背景介绍
最近把dubbo的版本从2.7.3升级到2.7.15时，遇到一个报错 No application config found or it's not a valid config! ，对应的异常栈为：
Caused by: java.lang.IllegalStateException: No application config found or it's not a valid config! Please add <dubbo:application name="..." /> to your spring config. at org.apache.dubbo.config.utils.ConfigValidationUtils.validateApplicationConfig(ConfigValidationUtils.java:419) ~[dubbo-2.7.15.jar:2.7.15] at org.apache.dubbo.config.bootstrap.DubboBootstrap.checkGlobalConfigs(DubboBootstrap.java:539) ~[dubbo-2.7.15.jar:2.7.15] at org.apache.dubbo.config.bootstrap.DubboBootstrap.initialize(DubboBootstrap.java:525) ~[dubbo-2.7.15.jar:2.7.15] at org.apache.dubbo.config.ReferenceConfig.init(ReferenceConfig.java:244) ~[dubbo-2.7.15.jar:2.7.15] at org.apache.dubbo.config.ReferenceConfig.get(ReferenceConfig.java:206) ~[dubbo-2.7.15.jar:2.7.15] at org.apache.dubbo.config.spring.ReferenceBean.getObject(ReferenceBean.java:68) ~[dubbo-2.7.15.jar:2.7.15] at org.springframework.beans.factory.support.FactoryBeanRegistrySupport.doGetObjectFromFactoryBean(FactoryBeanRegistrySupport.java:171) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE] at org.springframework.beans.factory.support.FactoryBeanRegistrySupport.getObjectFromFactoryBean(FactoryBeanRegistrySupport.java:101) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE] at org.springframework.beans.factory.support.AbstractBeanFactory.getObjectForBeanInstance(AbstractBeanFactory.java:1818) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.getObjectForBeanInstance(AbstractAutowireCapableBeanFactory.java:1266) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE] at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:260) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE] at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:207) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.resolveBeanByName(AbstractAutowireCapableBeanFactory.java:454) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE] at org.springframework.context.annotation.CommonAnnotationBeanPostProcessor.autowireResource(CommonAnnotationBeanPostProcessor.java:543) ~[spring-context-5.2.0.RELEASE.jar:5.2.0.RELEASE] at org.springframework.context.annotation.CommonAnnotationBeanPostProcessor.getResource(CommonAnnotationBeanPostProcessor.java:513) ~[spring-context-5.2.0.RELEASE.jar:5.2.0.RELEASE] at org.springframework.context.annotation.CommonAnnotationBeanPostProcessor$ResourceElement.getResourceToInject(CommonAnnotationBeanPostProcessor.java:653) ~[spring-context-5.2.0.RELEASE.jar:5.2.0.RELEASE] at org.springframework.beans.factory.annotation.InjectionMetadata$InjectedElement.inject(InjectionMetadata.java:224) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE] at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:116) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE] at org.springframework.context.annotation.CommonAnnotationBeanPostProcessor.postProcessProperties(CommonAnnotationBeanPostProcessor.java:334) ~[spring-context-5.2.0.RELEASE.jar:5.2.0.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1429) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:594) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:517) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE] at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:323) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE] at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE] at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:321) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE] at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:202) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE] at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:400) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateUsingFactoryMethod(AbstractAutowireCapableBeanFactory.java:1338) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1177) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:557) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:517) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE] at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:323) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE] at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE] at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:321) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE] at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:202) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE] at org.springframework.beans.factory.config.DependencyDescriptor.resolveCandidate(DependencyDescriptor.java:276) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE] at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1287) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE] at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1207) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE] at org.springframework.beans.factory.support.ConstructorResolver.resolveAutowiredArgument(ConstructorResolver.java:874) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE] at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:778) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE] at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:528) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateUsingFactoryMethod(AbstractAutowireCapableBeanFactory.java:1338) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1177) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:557) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:517) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE] at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:323) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE] at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE] at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:321) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE] at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:207) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE] at org.springframework.aop.framework.autoproxy.BeanFactoryAdvisorRetrievalHelper.findAdvisorBeans(BeanFactoryAdvisorRetrievalHelper.java:91) ~[spring-aop-5.2.0.RELEASE.jar:5.2.0.RELEASE] at org.springframework.aop.framework.autoproxy.AbstractAdvisorAutoProxyCreator.findCandidateAdvisors(AbstractAdvisorAutoProxyCreator.java:109) ~[spring-aop-5.2.0.RELEASE.jar:5.2.0.RELEASE] at org.springframework.aop.aspectj.annotation.AnnotationAwareAspectJAutoProxyCreator.findCandidateAdvisors(AnnotationAwareAspectJAutoProxyCreator.java:92) ~[spring-aop-5.2.0.RELEASE.jar:5.2.0.RELEASE] at org.springframework.aop.aspectj.autoproxy.AspectJAwareAdvisorAutoProxyCreator.shouldSkip(AspectJAwareAdvisorAutoProxyCreator.java:101) ~[spring-aop-5.2.0.RELEASE.jar:5.2.0.RELEASE] at org.springframework.aop.framework.autoproxy.AbstractAutoProxyCreator.postProcessBeforeInstantiation(AbstractAutoProxyCreator.java:251) ~[spring-aop-5.2.0.RELEASE.jar:5.2.0.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyBeanPostProcessorsBeforeInstantiation(AbstractAutowireCapableBeanFactory.java:1141) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.resolveBeforeInstantiation(AbstractAutowireCapableBeanFactory.java:1114) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:506) ~[spring-beans-5.2.0.RELEASE.jar:5.2.0.RELEASE] ... 12 more
其中，我们使用 Springboot 版本是2.2.0。
于是手动跟踪调试了下，发现某些后置处理器执行时，在解决它的依赖时，会去创建 dubbo 服务的 bean，然后就会创建 ApplicationConfig 对象了。注意这个对象其实只是new了一下，所有属性都是默认值，并非来源于我们定义的 dubbo 配置文件。
而我们定义的 dubbo 配置文件，是在 ApplicationConfig 中的 addIntoConfigManager 中注入的：
public abstract class AbstractConfig implements Serializable {
...
