V2AS问路
spring-boot-learning-监听事件
阅读原文时间：2023年07月09日阅读：1

Springboot扩展了Spring的ApplicatoionContextEvent，提供了事件：

ApplicationStartingEvent:框架启动事件

ApplicationEnvironmentPreparedEvent: springboot 对应Evironment已经准备完毕了，但是上下文还没有创建。

ApplicationContextInitializedEvent:  上下文初始化

ApplicationPreparedEvent:    springboot 上下文context创建完成，但是bean没有完全加载

ApplicationStartedEvent:   springboot 启动开始执行的事件

ApplicationReadyEvent :   调用Runners接口完毕

ApplicationFailedEvent：启动异常执行事件

* springboot自带的事件。
* ApplicationStartingEvent
* Spring Application启动事件。事件产生的时机为ApplicationListeners注册之后，Environment或ApplicationContext可用之前，
　　　　事件源为Spring Application自身，ApplicationStartingEvent在生命周期过程中可能会被修改，请谨慎使用。

* ApplicationEnvironmentPreparedEvent
* 事件产生的时机为Spring Application已经启动，Environment第一次可用。

* ApplicationPreparedEvent
* 事件产生的时机为Spring Application已经启动，Application Context已经完全准备好但是还没有进行刷新，在该阶段已经开始加载Bean定义并且Environment已经完全可用。

* ApplicationStartedEvent
* 事件产生的时机为Application Context已经完成刷新，ApplicationRunner application和CommandLineRunner调用之前。

* ApplicationReadyEvent
* Spring Application已经准备好对外提供服务。

* ApplicationFailedEvent
* 应用启动失败

自定义监听器的步骤：

1，建立监听类继承ApplicationListener

2, 继承方法onApplicationEvent

3, 在resource建立文件夹/META-INF/spring.factories

4, 文件里写入：

org.springframework.context.ApplicationListener=\
com.quan.sbrabbit.Listener.QuanListenerEnvPreparedEvent ,com.quan.sbrabbit.Listener.QuanListenerStartedEvent,com.quan.sbrabbit.Listener.QuanListenerPreparedEvent

/**
* spring boot 对应Enviroment已经准备完毕，但此时上下文context还没有创建。在该监听中获取到ConfigurableEnvironment
* 后可以对配置信息做操作，例如：修改默认的配置信息
*/

public class QuanListenerEnvPreparedEvent implements ApplicationListener {
@Override
public void onApplicationEvent(ApplicationEnvironmentPreparedEvent event) {
ConfigurableEnvironment environment = event.getEnvironment();
MutablePropertySources sources =environment.getPropertySources();
if (sources != null){
Iterator> iterator = sources.iterator();
while (iterator.hasNext()){
PropertySource propertySource = iterator.next();
System.out.println(propertySource.getName());
System.out.println(propertySource.getSource());
System.out.println(propertySource.getClass());
}
System.out.println("监听到ApplicationEnvironmentPreparedEvent");
// for (PropertySource p :
// sources) {
// System.out.println(p.getName());
// System.out.println(p.getSource());
// System.out.println(p.getClass());
// }
}
}
}

/**
* pring boot上下文context创建完成，但此时spring中的bean是没有完全加载完成的。
* 在获取完上下文后，可以将上下文传递出去做一些额外的操作。
* 值得注意的是：在该监听器中是无法获取自定义bean并进行操作的。
*/
public class QuanListenerPreparedEvent implements ApplicationListener {
@Override
public void onApplicationEvent(ApplicationPreparedEvent event) {
ConfigurableApplicationContext context = event.getApplicationContext();
context.toString();
System.out.println("监听到ApplicationPreparedEvent");
}
}

public class QuanListenerStartedEvent implements ApplicationListener {
@Override
public void onApplicationEvent(ApplicationStartedEvent event) {
SpringApplication application = event.getSpringApplication();
System.out.println(application);
//控制台或日志中会默认显示一个Banner,关闭这个东西
application.setBannerMode(Banner.Mode.OFF);
System.out.println("监听到applicationStartedEvent");
}
}

加入：

org.springframework.context.ApplicationListener=\
com.quan.sbrabbit.Listener.QuanListenerEnvPreparedEvent ,com.quan.sbrabbit.Listener.QuanListenerStartedEvent,com.quan.sbrabbit.Listener.QuanListenerPreparedEvent

