Spring执行ApplicationEvent事件顺序ServletWebServerInitializedEvent
测试代码：
package com.github.abel533.event; import com.github.abel533.C; import org.springframework.context.ApplicationEvent; import org.springframework.context.ApplicationListener; import org.springframework.stereotype.Component; /** * @author liuzh */ @Component public class ApplicationListenerImpl implements ApplicationListener<ApplicationEvent> { public ApplicationListenerImpl() { C.print("ApplicationListenerImpl#constructor"); } @Override public void onApplicationEvent(ApplicationEvent event) { C.print("ApplicationListener#" + event.getClass().getSimpleName()); } }
package com.github.abel533.event; import com.github.abel533.lifecycle.BeanLifecycle; import org.springframework.boot.SpringApplication; import org.springframework.boot.autoconfigure.SpringBootApplication; import org.springframework.context.annotation.Bean; @SpringBootApplication public class ListenerApplication { public static void main(String[] args) { SpringApplication.run(ListenerApplication.class, args).close(); } }
用以上代码实现 ApplicationListener 接口，输出所有事件。
当以 @Component 方式配置时
事件触发顺序如下：
ApplicationListener#ContextRefreshedEvent
ApplicationListener#ServletWebServerInitializedEvent
ApplicationListener#ApplicationStartedEvent
ApplicationListener#ApplicationReadyEvent
ApplicationListener#ContextClosedEvent
当通过 /META-INF/spring.factories 配置时
配置内容如下：
org.springframework.context.ApplicationListener=com.github.abel533.event.ApplicationListenerImpl
此时输出的事件顺序如下：
差异
很容易通过对比发现，Event 触发的时间极早，以至于 @Component 方式只能从第 4 个事件才开始获取到。
从这两种方式的加载时机来看这个差异产生的原因。
在 SpringApplication 构造方法中，就调用 getSpringFactoriesInstances 来获取 /META-INF/spring.factories 配置的 ApplicationListener，代码如下：
public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) { this.resourceLoader = resourceLoader; Assert.notNull(primarySources, "PrimarySources must not be null"); this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources)); this.webApplicationType = WebApplicationType.deduceFromClasspath(); setInitializers((Collection) getSpringFactoriesInstances( ApplicationContextInitializer.class)); setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class)); this.mainApplicationClass = deduceMainApplicationClass(); }
在 SpringFactoriesLoader#loadFactoryNames 实现了从该配置文件获取实现名的方法。从这之后就能收到后续触发的事件。
通过 @Component 方式时，在 SpringApplication#refresh 中调用 registerListeners 获取的所有 ApplicationListener 接口的实现。代码如下：
@Override public void refresh() throws BeansException, IllegalStateException { synchronized (this.startupShutdownMonitor) { try { // 注册所有 ApplicationListener 实现 registerListeners(); // Instantiate all remaining (non-lazy-init) singletons. finishBeanFactoryInitialization(beanFactory); // 这里会触发 ContextRefreshedEvent finishRefresh(); } } }
下面先分析前 4 个无法获取的事件顺序。
ApplicationStartingEvent
第 0 个事件是在 EventPublishingRunListener#starting 中发布的，代码如下：
@Override public void starting() { this.initialMulticaster.multicastEvent( new ApplicationStartingEvent(this.application, this.args)); }
此时的堆栈调用情况如下：
onApplicationEvent:15, ApplicationListenerImpl (com.github.abel533.event) doInvokeListener:172, SimpleApplicationEventMulticaster (org.springframework.context.event) invokeListener:165, SimpleApplicationEventMulticaster (org.springframework.context.event) multicastEvent:139, SimpleApplicationEventMulticaster (org.springframework.context.event) multicastEvent:127, SimpleApplicationEventMulticaster (org.springframework.context.event) starting:69, EventPublishingRunListener (org.springframework.boot.context.event) starting:48, SpringApplicationRunListeners (org.springframework.boot) run:302, SpringApplication (org.springframework.boot) run:1260, SpringApplication (org.springframework.boot) run:1248, SpringApplication (org.springframework.boot) main:12, ListenerApplication (com.github.abel533.event)
ApplicationEnvironmentPreparedEvent
第 1 个事件是在 EventPublishingRunListener#environmentPrepared 中发布的，代码如下：
@Override public void environmentPrepared(ConfigurableEnvironment environment) { this.initialMulticaster.multicastEvent(new ApplicationEnvironmentPreparedEvent( this.application, this.args, environment)); }
此时的堆栈调用情况如下：
onApplicationEvent:15, ApplicationListenerImpl (com.github.abel533.event) doInvokeListener:172, SimpleApplicationEventMulticaster (org.springframework.context.event) invokeListener:165, SimpleApplicationEventMulticaster (org.springframework.context.event) multicastEvent:139, SimpleApplicationEventMulticaster (org.springframework.context.event) multicastEvent:127, SimpleApplicationEventMulticaster (org.springframework.context.event) environmentPrepared:75, EventPublishingRunListener (org.springframework.boot.context.event) environmentPrepared:54, SpringApplicationRunListeners (org.springframework.boot) prepareEnvironment:347, SpringApplication (org.springframework.boot) run:306, SpringApplication (org.springframework.boot) run:1260, SpringApplication (org.springframework.boot) run:1248, SpringApplication (org.springframework.boot) main:12, ListenerApplication (com.github.abel533.event)