@PostConstruct
public void addIntoConfigManager() {
ApplicationModel.getConfigManager().addConfig(this);
}
...
}
其中，@PostConstruct 注解会由 CommonAnnotationBeanPostProcessor 这个后置处理器（继承自 InitDestroyAnnotationBeanPostProcessor）解析执行。但很遗憾，此时它还没有被执行，因此也就没有把正确的dubbo配置注入进去，最终导致dubbo框架在校验时发现无效配置，继而报错。
网上相关讨论及解决方案
关于这类报错，网上也有不少讨论，如：
-
No application config found or it's not a valid config!
-
No registry config found or it's not a valid config!
-
同样的配置，2.7.3启动成功，2.7.6启动报错
简单总结起来，由于dubbo没有一个固定的初始化时机，而是与 ReferenceBean 等 dubbo 框架中的 beans 初始化相关。如果它们被过早初始化，导致某些 BeanPostProcessor 尚未被执行，就会出现dubbo配置丢失的问题。
自然，dubbo官方也注意到了这个问题，于是在3.x版本进行了改造，针对该问题做了优化，参见Dubbo 3 Spring相关优化。
但3.x做了大量重构，如果我们不想升级，应该怎么办呢？
其实根据上面提到的原因，我们可以自己定义一个后置处理器，拦截 dubbo 框架的 beans，并手动注入对应的配置。本质上来说，将之前来不及执行的注入代码提到前面去。这样，我们前面提到的「某些后置处理器执行时，在解决它的依赖时，会去创建 dubbo 服务的 bean，然后就会创建 ApplicationConfig 对象了」，就变成了「某些后置处理器执行时，在解决它的依赖时，会去创建 dubbo 服务的 bean，此时会被我们自定义的后置处理器拦截，并注入对应的dubbo配置，然后就会创建正确的 ApplicationConfig 对象」。
具体做法为：
step1. 定义一个后置处理器，识别到 bean 属于 AbstractConfig 配置后，将其注入：
package com.xxx;
import org.apache.dubbo.config.AbstractConfig;
import org.apache.dubbo.rpc.model.ApplicationModel;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;
public class DubboBeanPostProcessor implements BeanPostProcessor {
@Override
public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
if (bean instanceof AbstractConfig) {
AbstractConfig abstractConfig = (AbstractConfig) bean;
ApplicationModel.getConfigManager().addConfig(abstractConfig);
}
return BeanPostProcessor.super.postProcessAfterInitialization(bean, beanName);
}
}
step2. 定义一个 Initializer，并将刚才定义的 DubboBeanPostProcessor 注入：
package com.xxx;
import org.springframework.context.ApplicationContextInitializer;
import org.springframework.context.ConfigurableApplicationContext;
public class DubboApplicationContextInitializer
implements ApplicationContextInitializer<ConfigurableApplicationContext> {
@Override
public void initialize(ConfigurableApplicationContext applicationContext) {
applicationContext.getBeanFactory().addBeanPostProcessor(new DubboBeanPostProcessor());
}
}
step3. 把 DubboApplicationContextInitializer 注入到Spring框架中，可以采用多种方式。
方式1. 直接在启动类注入：
@ImportResource(locations = {"classpath:dubbo.xml"})
@SpringBootApplication(exclude = {DataSourceAutoConfiguration.class})
public class Launcher extends SpringBootServletInitializer {
public static void main(String[] args) {
SpringApplication springApplication = new SpringApplication(Launcher.class);
springApplication.addInitializers(new DubboApplicationContextInitializer());
springApplication.run(args);
}
}
方式2. 在 resources 的 META-INF 目录下配置 spring.factories 文件并写入：
org.springframework.context.ApplicationContextInitializer=com.xxx.DubboApplicationContextInitializer