Spring 源码(8)Spring BeanPostProcessor的注册、国际化及事件发布机制
阅读原文时间:2022年05月06日阅读:1

上一篇文章https://www.cnblogs.com/redwinter/p/16198942.html介绍了Spring的注解的解析过程以及Spring Boot自动装配的原理,大概回顾下:Spring 解析注解是通过BeanFactoryPostProcessor的子接口BeanDefinitionRegistryPostProcessor的实现类ConfigurationClassPostProcessor进行实现的,主要解析了@Componenet@ComponentScans@ComponentScan@PropertySources@PropertySource@Import@ImportResource@Bean,并且是按照这个顺序进行解析的,由于Spring是基于注解开发,比如@Configuration@Service@Controller等注解都是在@Component注解之上定义的,因此这些注解也是在这里解析的,然后就是Spring Boot 自动装配,他是通过@Import注解解析ImportSelector接口的selectorImports方法进行BeanDefinition的解析的,并且在这个方法中,Spring 默认扫描META-INF/spring.factories文件,key@AutoEnableConfiguration注解,value为需要注入的类,最终经过过滤去重得到真正需要注入的类的全类名数组,最终通过loadBeanDefinitions注册到Spring容器中。

接下来继续解读AbstractApplicationContext#refresh方法对BeanPostProcessor的注册。

registerBeanPostProcessors 注册BPP

上源码:

protected void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory) {
  PostProcessorRegistrationDelegate.registerBeanPostProcessors(beanFactory, this);
}

public static void registerBeanPostProcessors(
  ConfigurableListableBeanFactory beanFactory, AbstractApplicationContext applicationContext) {
  // 通过类型获取beanNames
  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.
  // 计算beanProcessor的数量
  int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length;
  // 添加一个BeanPostProcessor,所有上面+1了
  beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));

  // Separate between BeanPostProcessors that implement PriorityOrdered,
  // Ordered, and the rest.
  // PriorityOrdered的bpp
  List<BeanPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
  // 内部的bpp
  List<BeanPostProcessor> internalPostProcessors = new ArrayList<>();
  // Ordered的BPP
  List<String> orderedPostProcessorNames = new ArrayList<>();
  // 没有排序的Bpp
  List<String> nonOrderedPostProcessorNames = new ArrayList<>();
  for (String ppName : postProcessorNames) {
    // 匹配是否是PriorityOrdered类型的bpp,是就加入进去
    if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
      BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
      priorityOrderedPostProcessors.add(pp);
      // 判断是否是合并的mbdpp,这个类有点类似于BFPP的子类bdrpp
      if (pp instanceof MergedBeanDefinitionPostProcessor) {
        internalPostProcessors.add(pp);
      }
    }
    // 匹配是否是Ordered的bpp
    else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
      orderedPostProcessorNames.add(ppName);
    }
    else {
      // 没有排序的bpp
      nonOrderedPostProcessorNames.add(ppName);
    }
  }

  // First, register the BeanPostProcessors that implement PriorityOrdered.
  // 排序
  sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
  // 注册bpp
  registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);

  // Next, register the BeanPostProcessors that implement Ordered.
  // 将beanName转换为BPP对象存放在list中
  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);
    }
  }
  // 排序
  sortPostProcessors(orderedPostProcessors, beanFactory);
  // 注册到容器中
  registerBeanPostProcessors(beanFactory, orderedPostProcessors);

  // Now, register all regular BeanPostProcessors.
  // 处理没有排序的bpp
  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);
    }
  }
  // 注册到容器
  registerBeanPostProcessors(beanFactory, nonOrderedPostProcessors);

  // Finally, re-register all internal BeanPostProcessors.
  // 对内部的bpp进行排序
  sortPostProcessors(internalPostProcessors, beanFactory);
  // 注册内部的bpp
  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).
  // 重新注册ApplicationListenerDetector 的bpp,把它放在了链表的尾部
  // 因为在准备BeanFactory时已经添加过这个bpp
  beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(applicationContext));
}

前面的文章:https://www.cnblogs.com/redwinter/p/16196359.html BeanFactoryPostProcessor的执行和解析的话,这里就很相似了,基本套路都是一样的。

  • 通过getBeanNamesByType 获取BPP的数组
  • 设置集合存储BPP
  • 解析PriorityOrderedBPP,排序,注册,中间加入解析内部的BPP
  • 解析OrderdBPP,排序,注册
  • 解析没有排序的,注册,,中间加入解析内部的BPP
  • 最后注册内部的BPP
  • ApplicationListenerDetector 注册到容器的后面,这个类是之前添加过的(这里:prepareBeanFactory),这里移到了最后

