring-bean的销毁流程

1 引入

在 Spring 框架中，Bean 的生命周期管理是其核心功能之一，而 Bean 的注销（Destruction）是生命周期的最后一步。无论是关闭数据库连接、释放线程资源，还是执行缓存持久化操作，合适的销毁策略都至关重要。Spring 为 Bean 提供了多种注销方式，包括实现特定接口、注解配置和 XML 配置等，同时通过源码设计保证了销毁操作的安全性和灵活性。本文将深入剖析 Spring Bean 注销的原理和实现细节，并结合源码探讨其调用流程和应用场景。

2 销毁方法的注册

2.1 入口

核心类：AbstractBeanFactory.java 核心方法：registerDisposableBeanIfNecessary

protected void registerDisposableBeanIfNecessary(String beanName, Object bean, RootBeanDefinition mbd) {AccessControlContext acc = (System.getSecurityManager() != null ? getAccessControlContext() : null);// 单例bean并且是否配置了注销方法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.//注册注销方法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));}}
}

2.2 销毁方法的判断

protected boolean requiresDestruction(Object bean, RootBeanDefinition mbd) {// bean不能为nullBean// 是否实现DisposableBean接口或者AutoCloseable接口// 是否配置了关于bean销毁的BeanPostProcessorreturn (bean.getClass() != NullBean.class && (DisposableBeanAdapter.hasDestroyMethod(bean, mbd) ||(hasDestructionAwareBeanPostProcessors() && DisposableBeanAdapter.hasApplicableProcessors(bean, getBeanPostProcessorCache().destructionAware))));
}

2.2.1 DisposableBean接口或者AutoCloseable接口

public static boolean hasDestroyMethod(Object bean, RootBeanDefinition beanDefinition) {if (bean instanceof DisposableBean || bean instanceof AutoCloseable) {return true;}// 推断注销方法return inferDestroyMethodIfNecessary(bean, beanDefinition) != null;
}private static String inferDestroyMethodIfNecessary(Object bean, RootBeanDefinition beanDefinition) {String destroyMethodName = beanDefinition.resolvedDestroyMethodName;if (destroyMethodName == null) {destroyMethodName = beanDefinition.getDestroyMethodName();// 如果配置的销毁方法名为(inferred) 或者实现了AutoCloseable接口 或者没有配置销毁方法名称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 DisposableBeandestroyMethodName = null;if (!(bean instanceof DisposableBean)) {try {// 是否配置了名为close的方法destroyMethodName = bean.getClass().getMethod(CLOSE_METHOD_NAME).getName();}catch (NoSuchMethodException ex) {try {// 是否配置了名为shutdown方法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);
}

2.2.2 DestructionAwareBeanPostProcessor

public static boolean hasApplicableProcessors(Object bean, List<DestructionAwareBeanPostProcessor> postProcessors) {if (!CollectionUtils.isEmpty(postProcessors)) {for (DestructionAwareBeanPostProcessor processor : postProcessors) {if (processor.requiresDestruction(bean)) {return true;}}}return false;
}//实现类：InitDestroyAnnotationBeanPostProcessor.java
public boolean requiresDestruction(Object bean) {// 判断是否配置了bean销毁的后置处理器return findLifecycleMetadata(bean.getClass()).hasDestroyMethods();
}private LifecycleMetadata findLifecycleMetadata(Class<?> clazz) {// 缓存中没有 就去构建一份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 LifecycleMetadata buildLifecycleMetadata(final Class<?> clazz) {if (!AnnotationUtils.isCandidateClass(clazz, Arrays.asList(this.initAnnotationType, this.destroyAnnotationType))) {return this.emptyLifecycleMetadata;}List<LifecycleElement> initMethods = new ArrayList<>();List<LifecycleElement> destroyMethods = new ArrayList<>();Class<?> targetClass = clazz;do {final List<LifecycleElement> currInitMethods = new ArrayList<>();final List<LifecycleElement> currDestroyMethods = new ArrayList<>();// 遍历方法ReflectionUtils.doWithLocalMethods(targetClass, method -> {// 判断是否存在@postConstructif (this.initAnnotationType != null && method.isAnnotationPresent(this.initAnnotationType)) {LifecycleElement element = new LifecycleElement(method);currInitMethods.add(element);if (logger.isTraceEnabled()) {logger.trace("Found init method on class [" + clazz.getName() + "]: " + method);}}// 判断是否存在@PreDestroyif (this.destroyAnnotationType != null && method.isAnnotationPresent(this.destroyAnnotationType)) {currDestroyMethods.add(new LifecycleElement(method));if (logger.isTraceEnabled()) {logger.trace("Found destroy method on class [" + clazz.getName() + "]: " + method);}}});// 父类的在前面initMethods.addAll(0, currInitMethods);destroyMethods.addAll(currDestroyMethods);// 遍历父类targetClass = targetClass.getSuperclass();}while (targetClass != null && targetClass != Object.class);return (initMethods.isEmpty() && destroyMethods.isEmpty() ? this.emptyLifecycleMetadata :new LifecycleMetadata(clazz, initMethods, destroyMethods));
}

