前言
前面通过 invokeBeanFactoryPostProcessors 这一步了解到了什么是 BeanFactoryPostProcessor ,以及 BeanFactoryPostProcessor 的使用及作用,并通过 invokeBeanFactoryPostProcessors 这一步源码,对 BeanFactoryPostProcessor 的加载流程有了进一步了解。
现在就一起进入下一个环节:
registerBeanPostProcessors(beanFactory);
这一步主要的作用是加载 BeanPostProcessor,从名字也可以看出,只是加载,并没有执行。
不过,在进入源码之前,依然是结合官网,先了解以下几个问题:
- 什么是 BeanPostProcessor?
- BeanPostProcessor 是如何使用的?
- BeanPostProcessor 有什么用?
什么是 BeanPostProcessor ?
如截图所示,在官网 1.8.1 Customizing Beans by Using a BeanPostProcessor 中介绍, BeanPostProcessor
接口定义回调方法,可以实现这些方法,从而在 Bean 实例化期间修改 Bean 的属性。
BeanPostProcessor 是如何使用的?
@Component public class MyBeanPostProcessor implements BeanPostProcessor { @Override public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException { if (bean instanceof UserComponent) { System.out.println("BeanPostProcessor 开始执行 初始化前..." + beanName); UserComponent userComponent = (UserComponent) bean; userComponent.setUserName("liuzhihang-postProcessBeforeInitialization"); return userComponent; } return bean; } @Override public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException { if (bean instanceof UserComponent) { System.out.println("BeanPostProcessor 开始执行 初始化后..." + beanName); UserComponent userComponent = (UserComponent) bean; userComponent.setUserName("liuzhihang-postProcessAfterInitialization"); return userComponent; } return bean; } }
如代码所示,只需要声明一个自己的 MyBeanPostProcessor 来实现 BeanPostProcessor
并重写其方法:
postProcessBeforeInitialization :在 Bean 实例后调用初始化方法之前进行处理。
postProcessAfterInitialization :在 Bean 实例化后调用初始化方法之后进行处理。
并且在测试时可以发现,BeanPostProcessor 修改的属性会覆盖
BeanFactoryPostProcessor,至于原因可以阅读下 Spring 源码学习 11:invokeBeanFactoryPostProcessors 这篇文章,相信对 BeanFactoryPostProcessor 有了一定的了解之后,一定会有自己的答案。
当然我个人的理解就是 BeanFactoryPostProcessor 是在 Bean 实例化之前,是通过修改元数据从而修改的 Bean 的元素信息。
这块也可以通过代码进行验证。
可以看出,执行顺序是
BeanFactoryPostProcessor#postProcessBeanFactory
->BeanPostProcessor#postProcessBeforeInitialization
->BeanPostProcessor#postProcessAfterInitialization
所以,后面修改的属性,会覆盖之前修改的属性。
至于 BeanPostProcessor
是如何修改属性的,在这里先不做介绍,继续进入本节的主角 registerBeanPostProcessors 源码分析
registerBeanPostProcessors 源码
在 Spring refresh 方法中,执行 registerBeanPostProcessors 主要作用是将 BeanPostProcessor 注册到容器中,源码如下:
protected void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory) { PostProcessorRegistrationDelegate.registerBeanPostProcessors(beanFactory, this); }
这里调用了 PostProcessorRegistrationDelegate
类的静态方法,继续跟进:
public static void registerBeanPostProcessors( ConfigurableListableBeanFactory beanFactory, AbstractApplicationContext applicationContext) { // 查找 BeanPostProcessor 类型的 Bean 的名称集合, 就是获取所有继承了 BeanPostProcessor 的类 String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false); // Register BeanPostProcessorChecker that logs an info message when // a bean is created during BeanPostProcessor instantiation, i.e. when // a bean is not eligible for getting processed by all BeanPostProcessors. // 注册一个 BeanPostProcessorChecker,用来记录 bean 在 BeanPostProcessor 实例化时的信息。 int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length; beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount)); // Separate between BeanPostProcessors that implement PriorityOrdered, // Ordered, and the rest. // 四个集合 区分实现不同接口的 BeanPostProcessors List<BeanPostProcessor> priorityOrderedPostProcessors = new ArrayList<>(); List<BeanPostProcessor> internalPostProcessors = new ArrayList<>(); List<String> orderedPostProcessorNames = new ArrayList<>(); List<String> nonOrderedPostProcessorNames = new ArrayList<>(); for (String ppName : postProcessorNames) { if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) { BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class); priorityOrderedPostProcessors.add(pp); if (pp instanceof MergedBeanDefinitionPostProcessor) { internalPostProcessors.add(pp); } } else if (beanFactory.isTypeMatch(ppName, Ordered.class)) { orderedPostProcessorNames.add(ppName); } else { nonOrderedPostProcessorNames.add(ppName); } } // First, register the BeanPostProcessors that implement PriorityOrdered. // 排序后执行 实现 PriorityOrdered 的 BeanPostProcessors sortPostProcessors(priorityOrderedPostProcessors, beanFactory); registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors); // Next, register the BeanPostProcessors that implement Ordered. List<BeanPostProcessor> orderedPostProcessors = new ArrayList<>(orderedPostProcessorNames.size()); for (String ppName : orderedPostProcessorNames) { BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class); orderedPostProcessors.add(pp); if (pp instanceof MergedBeanDefinitionPostProcessor) { internalPostProcessors.add(pp); } } sortPostProcessors(orderedPostProcessors, beanFactory); registerBeanPostProcessors(beanFactory, orderedPostProcessors); // Now, register all regular BeanPostProcessors. List<BeanPostProcessor> nonOrderedPostProcessors = new ArrayList<>(nonOrderedPostProcessorNames.size()); for (String ppName : nonOrderedPostProcessorNames) { BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class); nonOrderedPostProcessors.add(pp); if (pp instanceof MergedBeanDefinitionPostProcessor) { internalPostProcessors.add(pp); } } registerBeanPostProcessors(beanFactory, nonOrderedPostProcessors); // Finally, re-register all internal BeanPostProcessors. sortPostProcessors(internalPostProcessors, beanFactory); registerBeanPostProcessors(beanFactory, internalPostProcessors); // Re-register post-processor for detecting inner beans as ApplicationListeners, // moving it to the end of the processor chain (for picking up proxies etc). beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(applicationContext)); }
代码中添加了相应的注释,相信读过上一篇文章(invokeBeanFactoryPostProcessors 源码)的小伙伴,一定会感觉非常熟悉,这个方法的逻辑和上面基本一致,都是声明集合,排序,注册到 BeanFactory 中。
不过还是有区别的:
registerBeanPostProcessors 这一步仅仅将 BeanPostProcessor 注册到 BeanFactory 中,并没有执行!!!
总结
本文源码部分相对比较简单,主要花费部分篇幅介绍什么是 BeanPostProcessor 以及 BeanPostProcessor 的使用方法。
一句话总结这一步就是:注册 BeanPostProcessor 到 BeanFactory 中,但是没有执行。