运行输出：

监听到ApplicationEnvironmentPreparedEvent

. ____ _ __ _ _
/\\ / ___'_ __ _ _(_)_ __ __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
\\/ ___)| |_)| | | | | || (_| | ) ) ) )
' |____| .__|_| |_|_| |_\__, | / / / /
=========|_|==============|___/=/_/_/_/
:: Spring Boot :: (v2.3.3.RELEASE)

2020-09-01 14:10:32.063 WARN 99192 --- [ main] o.s.boot.StartupInfoLogger : InetAddress.getLocalHost().getHostName() took 5004 milliseconds to respond. Please verify your network configuration (macOS machines may need to add entries to /etc/hosts).
2020-09-01 14:10:37.067 INFO 99192 --- [ main] com.quan.sbrabbit.SbrabbitApplication : Starting SbrabbitApplication on quandeMacBook-Pro.local with PID 99192 (/Users/quan/Desktop/ALLLL/sbrabbit/target/classes started by quan in /Users/quan/Desktop/ALLLL/sbrabbit)
2020-09-01 14:10:37.068 INFO 99192 --- [ main] com.quan.sbrabbit.SbrabbitApplication : No active profile set, falling back to default profiles: default
监听到ApplicationPreparedEvent
2020-09-01 14:10:37.491 INFO 99192 --- [ main] .s.d.r.c.RepositoryConfigurationDelegate : Bootstrapping Spring Data Elasticsearch repositories in DEFAULT mode.
2020-09-01 14:10:37.505 INFO 99192 --- [ main] .s.d.r.c.RepositoryConfigurationDelegate : Finished Spring Data repository scanning in 11ms. Found 0 Elasticsearch repository interfaces.
2020-09-01 14:10:37.509 INFO 99192 --- [ main] .s.d.r.c.RepositoryConfigurationDelegate : Bootstrapping Spring Data Reactive Elasticsearch repositories in DEFAULT mode.
2020-09-01 14:10:37.511 INFO 99192 --- [ main] .s.d.r.c.RepositoryConfigurationDelegate : Finished Spring Data repository scanning in 2ms. Found 0 Reactive Elasticsearch repository interfaces.
2020-09-01 14:10:37.762 INFO 99192 --- [ main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat initialized with port(s): 9898 (http)
2020-09-01 14:10:37.768 INFO 99192 --- [ main] o.apache.catalina.core.StandardService : Starting service [Tomcat]
2020-09-01 14:10:37.769 INFO 99192 --- [ main] org.apache.catalina.core.StandardEngine : Starting Servlet engine: [Apache Tomcat/9.0.37]
2020-09-01 14:10:37.838 INFO 99192 --- [ main] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring embedded WebApplicationContext
2020-09-01 14:10:37.839 INFO 99192 --- [ main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 740 ms
2020-09-01 14:10:38.006 INFO 99192 --- [ main] o.s.s.concurrent.ThreadPoolTaskExecutor : Initializing ExecutorService 'applicationTaskExecutor'
2020-09-01 14:10:38.502 WARN 99192 --- [ main] o.s.data.convert.CustomConversions : Registering converter from class org.springframework.data.geo.Point to interface java.util.Map as writing converter although it doesn't convert to a store-supported type! You might want to check your annotation setup at the converter implementation.
2020-09-01 14:10:38.502 WARN 99192 --- [ main] o.s.data.convert.CustomConversions : Registering converter from interface java.util.Map to class org.springframework.data.geo.Point as reading converter although it doesn't convert from a store-supported type! You might want to check your annotation setup at the converter implementation.
2020-09-01 14:10:38.503 WARN 99192 --- [ main] o.s.data.convert.CustomConversions : Registering converter from class org.springframework.data.elasticsearch.core.geo.GeoPoint to interface java.util.Map as writing converter although it doesn't convert to a store-supported type! You might want to check your annotation setup at the converter implementation.
2020-09-01 14:10:38.503 WARN 99192 --- [ main] o.s.data.convert.CustomConversions : Registering converter from interface java.util.Map to class org.springframework.data.elasticsearch.core.geo.GeoPoint as reading converter although it doesn't convert from a store-supported type! You might want to check your annotation setup at the converter implementation.
2020-09-01 14:10:38.604 INFO 99192 --- [ main] o.s.d.elasticsearch.support.VersionInfo : Version Spring Data Elasticsearch: 4.0.3.RELEASE
2020-09-01 14:10:38.604 INFO 99192 --- [ main] o.s.d.elasticsearch.support.VersionInfo : Version Elasticsearch Client in build: 7.6.2
2020-09-01 14:10:38.605 INFO 99192 --- [ main] o.s.d.elasticsearch.support.VersionInfo : Version Elasticsearch Client used: 7.6.2
2020-09-01 14:10:38.605 INFO 99192 --- [ main] o.s.d.elasticsearch.support.VersionInfo : Version Elasticsearch cluster: 6.8.4
2020-09-01 14:10:38.605 WARN 99192 --- [ main] o.s.d.elasticsearch.support.VersionInfo : Version mismatch in between Elasticsearch Client and Cluster: 7.6.2 - 6.8.4
2020-09-01 14:10:38.688 INFO 99192 --- [ main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat started on port(s): 9898 (http) with context path ''
2020-09-01 14:10:38.698 INFO 99192 --- [ main] com.quan.sbrabbit.SbrabbitApplication : Started SbrabbitApplication in 16.941 seconds (JVM running for 22.495)
org.springframework.boot.SpringApplication@4a163575
监听到applicationStartedEvent

