8、Spring之Bean生命周期~销毁

销毁
- requiresDestruction()方法
- hasDestroyMethod()方法
- inferDestroyMethodIfNecessary()方法

销毁

AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(AppConfig.class);
UserService userService = (UserService) context.getBean("userService");
userService.test();// 容器关闭
context.close();

spring容器在正常关闭的时候会销毁Bean对象，比如上述代码中，执行close方法时，容器关闭，销毁单例的Bean对象；而销毁前回调方法的标识，是在初始化方法的doCreateBean()方法的最后一步进行的，废话不多说，上代码：

/*** 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));}}
}

通过上诉代码我们可以看到：

首先会判断不是原型Bean对象，且有销毁回调方法（判断是否存在销毁回调方法逻辑），会将DisposableBeanAdapter注册到Map<String, Object> disposableBeans中，map的key是BeanName，Value是DisposableBeanAdapter对象;

requiresDestruction()方法

requiresDestruction()方法详解

/*** Determine whether the given bean requires destruction on shutdown.* <p>The default implementation checks the DisposableBean interface as well as* a specified destroy method and registered DestructionAwareBeanPostProcessors.** @param bean the bean instance to check* @param mbd  the corresponding bean definition* @see org.springframework.beans.factory.DisposableBean* @see AbstractBeanDefinition#getDestroyMethodName()* @see org.springframework.beans.factory.config.DestructionAwareBeanPostProcessor*/
protected boolean requiresDestruction(Object bean, RootBeanDefinition mbd) {return (bean.getClass() != NullBean.class && (DisposableBeanAdapter.hasDestroyMethod(bean, mbd) ||(hasDestructionAwareBeanPostProcessors() && DisposableBeanAdapter.hasApplicableProcessors(bean, getBeanPostProcessorCache().destructionAware))));
}

通过上诉代码我们可以看到：

首先判断不是nullBean，
调用hasDestroyMethod()方法判断是否存在销毁回调方法；
调用hasDestructionAwareBeanPostProcessors()方法判断是否实现DestructionAwareBeanPostProcessor接口，如果实现了会调用会销毁前回调用法；
最后会把DisposableBeanAdapter注册进去，方便销毁时调用；

hasDestroyMethod()方法

hasDestroyMethod()方法详解

/*** 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;
}

通过上述方法，我们可以看到：

如果Bean对象实现了DisposableBean接口或者AutoCloseable接口，直接返回true
如果两个都没有实现，会调用inferDestroyMethodIfNecessary()方法，判断BeanDefinition有没有设置销毁回调方法；
回到requiresDestruction()方法；

inferDestroyMethodIfNecessary()方法

inferDestroyMethodIfNecessary()方法详解

/*** 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 DisposableBeandestroyMethodName = 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);
}