Spring注解驱动开发——BeanFactoryPostProcessor

BeanFactoryPostProcessor：beanFactory的后置处理器，在BeanFactory标准初始化之后调用，来定制和修改BeanFactory的内容，此时所有的bean定义已经保存并加载到beanFactory，但是bean的实例还未创建，beanFactory实际上就是spring的容器

public void refresh() throws BeansException, IllegalStateException {
	synchronized (this.startupShutdownMonitor) {
		// Prepare this context for refreshing.
		prepareRefresh();

		// Tell the subclass to refresh the internal bean factory.
		ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

		// Prepare the bean factory for use in this context.
		prepareBeanFactory(beanFactory);

		try {
			// Allows post-processing of the bean factory in context subclasses.
			postProcessBeanFactory(beanFactory);

			// Invoke factory processors registered as beans in the context.
			invokeBeanFactoryPostProcessors(beanFactory);

			// Register bean processors that intercept bean creation.
			registerBeanPostProcessors(beanFactory);

			// Initialize message source for this context.
			initMessageSource();

			// Initialize event multicaster for this context.
			initApplicationEventMulticaster();

			// Initialize other special beans in specific context subclasses.
			onRefresh();

			// Check for listener beans and register them.
			registerListeners();

			// Instantiate all remaining (non-lazy-init) singletons.
			finishBeanFactoryInitialization(beanFactory);//实例化bean

			// Last step: publish corresponding event.
			finishRefresh();
		}

		catch (BeansException ex) {
			if (logger.isWarnEnabled()) {
				logger.warn("Exception encountered during context initialization - " +
						"cancelling refresh attempt: " + ex);
			}

			// Destroy already created singletons to avoid dangling resources.
			destroyBeans();

			// Reset 'active' flag.
			cancelRefresh(ex);

			// Propagate exception to caller.
			throw ex;
		}

		finally {
			// Reset common introspection caches in Spring's core, since we
			// might not ever need metadata for singleton beans anymore...
			resetCommonCaches();
		}
	}
}

@Component
public class MyBeanFactoryPostProcessor implements BeanFactoryPostProcessor {

	@Override
	public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
		System.out.println("MyBeanFactoryPostProcessor ... postProcessBeanFactory ...");
		int count = beanFactory.getBeanDefinitionCount();
		String[] names = beanFactory.getBeanDefinitionNames();
		System.out.println("定义了:" + count + "个bean,名字是:" + Arrays.asList(names));
	}

}

BeanPostProcessor也是后置处理期，但BeanPostProcessor的调用时机是在bean创建之后，执行bean的初始化方法的前后调用其前置方法和后置方法。

Java1.8之后interface的方法在定义时也可以有方法体了，有方法体的接口方法必须使用default修饰，类似于父类：

public interface NullablIenterface {

	// @Nullable
	default void sayHello(String name) {
		System.out.println("hello" + name);
	}

	public void sayBye();
}

BeanFactoryPostProcessor的原理：

1)、ioc容器创建对象前：refresh()

     2)、invokeBeanFactoryPostProcessors(beanFactory);
        如何找到所有的BeanFactoryPostProcessor并执行他们的方法
      1）、直接在BeanFactory中找到所有类型是BeanFactoryPostProcessor的组件，并执行它们的postProcessBeanFactory方法：要求实现BeanFactoryPostProcessor接口，并且被纳入到IOC容器管理
         2）、在初始化创建其他组件前面执行：finishBeanFactoryInitialization(beanFactory);//初始化组件

Spring注解驱动开发——BeanFactoryPostProcessor

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