自定义事件：必须继承抽象类ApplicationEvent

public class QuanEvent extends ApplicationEvent {

/\*\*  
 \* 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 QuanEvent(String source) {  
    super(source);  
    System.out.println("事件  "+source);  
}

}

自定义监听器：监听自己定义的事件

public class QuanListenerQuanEvent implements ApplicationListener {
@Override
public void onApplicationEvent(QuanEvent event) {
System.out.println("监听到QuanEvent");

}

}

在完成springboot启动事件ApplicationStaredEvent中发布事件：

public class QuanListenerStartedEvent implements ApplicationListener {
@Override
public void onApplicationEvent(ApplicationStartedEvent event) {
event.getApplicationContext().publishEvent(new QuanEvent("hello"));
}
}

最后加上监听器的配置:
在spring.factories追加：

,com.quan.sbrabbit.Listener.QuanListenerQuanEvent

运行结果：

也可以使用注解进行监听器的编写（这时候只需要将监听器加载到bean容器里面就行，）

使用注解@EventListener

@Component
public class QuanListenerQuanEvent {
@EventListener
public void onApplicationEvent(QuanEvent event) {
System.out.println("监听到QuanEvent");

}

}

监听事件的原理：

@FunctionalInterface
public interface ApplicationListener extends EventListener {

/\*\*  
 \* Handle an application event.  
 \* @param event the event to respond to  
 \*/  
void onApplicationEvent(E event);

}

监听器触发机制：

SpringApplication-run 方法
public ConfigurableApplicationContext run(String… args){
SpringApplicationRunListeners listeners = getRunListeners(args);
listeners.starting();
}
进入starting方法到SpringApplicationRunListener类
void starting() {
for (SpringApplicationRunListener listener : this.listeners) {
listener.starting();
}
}
遍历所有的SpringApplicationRunListener

再进入starting：来到EventPublishingRunListener类：
@Override
public void starting() {
this.initialMulticaster.multicastEvent(new ApplicationStartingEvent(this.application, this.args));
}
调用广播器发送

进入multicastEvent方法属于这个类：SimpleApplicationEventMulticaster
@Override
public void multicastEvent(final ApplicationEvent event, @Nullable ResolvableType eventType) {
ResolvableType type = (eventType != null ? eventType : resolveDefaultEventType(event));
Executor executor = getTaskExecutor(); //获得线程池
for (ApplicationListener listener : getApplicationListeners(event, type)) {//获取对当前event感兴趣的监听器列表
if (executor != null) {
executor.execute(() -> invokeListener(listener, event));
}
else {
invokeListener(listener, event);
}
}
}

进入getApplicationListeners方法到类AbstractApplicationEventMulticaster
protected Collection> getApplicationListeners(
ApplicationEvent event, ResolvableType eventType) {

    Object source = event.getSource();//获得事件来源

其实source就是SpringApplication

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