Spring-Cloud中AbstractAutoServiceRegistration的“bug“

java-web

前话：zipkin-server与nacos结合时的坑

参考github解决方案

在解决Nacos的issue——对接zipkin时，遇到了一个奇怪的问题，当采用github的解决方案，即采用eureka-client时，zipkin-server能够自动注册到Eureka Server中，但是当采用nacos-discovery时，却怎么也无法实现zipkin-server服务自动注册到nacos-server中，通过断点调试以及参考Spring Cloud相关源码以及文档，终于发现了问题所在

Spring-Cloud认为服务自动注册的时机

SpringCloud本身认为服务的注册时机，应该是WebServerInitializedEvent事件发生后，进行服务的自动注册，因为在接收到此事件时，会下发bind(Event)操作，由start()函数内部调用register()实现服务的自动注册

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@Override
@SuppressWarnings("deprecation")
public void onApplicationEvent(WebServerInitializedEvent event) {
		bind(event);
}

@Deprecated
public void bind(WebServerInitializedEvent event) {
		ApplicationContext context = event.getApplicationContext();
		if (context instanceof ConfigurableWebServerApplicationContext) {
			if ("management".equals(((ConfigurableWebServerApplicationContext) context)
					.getServerNamespace())) {
				return;
			}
		}
		this.port.compareAndSet(0, event.getWebServer().getPort());
		this.start();
}

public void start() {
		if (!isEnabled()) {
			if (logger.isDebugEnabled()) {
				logger.debug("Discovery Lifecycle disabled. Not starting");
			}
			return;
		}

		// only initialize if nonSecurePort is greater than 0 and it isn't already running
		// because of containerPortInitializer below
		if (!this.running.get()) {
			this.context.publishEvent(
					new InstancePreRegisteredEvent(this, getRegistration()));
			register();
			if (shouldRegisterManagement()) {
				registerManagement();
			}
			this.context.publishEvent(
					new InstanceRegisteredEvent<>(this, getConfiguration()));
			this.running.compareAndSet(false, true);
		}

}

存在的问题

由上面的代码可知，SpringCloud本身对于服务注册的时机，是在发生WebServerInitializedEvent事件之后，才会去调用相应的register()方法实现服务注册，但是这里就可能存在一个小小的问题了。

在创建SpringBoot Web Application时，有一段代码比较关键

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protected ConfigurableApplicationContext createApplicationContext() {
		Class<?> contextClass = this.applicationContextClass;
		if (contextClass == null) {
			try {
				switch (this.webApplicationType) {
				case SERVLET:
					contextClass = Class.forName(DEFAULT_SERVLET_WEB_CONTEXT_CLASS);
					break;
				case REACTIVE:
					contextClass = Class.forName(DEFAULT_REACTIVE_WEB_CONTEXT_CLASS);
					break;
				default:
					contextClass = Class.forName(DEFAULT_CONTEXT_CLASS);
				}
			}
			catch (ClassNotFoundException ex) {
				throw new IllegalStateException(
						"Unable create a default ApplicationContext, "
								+ "please specify an ApplicationContextClass",
						ex);
			}
		}
		return (ConfigurableApplicationContext) BeanUtils.instantiateClass(contextClass);
}

因此，这里的contextClass对应着三种不同的类型，分别是AnnotationConfigServletWebServerApplicationContext、AnnotationConfigReactiveWebServerApplicationContext以及AnnotationConfigApplicationContext，而这三个中，只有前面两个Context会触发WebServerInitializedEvent事件的下发

AnnotationConfigServletWebServerApplicationContext

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@Override
protected void finishRefresh() {
		super.finishRefresh();
		WebServer webServer = startWebServer();
		if (webServer != null) {
			publishEvent(new ServletWebServerInitializedEvent(webServer, this));
		}
}

public class ServletWebServerInitializedEvent extends WebServerInitializedEvent {
    ...
}

AnnotationConfigReactiveWebServerApplicationContext

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@Override
protected void finishRefresh() {
		super.finishRefresh();
		WebServer webServer = startReactiveWebServer();
		if (webServer != null) {
			publishEvent(new ReactiveWebServerInitializedEvent(webServer, this));
		}
}

public class ReactiveWebServerInitializedEvent extends WebServerInitializedEvent {
    ...
}

AnnotationConfigApplicationContext

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protected void finishRefresh() {
		// Clear context-level resource caches (such as ASM metadata from scanning).
		clearResourceCaches();

		// Initialize lifecycle processor for this context.
		initLifecycleProcessor();

		// Propagate refresh to lifecycle processor first.
		getLifecycleProcessor().onRefresh();

		// Publish the final event.
		publishEvent(new ContextRefreshedEvent(this));

		// Participate in LiveBeansView MBean, if active.
		LiveBeansView.registerApplicationContext(this);
}

public class ContextRefreshedEvent extends ApplicationContextEvent {
    ...
}

因此，如果设置了spring.main.web-application-type=none时，createApplicationContext代码中的switch分支就会执行contextClass = Class.forName(DEFAULT_CONTEXT_CLASS);语句，此时获取到的Context为AnnotationConfigApplicationContext，而AnnotationConfigApplicationContext调用的finishRefresh方法所下发的事件ContextRefreshedEvent是没有继承WebServerInitializedEvent的，在这种情况下，SpringCloud就无法执行服务自动注册

进行调整

调整的方法很简单，由于SpringBoot采用事件机制，因此当整个SpringBoot Application程序初始化完毕，执行listeners.running(context)时，会触发ApplicationReadyEvent事件

SpringApplication

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public ConfigurableApplicationContext run(String... args) {
		StopWatch stopWatch = new StopWatch();
		stopWatch.start();
		...

		try {
			listeners.running(context);
		}
		catch (Throwable ex) {
			handleRunFailure(context, ex, exceptionReporters, null);
			throw new IllegalStateException(ex);
		}
		return context;
}

EventPublishingRunListener

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@Override
public void running(ConfigurableApplicationContext context) {
		context.publishEvent(
				new ApplicationReadyEvent(this.application, this.args, context));
}

因此，只需要改动如下代码即可

org.springframework.cloud.client.serviceregistry.AbstractAutoServiceRegistration

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public abstract class AbstractAutoServiceRegistration<R extends Registration>
		implements AutoServiceRegistration, ApplicationContextAware,
		ApplicationListener<ApplicationReadyEvent> {
    ...
}

更改事件监听类型为ApplicationReadyEvent即可