Spring 执行顺序：Event 事件

我就是我 2024-04-17 18:30 100阅读 0赞

[**回目录**][Link 1]

> 代码：[https://gitee.com/free/boot-order/tree/master/src/main/java/com/github/abel533/event][https_gitee.com_free_boot-order_tree_master_src_main_java_com_github_abel533_event]

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：

1.  `ApplicationListener#ContextRefreshedEvent`
2.  `ApplicationListener#ServletWebServerInitializedEvent`
3.  `ApplicationListener#ApplicationStartedEvent`
4.  `ApplicationListener#ApplicationReadyEvent`
5.  `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：

1.  `ApplicationListener#ApplicationStartingEvent`
2.  `ApplicationListener#ApplicationEnvironmentPreparedEvent`
    
        .   ____          _            __ _ _
         /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
        ( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
         \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
          '  |____| .__|_| |_|_| |_\__, | / / / /
         =========|_|==============|___/=/_/_/_/
         :: Spring Boot ::        (v2.1.1.RELEASE)
3.  `ApplicationListener#ApplicationContextInitializedEvent`
4.  `ApplicationListener#ApplicationPreparedEvent`
5.  `ApplicationListener#ContextRefreshedEvent` **这里**
6.  `ApplicationListener#ServletWebServerInitializedEvent`
7.  `ApplicationListener#ApplicationStartedEvent`
8.  `ApplicationListener#ApplicationReadyEvent`
9.  `ApplicationListener#ContextClosedEvent`

### 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）。

### 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)

[Link 1]: https://liuzh.blog.csdn.net/article/details/100146590
[https_gitee.com_free_boot-order_tree_master_src_main_java_com_github_abel533_event]: https://gitee.com/free/boot-order/tree/master/src/main/java/com/github/abel533/event