一次性讲清楚spring中bean的生命周期之三:bean是如何实例化的

在前面的两篇博文《一次性讲清楚spring中bean的生命周期之一:getSingleton方法》和《一次性讲清楚spring中bean的生命周期之二:FactoryBean的前世今生》中分析了spring中bean生命周期的过程中的getSingleton方法和getObjectForBeanInstance方法,今天来分析另外一个重要的方法createBean方法。分析的入口是AbstractBeanFacotry.doGetBean方法,如下图,

一次性讲清楚spring中bean的生命周期之三:bean是如何实例化的

这就是本次分析的入口。下面看该方法的详细定义,AbstractAutowireCapableBeanFactory.createBean

@Override protected Object createBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args) throws BeanCreationException { if (logger.isTraceEnabled()) { logger.trace("Creating instance of bean '" + beanName + "'"); } RootBeanDefinition mbdToUse = mbd; // Make sure bean class is actually resolved at this point, and // clone the bean definition in case of a dynamically resolved Class // which cannot be stored in the shared merged bean definition. Class<?> resolvedClass = resolveBeanClass(mbd, beanName); if (resolvedClass != null && !mbd.hasBeanClass() && mbd.getBeanClassName() != null) { mbdToUse = new RootBeanDefinition(mbd); mbdToUse.setBeanClass(resolvedClass); } // Prepare method overrides. try { mbdToUse.prepareMethodOverrides(); } catch (BeanDefinitionValidationException ex) { throw new BeanDefinitionStoreException(mbdToUse.getResourceDescription(), beanName, "Validation of method overrides failed", ex); } try { // Give BeanPostProcessors a chance to return a proxy instead of the target bean instance.
//给beanPostProcessor一个返回目标类代理类的机会 Object bean = resolveBeforeInstantiation(beanName, mbdToUse); if (bean != null) { return bean; } } catch (Throwable ex) { throw new BeanCreationException(mbdToUse.getResourceDescription(), beanName, "BeanPostProcessor before instantiation of bean failed", ex); } try {
//执行doCreatBean方法 Object beanInstance
= doCreateBean(beanName, mbdToUse, args); if (logger.isTraceEnabled()) { logger.trace("Finished creating instance of bean '" + beanName + "'"); } return beanInstance; } catch (BeanCreationException | ImplicitlyAppearedSingletonException ex) { // A previously detected exception with proper bean creation context already, // or illegal singleton state to be communicated up to DefaultSingletonBeanRegistry. throw ex; } catch (Throwable ex) { throw new BeanCreationException( mbdToUse.getResourceDescription(), beanName, "Unexpected exception during bean creation", ex); } }

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