ApplicationListener類初始化位置

在類SpringApplication的構造方法，第267行

在META-INFO/spring.factories中配置的實現類
spring-boot

# Application Listeners
org.springframework.context.ApplicationListener=\
org.springframework.boot.ClearCachesApplicationListener,\
org.springframework.boot.builder.ParentContextCloserApplicationListener,\
org.springframework.boot.context.FileEncodingApplicationListener,\
org.springframework.boot.context.config.AnsiOutputApplicationListener,\
org.springframework.boot.context.config.DelegatingApplicationListener,\
org.springframework.boot.context.logging.LoggingApplicationListener,\
org.springframework.boot.env.EnvironmentPostProcessorApplicationListener

spring-boot-autoconfigure

# Application Listeners
org.springframework.context.ApplicationListener=\
org.springframework.boot.autoconfigure.BackgroundPreinitializer

相關類

• ApplicationEvent 事件祖先類
• org.springframework.context.event.ApplicationEventMulticaster 事件多播器
• org.springframework.context.event.SmartApplicationListener 監聽器
• org.springframework.context.event.GenericApplicationListener 監聽器
• org.springframework.context.event.EventListener 監聽器

SpringBoot啟動過程中的事件，都由org.springframework.context.event.ApplicationEventMulticaster播出去，讓監聽器處理。

監聽器觸發邏輯

從加載開始

入口在SpringApplication的構造方法，第267行
類工廠加載ApplicationListener的實現類

setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));

然后在SpringApplication的實例方法run中，第297行，加載SpringApplicationRunListeners類，這個類中持有多播器的引用。

SpringApplicationRunListeners listeners = getRunListeners(args);

SpringApplicationRunListeners實例化的時候，會通過工廠類加載SpringApplicationRunListener

private SpringApplicationRunListeners getRunListeners(String[] args) {Class<?>[] types = new Class<?>[] { SpringApplication.class, String[].class };return new SpringApplicationRunListeners(logger,getSpringFactoriesInstances(SpringApplicationRunListener.class, types, this, args),this.applicationStartup);
}

SpringApplicationRunListener的實現類

# Run Listeners
org.springframework.boot.SpringApplicationRunListener=\
org.springframework.boot.context.event.EventPublishingRunListener

EventPublishingRunListener中持有的監聽器，就是SpringApplication中加載的ApplicationListener的實現類

public EventPublishingRunListener(SpringApplication application, String[] args) {this.application = application;this.args = args;this.initialMulticaster = new SimpleApplicationEventMulticaster();for (ApplicationListener<?> listener : application.getListeners()) {this.initialMulticaster.addApplicationListener(listener);}
}

• ClearCachesApplicationListener
• ParentContextCloserApplicationListener
• FileEncodingApplicationListener
• AnsiOutputApplicationListener
• DelegatingApplicationListener
• LoggingApplicationListener
• EnvironmentPostProcessorApplicationListener
• BackgroundPreinitializer

存儲

然后這些監聽器被放入了SimpleApplicationEventMulticaster簡單多播器里面

@Override
public void addApplicationListener(ApplicationListener<?> listener) {synchronized (this.defaultRetriever) {// Explicitly remove target for a proxy, if registered already,// in order to avoid double invocations of the same listener.Object singletonTarget = AopProxyUtils.getSingletonTarget(listener);if (singletonTarget instanceof ApplicationListener) {this.defaultRetriever.applicationListeners.remove(singletonTarget);}this.defaultRetriever.applicationListeners.add(listener);this.retrieverCache.clear();}
}

默認的defaultRetriever則是一個內部類DefaultListenerRetriever

觸發

會在多個地方觸發，比如
SpringApplication的run方法，第298行

listeners.starting(bootstrapContext, this.mainApplicationClass);

觸發過程又涉及到事件的設計