springapplication之SpringApplicationRunListeners

上文讲述了SpringApplication启动的基本流程，下文展开将run方法

SpringApplicationRunListeners listeners = getRunListeners(args);
//这里从spring.factories文件中读取配置
//读到的类有org.springframework.boot.context.event.EventPublishingRunListener
private SpringApplicationRunListeners getRunListeners(String[] args) {
Class<?>[] types = new Class<?>[] { SpringApplication.class, String[].class };
return new SpringApplicationRunListeners(logger,
getSpringFactoriesInstances(SpringApplicationRunListener.class, types, this, args));
}
//EventPublishingRunListener，SpringApplication构造器加载的一些listener都会加入该类
//
public EventPublishingRunListener(SpringApplication application, String[] args) {
this.application = application;
this.args = args;
//声明代理类initialMulticaster，所有事件都由它处理
this.initialMulticaster = new SimpleApplicationEventMulticaster();
for (ApplicationListener<?> listener : application.getListeners()) {
this.initialMulticaster.addApplicationListener(listener);
}
}
/*
//EventPublishingRunListener的SimpleApplicationEventMulticaster.multicastEvent
starting
environmentPrepared
contextPrepared
contextLoaded
//发布事件给context
started
running
//如果context存活发布事件给context，否则给initialMulticaster私有
failed
*/
@Override
public void multicastEvent(ApplicationEvent event) {
multicastEvent(event, resolveDefaultEventType(event));
}
//发布事件并寻找合适的监听者来执行监听的事件
@Override
public void multicastEvent(final ApplicationEvent event, @Nullable ResolvableType eventType) {
ResolvableType type = (eventType != null ? eventType : resolveDefaultEventType(event));
Executor executor = getTaskExecutor();
for (ApplicationListener<?> listener : getApplicationListeners(event, type)) {
if (executor != null) {
executor.execute(() -> invokeListener(listener, event));
}
else {
invokeListener(listener, event);
}
}
}
//获取合适的监听器，流程大概是先从缓存找，找不到然后去defaultRetriever里找
protected Collection<ApplicationListener<?>> getApplicationListeners(
ApplicationEvent event, ResolvableType eventType) {
Object source = event.getSource();
Class<?> sourceType = (source != null ? source.getClass() : null);
ListenerCacheKey cacheKey = new ListenerCacheKey(eventType, sourceType);
// Quick check for existing entry on ConcurrentHashMap...
ListenerRetriever retriever = this.retrieverCache.get(cacheKey);
if (retriever != null) {
return retriever.getApplicationListeners();
}
if (this.beanClassLoader == null ||
(ClassUtils.isCacheSafe(event.getClass(), this.beanClassLoader) &&
(sourceType == null || ClassUtils.isCacheSafe(sourceType, this.beanClassLoader)))) {
// Fully synchronized building and caching of a ListenerRetriever
synchronized (this.retrievalMutex) {
retriever = this.retrieverCache.get(cacheKey);
if (retriever != null) {
return retriever.getApplicationListeners();
}
retriever = new ListenerRetriever(true);
//关注这里
Collection<ApplicationListener<?>> listeners =
retrieveApplicationListeners(eventType, sourceType, retriever);
this.retrieverCache.put(cacheKey, retriever);
return listeners;
}
}
else {
// No ListenerRetriever caching -> no synchronization necessary
return retrieveApplicationListeners(eventType, sourceType, null);
}
}
private Collection<ApplicationListener<?>> retrieveApplicationListeners(
ResolvableType eventType, @Nullable Class<?> sourceType, @Nullable ListenerRetriever retriever) {
List<ApplicationListener<?>> allListeners = new ArrayList<>();
Set<ApplicationListener<?>> listeners;
Set<String> listenerBeans;
synchronized (this.retrievalMutex) {
listeners = new LinkedHashSet<>(this.defaultRetriever.applicationListeners);
listenerBeans = new LinkedHashSet<>(this.defaultRetriever.applicationListenerBeans);
}
for (ApplicationListener<?> listener : listeners) {
if (supportsEvent(listener, eventType, sourceType)) {
if (retriever != null) {
//添加缓存
retriever.applicationListeners.add(listener);
}
allListeners.add(listener);
}
}
//对于applicationcontext而言，abstractApplicationContext refresh模版方法会调用 registerListeners();

//然后调用 applicationListenerBeans 该方法会注册listener，
//然后添加到 applicationListenerBeans（存放用户自定义listener）中，当所以每次找到listener的时候会尝试
//初始化applicationListenerBeans的bean
if (!listenerBeans.isEmpty()) {
BeanFactory beanFactory = getBeanFactory();
for (String listenerBeanName : listenerBeans) {
try {
Class<?> listenerType = beanFactory.getType(listenerBeanName);
if (listenerType == null || supportsEvent(listenerType, eventType)) {
ApplicationListener<?> listener =
beanFactory.getBean(listenerBeanName, ApplicationListener.class);
if (!allListeners.contains(listener) && supportsEvent(listener, eventType, sourceType)) {
if (retriever != null) {
if (beanFactory.isSingleton(listenerBeanName)) {
retriever.applicationListeners.add(listener);
}
else {
retriever.applicationListenerBeans.add(listenerBeanName);
}
}
allListeners.add(listener);
}
}
}
catch (NoSuchBeanDefinitionException ex) {
// Singleton listener instance (without backing bean definition) disappeared -
// probably in the middle of the destruction phase
}
}
}
AnnotationAwareOrderComparator.sort(allListeners);
if (retriever != null && retriever.applicationListenerBeans.isEmpty()) {
retriever.applicationListeners.clear();
retriever.applicationListeners.addAll(allListeners);
}
return allListeners;
}

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