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bean销毁(找到销毁的bean)

在bean的声明周期中，存在一个记录bean销毁方法的阶段，以备于spring关闭的时候可以执行bean的销毁方法（单例bean）

v1.0 registerDisposableBeanIfNecessary

protected void registerDisposableBeanIfNecessary(String beanName, Object bean, RootBeanDefinition mbd) {AccessControlContext acc = (System.getSecurityManager() != null ? getAccessControlContext() : null);//当rootBeanDefinition不是原型bean，并且requiresDestruction方法返回true代表当前bean是需要销毁的if (!mbd.isPrototype() && requiresDestruction(bean, mbd)) {if (mbd.isSingleton()) {//最终通过适配器模式将销毁方法存入disposableBeans这个Map中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));}}}

v1.1 requiresDestruction

protected boolean requiresDestruction(Object bean, RootBeanDefinition mbd) {//首先bean不能为NULLBEAN，然后（实现了DisposableBean接口或实现了AutoCloseable） 或者有销毁的方法return (bean.getClass() != NullBean.class && (DisposableBeanAdapter.hasDestroyMethod(bean, mbd) ||(hasDestructionAwareBeanPostProcessors() && DisposableBeanAdapter.hasApplicableProcessors(bean, getBeanPostProcessorCache().destructionAware))));}

v1.2 hasDestroyMethod

public static boolean hasDestroyMethod(Object bean, RootBeanDefinition beanDefinition) {//如果实现了DisposableBean接口或实现了AutoCloseable，直接返回trueif (bean instanceof DisposableBean || bean instanceof AutoCloseable) {return true;}return inferDestroyMethodIfNecessary(bean, beanDefinition) != null;}private static String inferDestroyMethodIfNecessary(Object bean, RootBeanDefinition beanDefinition) {//从缓存中获取当前RootBeanDefinition的结束方法String destroyMethodName = beanDefinition.resolvedDestroyMethodName;if (destroyMethodName == null) {//如果缓存中没有，则尝试直接获取销毁方法名称destroyMethodName = beanDefinition.getDestroyMethodName(); ////判断bean销毁的名字是否等于(inferred)或者实现了AutoCloseable接口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;//进入这一阶段，spring会自己去寻找销毁方法if (!(bean instanceof DisposableBean)) {try {//获取类中的close方法destroyMethodName = bean.getClass().getMethod(CLOSE_METHOD_NAME).getName();}catch (NoSuchMethodException ex) {try {//获取类中的SHUTDOWN_METHOD_NAME方法destroyMethodName = bean.getClass().getMethod(SHUTDOWN_METHOD_NAME).getName();}catch (NoSuchMethodException ex2) {// no candidate destroy method found}}}}//将销毁方法名字缓存到resolvedDestroyMethodName字段中beanDefinition.resolvedDestroyMethodName = (destroyMethodName != null ? destroyMethodName : "");}return (StringUtils.hasLength(destroyMethodName) ? destroyMethodName : null);}

v1.3 hasDestructionAwareBeanPostProcessors

//判断destructionAware缓存是否为空
protected boolean hasDestructionAwareBeanPostProcessors() {return !getBeanPostProcessorCache().destructionAware.isEmpty();}BeanPostProcessorCache getBeanPostProcessorCache() {//先从缓存中拿取 BeanPostProcessorCache ，如果没获取到，说明还没有对beanPostProcessors进行分类BeanPostProcessorCache bpCache = this.beanPostProcessorCache;if (bpCache == null) {bpCache = new BeanPostProcessorCache();//对所有的beanPostProcessors进行循环分类for (BeanPostProcessor bp : this.beanPostProcessors) {if (bp instanceof InstantiationAwareBeanPostProcessor) {bpCache.instantiationAware.add((InstantiationAwareBeanPostProcessor) bp);if (bp instanceof SmartInstantiationAwareBeanPostProcessor) {bpCache.smartInstantiationAware.add((SmartInstantiationAwareBeanPostProcessor) bp);}}if (bp instanceof DestructionAwareBeanPostProcessor) {bpCache.destructionAware.add((DestructionAwareBeanPostProcessor) bp);}if (bp instanceof MergedBeanDefinitionPostProcessor) {bpCache.mergedDefinition.add((MergedBeanDefinitionPostProcessor) bp);}}this.beanPostProcessorCache = bpCache;}return bpCache;}

v1.4 DisposableBeanAdahasApplicableProcessorspter.

	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;}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 LifecycleMetadata buildLifecycleMetadata(final Class<?> clazz) {if (!AnnotationUtils.isCandidateClass(clazz, Arrays.asList(this.initAnnotationType, this.destroyAnnotationType))) {return this.emptyLifecycleMetadata;}//此处使用了双层循环处理//该集合定义了所有的初始化方法List<LifecycleElement> initMethods = new ArrayList<>();//该集合中定义了所有的销毁方法List<LifecycleElement> destroyMethods = new ArrayList<>();Class<?> targetClass = clazz;do {final List<LifecycleElement> currInitMethods = new ArrayList<>();final List<LifecycleElement> currDestroyMethods = new ArrayList<>();ReflectionUtils.doWithLocalMethods(targetClass, method -> {//判断方法是否实现了@PostConstruct注解if (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);}}//判断方法是否实现了@PreDestroy注解if (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);}}});//将父类的初始化方法放在最前面initMethods.addAll(0, currInitMethods);//将父类的销毁方法放在最后面destroyMethods.addAll(currDestroyMethods);//获取父类targetClass = targetClass.getSuperclass();}while (targetClass != null && targetClass != Object.class);return (initMethods.isEmpty() && destroyMethods.isEmpty() ? this.emptyLifecycleMetadata :new LifecycleMetadata(clazz, initMethods, destroyMethods));}

执行bean销毁

v1.1 destroySingletons

//销毁单例beanpublic void destroySingletons() {if (logger.isTraceEnabled()) {logger.trace("Destroying singletons in " + this);}synchronized (this.singletonObjects) {this.singletonsCurrentlyInDestruction = true;}String[] disposableBeanNames;synchronized (this.disposableBeans) {//获取所有有销毁方法的bean的名字disposableBeanNames = StringUtils.toStringArray(this.disposableBeans.keySet());}//遍历销毁所有的方法for (int i = disposableBeanNames.length - 1; i >= 0; i--) {destroySingleton(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);}

v1.1 destroyBean

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 {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);}