注册BPP都是调用的这个方法遍历处理的:

private static void registerBeanPostProcessors(
  ConfigurableListableBeanFactory beanFactory, List<BeanPostProcessor> postProcessors) {
  for (BeanPostProcessor postProcessor : postProcessors) {
    // 加入到容器中
    beanFactory.addBeanPostProcessor(postProcessor);
  }
}

BFPP 不同的是,BPP只是进行了注册并没有进行执行,BFPP是注册并执行。

BeanPostProcessor 基本上就做了这些事,相对比较简单,接下来解读下AbstractApplicationContext#refresh中对国际化、事件多播器、事件监听器的处理。

初始化国际化

在单纯的Spring中设置国际化实际上是体现不出来的,需要用到Spring MVC 才能有所体现,我们看看Spring是怎么初始化的,上源码:

protected void initMessageSource() {
  // 获取beanFactory
  ConfigurableListableBeanFactory beanFactory = getBeanFactory();
  // 如果工厂中已经有这个bean,那就获取出来设置到messageSource上
  if (beanFactory.containsLocalBean(MESSAGE_SOURCE_BEAN_NAME)) {
    this.messageSource = beanFactory.getBean(MESSAGE_SOURCE_BEAN_NAME, MessageSource.class);
    // Make MessageSource aware of parent MessageSource.
    // 判断父类是否存在,如果存在则将判断父类是否设置了消息源,没有设置就设置给他
    if (this.parent != null && this.messageSource instanceof HierarchicalMessageSource) {
      HierarchicalMessageSource hms = (HierarchicalMessageSource) this.messageSource;
      if (hms.getParentMessageSource() == null) {
        // Only set parent context as parent MessageSource if no parent MessageSource
        // registered already.
        hms.setParentMessageSource(getInternalParentMessageSource());
      }
    }
    if (logger.isTraceEnabled()) {
      logger.trace("Using MessageSource [" + this.messageSource + "]");
    }
  }
  else {
    // Use empty MessageSource to be able to accept getMessage calls.
    // 如果容器中没有注册bean,那么new一个
    DelegatingMessageSource dms = new DelegatingMessageSource();
    dms.setParentMessageSource(getInternalParentMessageSource());
    this.messageSource = dms;
    // 注册到容器中
    beanFactory.registerSingleton(MESSAGE_SOURCE_BEAN_NAME, this.messageSource);
    if (logger.isTraceEnabled()) {
      logger.trace("No '" + MESSAGE_SOURCE_BEAN_NAME + "' bean, using [" + this.messageSource + "]");
    }
  }
}

逻辑很简单,首先是从容器中获取MessageSource接口的实现,如果存在则直接赋值给AbstractApplicationContextmessageSource属性,用于解析国际化和参数化。如果没有就直接new一个委派的实现类,然后赋值给messageSource属性,并注册到容器中。

在Spring中提供了两个默认的实现:ResourceBundleMessageSourceReloadableResourceBundleMessageSource

初始化多播器、刷新容器、注册监听器

initApplicationEventMulticaster初始化多播器,上源码:

protected void initApplicationEventMulticaster() {
  // 获取beanFactory
  ConfigurableListableBeanFactory beanFactory = getBeanFactory();
  // 从容器中获取bean,如果就拿出来
  if (beanFactory.containsLocalBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME)) {
    this.applicationEventMulticaster =
      beanFactory.getBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, ApplicationEventMulticaster.class);
    if (logger.isTraceEnabled()) {
      logger.trace("Using ApplicationEventMulticaster [" + this.applicationEventMulticaster + "]");
    }
  }
  else {
    // 没有事件多播器就new一个,多播器会创建一个监听器的集合,用于存放监听器
    this.applicationEventMulticaster = new SimpleApplicationEventMulticaster(beanFactory);
    // 注册到容器中
    beanFactory.registerSingleton(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, this.applicationEventMulticaster);
    if (logger.isTraceEnabled()) {
      logger.trace("No '" + APPLICATION_EVENT_MULTICASTER_BEAN_NAME + "' bean, using " +
                   "[" + this.applicationEventMulticaster.getClass().getSimpleName() + "]");
    }
  }
}

