上一节讲到bean初始化方法initializeBean方法的第一步，invokeAwareMethods。
这节将初始化bean的第二步，applyBeanPostProcessorsBeforeInitialization方法
看代码实现：
遍历beanFactory里面的beanPostProcessor，执行postProcessBeforeInitialization方法，
/** * factory的回调，允许用户自定义bean * Factory hook that allows for custom modification of new bean instances, * e.g. checking for marker interfaces or wrapping them with proxies. * applicationContext 可以自己注入新的beanPostProcessor用来改造bean * <p>ApplicationContexts can autodetect BeanPostProcessor beans in their * bean definitions and apply them to any beans subsequently created. * Plain bean factories allow for programmatic registration of post-processors, * applying to all beans created through this factory. * 一般是在postProcessAfterInitiazation方法中使用代理包装bean * <p>Typically, post-processors that populate beans via marker interfaces * or the like will implement {@link #postProcessBeforeInitialization}, * while post-processors that wrap beans with proxies will normally * implement {@link #postProcessAfterInitialization}. */ public interface BeanPostProcessor { /** * Apply this BeanPostProcessor to the given new bean instance <i>before</i> any bean * initialization callbacks (like InitializingBean's {@code afterPropertiesSet} * or a custom init-method). The bean will already be populated with property values. * The returned bean instance may be a wrapper around the original. * <p>The default implementation returns the given {@code bean} as-is. *调用初始化前处理 */ @Nullable default Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException { return bean; } /** * Apply this BeanPostProcessor to the given new bean instance <i>after</i> any bean * initialization callbacks (like InitializingBean's {@code afterPropertiesSet} * or a custom init-method). The bean will already be populated with property values. * The returned bean instance may be a wrapper around the original. * <p>In case of a FactoryBean, this callback will be invoked for both the FactoryBean * instance and the objects created by the FactoryBean (as of Spring 2.0). The * post-processor can decide whether to apply to either the FactoryBean or created * objects or both through corresponding {@code bean instanceof FactoryBean} checks. * <p>This callback will also be invoked after a short-circuiting triggered by a * {@link InstantiationAwareBeanPostProcessor#postProcessBeforeInstantiation} method, * in contrast to all other BeanPostProcessor callbacks. * 调用初始化后处理 */ @Nullable default Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException { return bean; }看简单的实现用例：
public class BeanInitializationDemo implements BeanPostProcessor { @Override public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException { if(bean instanceof UserHolder){ UserHolder userHolder = (UserHolder) bean; System.out.println("初始化前调用 PostProcessorBeforeInitialiation"); userHolder.setDescript("我经历过了postProcessBeforeInitialization"); } return bean; } }注意：beanFactory的例子中只能手动添加BeanPostProcessor。
public class BeanLifyCycleDemo { public static void main(String[] args) { DefaultListableBeanFactory beanFactory = new DefaultListableBeanFactory(); // beanPostProcessor只能手动添加到beanFactory,不像applicationContext可以自己修改beanfactory的BeanPostProcessor beanFactory.addBeanPostProcessor(new BeanInitializationDemo()); XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory); beanDefinitionReader.loadBeanDefinitions("META-INF/dependency-lookup-context.xml"); beanFactory.addBeanPostProcessor(new BeanInstantiaitionAwareImpl()); UserHolder userHolder = (UserHolder)beanFactory.getBean("userHolder"); System.out.println(userHolder); } }看输出：
ApplicationContext的例子
public class BeanLifeCycleInApplicationContextDemo { public static void main(String[] args) { ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext("META-INF/dependency-lookup-context.xml"); applicationContext.refresh(); applicationContext.getBean(UserHolder.class); applicationContext.close(); } }xml：
输出：
