注册销毁方法

// Register bean as disposable.
try {
    // 注册销毁的方法
    registerDisposableBeanIfNecessary(beanName, bean, mbd);
} catch (BeanDefinitionValidationException ex) {
    throw new BeanCreationException(
            mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex);
}

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, getBeanPostProcessors(), 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, getBeanPostProcessors(), acc));
        }
    }
}

Spring 中不但提供了对于初始化方法的扩展入口，同样也提供了销毁方法的扩展入口，对于销毁方法的扩展，除了我们熟知的配置属性 destroy-method 方法外，用户还可以注册后处理器 DestructionAwareBeanPostProcessor 来统一处理 bean 的销毁方法。