源码跟国际化的代码基本逻辑一直,如果容器中有就拿出来赋值,没有就创建一个SimpleApplicationEventMulticaster类作为默认的多播器。

onRefresh刷新蓉器这个方法是一个空方法,由子类实现,这里直接跳过了。

registerListeners注册监听器,上源码:

protected void registerListeners() {
        // Register statically specified listeners first.
        // 注册静态指定的监听器
        for (ApplicationListener<?> listener : getApplicationListeners()) {
            getApplicationEventMulticaster().addApplicationListener(listener);
        }

        // Do not initialize FactoryBeans here: We need to leave all regular beans
        // uninitialized to let post-processors apply to them!
        // 根据类型获取监听器的beanName
        String[] listenerBeanNames = getBeanNamesForType(ApplicationListener.class, true, false);
        // 遍历bean,并加入到监听器bean集合中
        for (String listenerBeanName : listenerBeanNames) {
            getApplicationEventMulticaster().addApplicationListenerBean(listenerBeanName);
        }

        // Publish early application events now that we finally have a multicaster...
        // 获取早期的事件,这个事件是在准备刷新阶段(第一个阶段前戏阶段)设置进来的,是一个空的集合
        Set<ApplicationEvent> earlyEventsToProcess = this.earlyApplicationEvents;
        this.earlyApplicationEvents = null;
        if (!CollectionUtils.isEmpty(earlyEventsToProcess)) {
            for (ApplicationEvent earlyEvent : earlyEventsToProcess) {
                getApplicationEventMulticaster().multicastEvent(earlyEvent);
            }
        }
    }

这里的逻辑也是比较简单的:

  • 先获取静态的监听器,这里实际上就是在定制化BeanFactory时可以手动添加的监听器,如果有就添加到多播器的监听器集合中

    @Override
        protected void customizeBeanFactory(DefaultListableBeanFactory beanFactory) {
            // 扩展点 设置不去处理循环依赖或者beanDefinition覆盖
            super.setAllowBeanDefinitionOverriding(true);
            super.setAllowCircularReferences(true);
            super.customizeBeanFactory(beanFactory);
            // 添加一个自定义的属性编辑器的注册器
            beanFactory.addPropertyEditorRegistrar(new AddressPropertyEditorRegistrar());
            super.addBeanFactoryPostProcessor(new MyBeanDefinitionRegistryPostProcessor("new 创建的"));
            // 添加一个自定义的BeanPostProcessorr
            // beanFactory.addBeanPostProcessor(null);
            // 添加一个监听器
            super.addApplicationListener(new CustomApplicationListener());
        }
  • 获取定义为Bean的ApplicationListener,比如xml配置的,如果有就添加到多播器的监听器集合中

  • 获取早期的事件,这里获取到的是一个空集合

Spring的事件发布是如何设计的?

Spring的事件机制实际上是使用了观察者模式进行设计的,观察者模式分为两大角色,观察者和被观察者,只是Spring更加的抽象,在Spring中分为事件ApplicationEvent、监听器ApplicationListener、事件发布者ApplicationEventPublisher、事件的多播器ApplicationEventMulticasterAbstractApplicationContext这个SpringBeanFactory容器就是实现了ApplicationEventPublisher,可以对事件进行发布。在Spring中内置了很多的事件,比如:ContextClosedEventContextRefreshedEventContextStartedEventContextStopedEvent,而监听器的话Spring内置不多,Spring还提供了注解方式的配置监听器,注解为@EventListener

观察者模式与Spring事件驱动的对比:

在Spring 中如何使用事件,我们可以直接到官网 https://docs.spring.io/spring-framework/docs/current/reference/html/core.html#context-functionality-events 可以找到事件的使用案例,

想了解的朋友可以直接点击链接去查看,官网提供了两种配置监听器的方式,一种是实现ApplicationListener接口,一种是使用@EventLister注解配置,基于注解还可以配置异步的,排序的。

在自定义的事件发布时需要实现ApplicationEventPublisherAware 接口获取到ApplicationEventPublisher 进行发布事件。

上代码:

代码是Spring官网提供的,功能就是如果邮箱被拉黑,那么就不发送消息给邮箱,而是发布一个事件进行其他处理

定义一个事件源发布者:用来处理黑名单的邮箱

/**
 * @author <a href="https://www.cnblogs.com/redwinter/">redwinter</a>
 * @since 1.0
 **/
public class EmailService implements ApplicationEventPublisherAware {

  private List<String> blackList;

  public List<String> getBlackList() {
    return blackList;
  }

  public void setBlackList(List<String> blackList) {
    this.blackList = blackList;
  }

  private ApplicationEventPublisher applicationEventPublisher;

