在getBean方法中,getObjectForBeanInstance是个高频率使用的方法,无论是从缓存中获得bean还是根据不同的scope策略加载bean。总之,我们得到bean的实例后要做的第一步就是调用这个方法来检测一下正确性,其实就是用于检测当前bean是否是FactoryBean类型的bean,如果是,那么需要调用该bean对应的FactoryBean实例中的getObject()作为返回值。
无论是否是从缓存中获取到的bean还是通过不同的scope策略加载的bean都只是最原始的bean状态,并不一定是我们最终想要的bean。我们真正需要的是工厂bean中定义的factory-method方法中返回的bean,而getObjectForBeanInstance方法就是完成这个工作的。
protected Object getObjectForBeanInstance( Object beanInstance, String name, String beanName, RootBeanDefinition mbd) { // Don't let calling code try to dereference the factory if the bean isn't a factory. if (BeanFactoryUtils.isFactoryDereference(name) && !(beanInstance instanceof FactoryBean)) { throw new BeanIsNotAFactoryException(transformedBeanName(name), beanInstance.getClass()); } // Now we have the bean instance, which may be a normal bean or a FactoryBean. // If it's a FactoryBean, we use it to create a bean instance, unless the // caller actually wants a reference to the factory. if (!(beanInstance instanceof FactoryBean) || BeanFactoryUtils.isFactoryDereference(name)) { return beanInstance; } Object object = null; if (mbd == null) { object = getCachedObjectForFactoryBean(beanName); } if (object == null) { // Return bean instance from factory. FactoryBean<?> factory = (FactoryBean<?>) beanInstance; // Caches object obtained from FactoryBean if it is a singleton. if (mbd == null && containsBeanDefinition(beanName)) { mbd = getMergedLocalBeanDefinition(beanName); } boolean synthetic = (mbd != null && mbd.isSynthetic()); object = getObjectFromFactoryBean(factory, beanName, !synthetic); } return object; }
getObjectForBeanInstance中所作的工作:
(1)对FactoryBean正确性的验证
(2)对非FactoryBean不做任何处理
(3)对bean进行转换
(4)将从Factory中解析bean的工作委托给getObjectFromFactoryBean
protected Object getObjectFromFactoryBean(FactoryBean<?> factory, String beanName, boolean shouldPostProcess) { if (factory.isSingleton() && containsSingleton(beanName)) { synchronized (getSingletonMutex()) { Object object = this.factoryBeanObjectCache.get(beanName); if (object == null) { object = doGetObjectFromFactoryBean(factory, beanName, shouldPostProcess); this.factoryBeanObjectCache.put(beanName, (object != null ? object : NULL_OBJECT)); } return (object != NULL_OBJECT ? object : null); } } else { return doGetObjectFromFactoryBean(factory, beanName, shouldPostProcess); } }
在这个方法里只做了一件事,就是返回的bean如果是单例的,那就必须保证全局唯一。
private Object doGetObjectFromFactoryBean( final FactoryBean<?> factory, final String beanName, final boolean shouldPostProcess) throws BeanCreationException { Object object; try { if (System.getSecurityManager() != null) { AccessControlContext acc = getAccessControlContext(); try { object = AccessController.doPrivileged(new PrivilegedExceptionAction<Object>() { public Object run() throws Exception { return factory.getObject(); } }, acc); } catch (PrivilegedActionException pae) { throw pae.getException(); } } else { object = factory.getObject(); } } catch (FactoryBeanNotInitializedException ex) { throw new BeanCurrentlyInCreationException(beanName, ex.toString()); } catch (Throwable ex) { throw new BeanCreationException(beanName, "FactoryBean threw exception on object creation", ex); } // Do not accept a null value for a FactoryBean that's not fully // initialized yet: Many FactoryBeans just return null then. if (object == null && isSingletonCurrentlyInCreation(beanName)) { throw new BeanCurrentlyInCreationException( beanName, "FactoryBean which is currently in creation returned null from getObject"); } if (object != null && shouldPostProcess) { try { object = postProcessObjectFromFactoryBean(object, beanName); } catch (Throwable ex) { throw new BeanCreationException(beanName, "Post-processing of the FactoryBean's object failed", ex); } } return object; }
跟踪进行AbstractAutowireCapableBeanFactory类的postProcessObjectFromFactoryBean方法:
protected Object postProcessObjectFromFactoryBean(Object object, String beanName) { return applyBeanPostProcessorsAfterInitialization(object, beanName); }
public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName) throws BeansException { Object result = existingBean; for (BeanPostProcessor beanProcessor : getBeanPostProcessors()) { result = beanProcessor.postProcessAfterInitialization(result, beanName); if (result == null) { return result; } } return result; }对于后处理器的使用还未过多接触,spring在获取bean的规则中有这样一条:尽可能保证所有bean初始化后都会调用注册的BeanPostProcessor的postProcessAfterInitialization方法进行处理。