ApplicationContextInitializedEvent
第 2 个事件是在 EventPublishingRunListener#contextPrepared 中发布的，代码如下：
@Override public void contextPrepared(ConfigurableApplicationContext context) { this.initialMulticaster.multicastEvent(new ApplicationContextInitializedEvent( this.application, this.args, context)); }
此时的堆栈调用情况如下：
onApplicationEvent:15, ApplicationListenerImpl (com.github.abel533.event) doInvokeListener:172, SimpleApplicationEventMulticaster (org.springframework.context.event) invokeListener:165, SimpleApplicationEventMulticaster (org.springframework.context.event) multicastEvent:139, SimpleApplicationEventMulticaster (org.springframework.context.event) multicastEvent:127, SimpleApplicationEventMulticaster (org.springframework.context.event) contextPrepared:81, EventPublishingRunListener (org.springframework.boot.context.event) contextPrepared:60, SpringApplicationRunListeners (org.springframework.boot) prepareContext:374, SpringApplication (org.springframework.boot) run:314, SpringApplication (org.springframework.boot) run:1260, SpringApplication (org.springframework.boot) run:1248, SpringApplication (org.springframework.boot) main:12, ListenerApplication (com.github.abel533.event)
ApplicationPreparedEvent
第 3 个事件是在 EventPublishingRunListener#contextLoaded 中发布的，代码如下：
@Override public void contextLoaded(ConfigurableApplicationContext context) { for (ApplicationListener<?> listener : this.application.getListeners()) { if (listener instanceof ApplicationContextAware) { ((ApplicationContextAware) listener).setApplicationContext(context); } context.addApplicationListener(listener); } this.initialMulticaster.multicastEvent( new ApplicationPreparedEvent(this.application, this.args, context)); }
此时的堆栈调用情况如下：
onApplicationEvent:15, ApplicationListenerImpl (com.github.abel533.event) doInvokeListener:172, SimpleApplicationEventMulticaster (org.springframework.context.event) invokeListener:165, SimpleApplicationEventMulticaster (org.springframework.context.event) multicastEvent:139, SimpleApplicationEventMulticaster (org.springframework.context.event) multicastEvent:127, SimpleApplicationEventMulticaster (org.springframework.context.event) contextLoaded:93, EventPublishingRunListener (org.springframework.boot.context.event) contextLoaded:66, SpringApplicationRunListeners (org.springframework.boot) prepareContext:393, SpringApplication (org.springframework.boot) run:314, SpringApplication (org.springframework.boot) run:1260, SpringApplication (org.springframework.boot) run:1248, SpringApplication (org.springframework.boot) main:12, ListenerApplication (com.github.abel533.event)
ContextRefreshedEvent
在上面差异中提到 finishRefresh 会触发 ContextRefreshedEvent，代码如下：
@Override protected void finishRefresh() { super.finishRefresh(); WebServer webServer = startWebServer(); if (webServer != null) { publishEvent(new ServletWebServerInitializedEvent(webServer, this)); } }
注意 super.finishRefresh，代码如下(有删减)：
protected void finishRefresh() { // Publish the final event. publishEvent(new ContextRefreshedEvent(this)); }
ServletWebServerInitializedEvent
注意前面 finishRefresh 方法，如果存在 webServer != null，就会发布 ServletWebServerInitializedEvent。
ApplicationStartedEvent
在 SpringApplication#run 方法中，执行完成后，就会调用 listeners.started(context); 方法，在这里面会发布 ApplicationStartedEvent。
ApplicationReadyEvent
和上面 ApplicationStartedEvent 一样，如下代码(有删减)：
// ApplicationStartedEvent listeners.started(context); callRunners(context, applicationArguments); // ApplicationReadyEvent listeners.running(context);
执行完所有 ApplicationRunner 和 CommandLineRunner 接口方法后，就会调用 listeners.running(context)，在这里面就会发布 ApplicationReadyEvent。
在这之后就没有运行期的主要事件了（不考虑 devtools 重启）。在这个事件里，可以请求zookeeper进行服务注册，以便其它服务发现并调用它等相关操作。
ContextClosedEvent
当调用关闭方法的时候，自然就触发了 ContextClosedEvent，调用堆栈如下：
onApplicationEvent:20, ApplicationListenerImpl (com.github.abel533.event) doInvokeListener:172, SimpleApplicationEventMulticaster (org.springframework.context.event) invokeListener:165, SimpleApplicationEventMulticaster (org.springframework.context.event) multicastEvent:139, SimpleApplicationEventMulticaster (org.springframework.context.event) publishEvent:398, AbstractApplicationContext (org.springframework.context.support) publishEvent:355, AbstractApplicationContext (org.springframework.context.support) doClose:994, AbstractApplicationContext (org.springframework.context.support) close:961, AbstractApplicationContext (org.springframework.context.support) main:12, ListenerApplication (com.github.abel533.event)
本文转自：https://blog.csdn.net/isea533/article/details/100146833
