dubbo消费者启动报错分析
环境
os: MacBook Produbbo: 2.7.5java: 1.8问题
运行dubbo-demo-xml-consumer项目，控制台报以下错误:
java.lang.IllegalStateException: There's no ApplicationConfig specified. at org.apache.dubbo.config.context.ConfigManager.lambda$getApplicationOrElseThrow$0(ConfigManager.java:88) at java.util.Optional.orElseThrow(Optional.java:290) at org.apache.dubbo.config.context.ConfigManager.getApplicationOrElseThrow(ConfigManager.java:88) at org.apache.dubbo.rpc.model.ApplicationModel.getApplicationConfig(ApplicationModel.java:100) at org.apache.dubbo.registry.integration.RegistryProtocol.destroy(RegistryProtocol.java:500) at org.apache.dubbo.rpc.protocol.ProtocolFilterWrapper.destroy(ProtocolFilterWrapper.java:166) at org.apache.dubbo.rpc.protocol.ProtocolListenerWrapper.destroy(ProtocolListenerWrapper.java:80) at org.apache.dubbo.config.DubboShutdownHook.destroyProtocols(DubboShutdownHook.java:140) at org.apache.dubbo.config.DubboShutdownHook.destroyAll(DubboShutdownHook.java:124) at org.apache.dubbo.config.bootstrap.DubboBootstrap.destroy(DubboBootstrap.java:1037) at org.apache.dubbo.config.bootstrap.DubboBootstrap.stop(DubboBootstrap.java:817) at org.apache.dubbo.config.spring.context.DubboBootstrapApplicationListener.onContextClosedEvent(DubboBootstrapApplicationListener.java:65) at org.apache.dubbo.config.spring.context.DubboBootstrapApplicationListener.onApplicationContextEvent(DubboBootstrapApplicationListener.java:55) at org.apache.dubbo.config.spring.context.OneTimeExecutionApplicationContextEventListener.onApplicationEvent(OneTimeExecutionApplicationContextEventListener.java:40) at org.springframework.context.event.SimpleApplicationEventMulticaster.doInvokeListener(SimpleApplicationEventMulticaster.java:172) at org.springframework.context.event.SimpleApplicationEventMulticaster.invokeListener(SimpleApplicationEventMulticaster.java:165) at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:139) at org.springframework.context.support.AbstractApplicationContext.publishEvent(AbstractApplicationContext.java:393) at org.springframework.context.support.AbstractApplicationContext.publishEvent(AbstractApplicationContext.java:347) at org.springframework.context.support.AbstractApplicationContext.doClose(AbstractApplicationContext.java:991) at org.springframework.context.support.AbstractApplicationContext$2.run(AbstractApplicationContext.java:929)根据打印出来的日志，方法调用栈为
通过图可知 org.apache.dubbo.registry.integration.RegistryProtocol#destroy该方法都会在 org.apache.dubbo.config.bootstrap.DubboBootstrap#destroy中被调用，而且是通过Spring ContextClosedEvent事件(容器关闭时)、JVM钩子函数(JVM退出)触发。报错的具体位置，在方法 org.apache.dubbo.config.context.ConfigManager#getApplicationOrElseThrow中，通过断点分析 org.apache.dubbo.config.context.ConfigManager#getConfig(java.lang.String)中获取配置信息时， configsCache为空，所以该方法的返回值为null，上层方法就报错了。
protected <C extends AbstractConfig> C getConfig(String configType) throws IllegalStateException { return read(() -> { Map<String, C> configsMap = (Map) configsCache.getOrDefault(configType, emptyMap()); int size = configsMap.size(); if (size < 1) {// throw new IllegalStateException("No such " + configType.getName() + " is found"); return null; } else if (size > 1) { logger.warn("Expected single matching of " + configType + ", but found " + size + " instances, will randomly pick the first one."); }
return configsMap.values().iterator().next(); }); }已经定位到报错的位置，奇怪的是，运行dubbo-demo-api-consumer项目时，却不报错，那具体原因是什么呢？
分析
configsCache什么时候会被删除呢，通过代码可发现，在 org.apache.dubbo.config.context.ConfigManager#clear方法中会删除：
public void clear() { write(() -> { this.configsCache.clear(); }); }而该方法只会在 org.apache.dubbo.config.bootstrap.DubboBootstrap#clearConfigs中被调用(除单元测试外)，该方法的调用栈:
通过调用栈发现 org.apache.dubbo.config.context.ConfigManager#clear也会在 org.apache.dubbo.config.bootstrap.DubboBootstrap#destroy被调用，而 destroy同样会被Spring ContextClosedEvent事件(容器关闭时)、JVM钩子函数(JVM退出)触发。到这里，猜想: 在dubbo-demo-xml-consumer中运行程序结束后，Spring容器关闭时，会触发ContextClosedEvent事件[A]，而JVM退出时也会触发钩子函数[B]，两个都会去销毁缓存的配置信息等，存在[A]销毁了配置信息，即上文中 configsCache，而[B]此时从缓存中没有获取到配置就会报错，实际通过断点调试确实如此。
总结
虽然这个错误不会导致程序的结果，但是报错的确让人很疑惑，如果不深入分析很难找到问题所在。