3 执行销毁方法

核心类：AbstractApplicationContext.java 核心方法：doClose

protected void doClose() {// Check whether an actual close attempt is necessary...if (this.active.get() && this.closed.compareAndSet(false, true)) {if (logger.isDebugEnabled()) {logger.debug("Closing " + this);}if (!NativeDetector.inNativeImage()) {LiveBeansView.unregisterApplicationContext(this);}try {// Publish shutdown event.publishEvent(new ContextClosedEvent(this));}catch (Throwable ex) {logger.warn("Exception thrown from ApplicationListener handling ContextClosedEvent", ex);}// Stop all Lifecycle beans, to avoid delays during individual destruction.if (this.lifecycleProcessor != null) {try {this.lifecycleProcessor.onClose();}catch (Throwable ex) {logger.warn("Exception thrown from LifecycleProcessor on context close", ex);}}// Destroy all cached singletons in the context's BeanFactory.//销毁所有的beandestroyBeans();// Close the state of this context itself.closeBeanFactory();// Let subclasses do some final clean-up if they wish...onClose();// Reset local application listeners to pre-refresh state.if (this.earlyApplicationListeners != null) {this.applicationListeners.clear();this.applicationListeners.addAll(this.earlyApplicationListeners);}// Switch to inactive.this.active.set(false);}
}protected void destroyBeans() {getBeanFactory().destroySingletons();
}public void destroySingletons() {if (logger.isTraceEnabled()) {logger.trace("Destroying singletons in " + this);}synchronized (this.singletonObjects) {this.singletonsCurrentlyInDestruction = true;}String[] disposableBeanNames;synchronized (this.disposableBeans) {disposableBeanNames = StringUtils.toStringArray(this.disposableBeans.keySet());}for (int i = disposableBeanNames.length - 1; i >= 0; i--) {// 销毁beandestroySingleton(disposableBeanNames[i]);}this.containedBeanMap.clear();this.dependentBeanMap.clear();this.dependenciesForBeanMap.clear();clearSingletonCache();
}public void destroySingleton(String beanName) {// Remove a registered singleton of the given name, if any.// 先从单例池中移除掉removeSingleton(beanName);// Destroy the corresponding DisposableBean instance.DisposableBean disposableBean;synchronized (this.disposableBeans) {disposableBean = (DisposableBean) this.disposableBeans.remove(beanName);}destroyBean(beanName, disposableBean);
}protected void destroyBean(String beanName, @Nullable DisposableBean bean) {// dependentBeanMap表示某bean被哪些bean依赖了// 所以现在要销毁某个bean时，如果这个Bean还被其他Bean依赖了，那么也得销毁其他Bean// Trigger destruction of dependent beans first...Set<String> dependencies;synchronized (this.dependentBeanMap) {// Within full synchronization in order to guarantee a disconnected Setdependencies = this.dependentBeanMap.remove(beanName);}if (dependencies != null) {if (logger.isTraceEnabled()) {logger.trace("Retrieved dependent beans for bean '" + beanName + "': " + dependencies);}for (String dependentBeanName : dependencies) {destroySingleton(dependentBeanName);}}// Actually destroy the bean now...if (bean != null) {try {// 调用销毁方法bean.destroy();}catch (Throwable ex) {if (logger.isWarnEnabled()) {logger.warn("Destruction of bean with name '" + beanName + "' threw an exception", ex);}}}// Trigger destruction of contained beans...Set<String> containedBeans;synchronized (this.containedBeanMap) {// Within full synchronization in order to guarantee a disconnected SetcontainedBeans = this.containedBeanMap.remove(beanName);}if (containedBeans != null) {for (String containedBeanName : containedBeans) {destroySingleton(containedBeanName);}}// Remove destroyed bean from other beans' dependencies.synchronized (this.dependentBeanMap) {for (Iterator<Map.Entry<String, Set<String>>> it = this.dependentBeanMap.entrySet().iterator(); it.hasNext();) {Map.Entry<String, Set<String>> entry = it.next();Set<String> dependenciesToClean = entry.getValue();dependenciesToClean.remove(beanName);if (dependenciesToClean.isEmpty()) {it.remove();}}}// Remove destroyed bean's prepared dependency information.this.dependenciesForBeanMap.remove(beanName);
}//实现类：DisposableBeanAdapter.java
public void destroy() {if (!CollectionUtils.isEmpty(this.beanPostProcessors)) {// 如果类型是DestructionAwareBeanPostProcessorfor (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 {// 实现了DisposableBean接口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);}}}// 执行推断的销毁方法if (this.destroyMethod != null) {invokeCustomDestroyMethod(this.destroyMethod);}else if (this.destroyMethodName != null) {Method methodToInvoke = determineDestroyMethod(this.destroyMethodName);if (methodToInvoke != null) {invokeCustomDestroyMethod(ClassUtils.getInterfaceMethodIfPossible(methodToInvoke));}}
}

4 总结

1. 在bean初始化后 会执行销毁方法的注册 注册主要分为两类 一类是实现接口 一类是通过bean的后置处理器

2. 实现DisposableBean接口或者AutoCloseable接口 会直接注册

3. 如果配置了DestructionAwareBeanPostProcessor 并且校验方法返回true 也会添加到注册流程

4. 在容器关闭时 会注销bean 注销时会将注册bean的销毁方法容器取出遍历执行对应的销毁方法