  @Override
  public void setApplicationEventPublisher(ApplicationEventPublisher applicationEventPublisher) {
    this.applicationEventPublisher = applicationEventPublisher;
  }

  public void sendEmail(String address,String context){
    if (blackList.contains(address)){
      // 在黑名单中,那么发布一个事件,但是不发送消息到邮箱
      applicationEventPublisher.publishEvent(new MyEvent(this,address,context));
      return;
    }
    System.out.println("......发送邮箱........");
  }
}

定义事件

/**
 * @author <a href="https://www.cnblogs.com/redwinter/">redwinter</a>
 * @since 1.0
 **/
public class MyEvent extends ApplicationEvent {

    private final String address;
    private final String context;

    /**
     * Create a new {@code ApplicationEvent}.
     *
     * @param source the object on which the event initially occurred or with
     *               which the event is associated (never {@code null})
     */
    public MyEvent(Object source,String address,String context) {
        super(source);
        this.address = address;
        this.context = context;
    }

    @Override
    public String toString() {
        return "MyEvent{" +
                "address='" + address + '\'' +
                ", context='" + context + '\'' +
                '}';
    }
}

定义监听器:

/**
 * @author <a href="https://www.cnblogs.com/redwinter/">redwinter</a>
 * @since 1.0
 **/
public class MyApplicationListener implements ApplicationListener<MyEvent> {

    private String notifyAddress;

    public String getNotifyAddress() {
        return notifyAddress;
    }

    public void setNotifyAddress(String notifyAddress) {
        this.notifyAddress = notifyAddress;
    }

    @Override
    public void onApplicationEvent(MyEvent event) {
        System.out.println("收到事件,开始发布");
        System.out.println("发送消息给" + notifyAddress + event.toString());
    }
}

配置xml:

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:mvc="http://www.springframework.org/schema/mvc"
       xmlns:context="http://www.springframework.org/schema/context"
       xmlns:redwinter="http://www.redwinter.com/schema/redwinter"
       xsi:schemaLocation="http://www.springframework.org/schema/mvc https://www.springframework.org/schema/mvc/spring-mvc-3.1.xsd
        http://www.springframework.org/schema/beans https://www.springframework.org/schema/beans/spring-beans-3.1.xsd
        http://www.springframework.org/schema/context https://www.springframework.org/schema/context/spring-context.xsd
        http://www.redwinter.com/schema/redwinter  http://www.redwinter.com/schema/redwinter.xsd
        ">
<!--配置事件监听-->
    <bean class="com.redwinter.test.EmailService">
        <property name="blackList">
            <list>
                <value>12345@qq.com</value>
                <value>123@qq.com</value>
                <value>456@qq.com</value>
            </list>
        </property>
    </bean>
    <bean class="com.redwinter.test.MyApplicationListener">
        <property name="notifyAddress" value="789@qq.com"/>
    </bean>

</beans>

客户端:

ClassPathXmlApplicationContext context = new MyClassPathXmlApplicationContext("classpath:spring-test.xml");
EmailService emailService = context.getBean(EmailService.class);
emailService.sendEmail("123@qq.com","Spring源码学习中!");

我这里发送的邮箱在拉黑的配置文件中,所以就会触发事件的发布并且将拉黑的邮箱信息发送给789@qq.com这个通知邮箱,如果设置成其他的邮箱,那么就能正常进行发送消息。

输出:

收到事件,开始发布
发送消息给789@.comMyEvent{address='123@qq.com', context='你好啊,Spring源码!'}

当然可有使用注解@EventListener进行配置:

/**
 * @author <a href="https://www.cnblogs.com/redwinter/">redwinter</a>
 * @since 1.0
 **/
public class MyNotifier {

    private String notifyAddress;

    public String getNotifyAddress() {
        return notifyAddress;
    }

    public void setNotifyAddress(String notifyAddress) {
        this.notifyAddress = notifyAddress;
    }

    @EventListener
    public void processMessage(MyEvent event){
        System.out.println("收到事件,开始发布");
        System.out.println("发送消息给" + notifyAddress + event.toString());
    }
}

xml增加一项配置:开启扫描和新增一个Bean的配置

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:mvc="http://www.springframework.org/schema/mvc"
       xmlns:context="http://www.springframework.org/schema/context"
       xmlns:redwinter="http://www.redwinter.com/schema/redwinter"
       xsi:schemaLocation="http://www.springframework.org/schema/mvc https://www.springframework.org/schema/mvc/spring-mvc-3.1.xsd
        http://www.springframework.org/schema/beans https://www.springframework.org/schema/beans/spring-beans-3.1.xsd
        http://www.springframework.org/schema/context https://www.springframework.org/schema/context/spring-context.xsd
        http://www.redwinter.com/schema/redwinter  http://www.redwinter.com/schema/redwinter.xsd
        ">
  <context:component-scan base-package="com.redwinter.test"/>
<!--配置事件监听-->
    <bean class="com.redwinter.test.selfevent.EmailService">
        <property name="blackList">
            <list>
                <value>12345@qq.com</value>
                <value>123@qq.com</value>
                <value>456@qq.com</value>
            </list>
        </property>
    </bean>
    <bean class="com.redwinter.test.selfevent.MyApplicationListener">
        <property name="notifyAddress" value="789@.com"/>
    </bean>
    <bean class="com.redwinter.test.selfevent.MyNotifier">
        <property name="notifyAddress" value="7888@.com"/>
    </bean>
  </beans>

输出:

收到事件,开始发布
发送消息给7888@.comMyEvent{address='123@qq.com', context='你好啊,Spring源码!'}
收到事件,开始发布
发送消息给789@.comMyEvent{address='123@qq.com', context='你好啊,Spring源码!'}

说明生效了,那么@EventListenter是如何解析的呢?

@EventListener注解如何解析的?

实际上在分析BFPP https://www.cnblogs.com/redwinter/p/16198942.html的时候,我们分析了Spring对注解的解析,提到了如果开启了Spring的注解扫描,那么Spring默认会在容器中添加几个内置的Bean,并且以internal开头的Bean对象,这些Bean都是在AnnotationConfigUtils这个类中设置的:

//... 省略代码....
// 创建一个 EventListenerMethodProcessor 的BeanDefinition
if (!registry.containsBeanDefinition(EVENT_LISTENER_PROCESSOR_BEAN_NAME)) {
  RootBeanDefinition def = new RootBeanDefinition(EventListenerMethodProcessor.class);
  def.setSource(source);
  beanDefs.add(registerPostProcessor(registry, def, EVENT_LISTENER_PROCESSOR_BEAN_NAME));
}
// 创建一个 DefaultEventListenerFactory 的BeanDefinition
if (!registry.containsBeanDefinition(EVENT_LISTENER_FACTORY_BEAN_NAME)) {
  RootBeanDefinition def = new RootBeanDefinition(DefaultEventListenerFactory.class);
  def.setSource(source);
  beanDefs.add(registerPostProcessor(registry, def, EVENT_LISTENER_FACTORY_BEAN_NAME));
}
//... 省略代码....

可以看到设置了一个EventListenerMethodProcessor类还有一个DefaultEventListenerFactory,这两个类分别用来解析@EvenListener和创建ApplicationListener接口的适配器。

EventListenerMethodProcessor 实现了BeanFactoryPostProcessor接口、SmartInitializingSingleton接口和ApplicationContextAware接口,BeanFactoryPostProcessor接口是用来对BeanDefinition进行个性化设置解析等操作,SmartInitializingSingleton接口是在初始化所有的单例Bean之后触发的,也就是在preInstantiateSingletons方法中初始化Bean之后调用,ApplicationContextAware是用来获取ApplicationContext的。

截取EventListenerMethodProcessor类中的的部分代码:

// ... 省略代码....
// 遍历所有标有@EventListener注解的方法
for (Method method : annotatedMethods.keySet()) {
  for (EventListenerFactory factory : factories) {
    if (factory.supportsMethod(method)) {
      Method methodToUse = AopUtils.selectInvocableMethod(method, context.getType(beanName));
      // 使用工厂创建一个监听器,实际上创建的就是一个ApplicationListenerMethodAdapter
      ApplicationListener<?> applicationListener =
        factory.createApplicationListener(beanName, targetType, methodToUse);
      if (applicationListener instanceof ApplicationListenerMethodAdapter) {
        ((ApplicationListenerMethodAdapter) applicationListener).init(context, this.evaluator);
      }
      // 添加到容器中,如果多播器不为空,则添加到多播器的监听器集合中
      context.addApplicationListener(applicationListener);
      break;
    }
  }
}
// ... 省略代码....

public ApplicationListener<?> createApplicationListener(String beanName, Class<?> type, Method method) {
  return new ApplicationListenerMethodAdapter(beanName, type, method);
}

到这里SpringAbstractApplicationContext#refresh方法中的10多个方法已经分析了10个了,接下来分析Bean的创建过程,应该是Spring源码中最重要的过程了。