Dubbo学习-8-dubbo启动时检查

启动时检查的作用如下：

（1）Dubbo 缺省会在启动时检查依赖的服务是否可用，不可用时会抛出异常，阻止 Spring 初始化完成，以便上线时，能及早发现问题，默认 check="true"。

（2）可以通过 check="false" 关闭检查，比如，测试时，有些服务不关心，或者出现了循环依赖，必须有一方先启动的情况下

（3）如果你的 Spring 容器是懒加载的，或者通过 API 编程延迟引用服务，请关闭 check，否则服务临时不可用时，会抛出异常，拿到 null 引用，如果 check="false"，总是会返回引用，当服务恢复时，能自动连上。

以前面帖子工程为例：

直接启动服务的消费者：order-service-consumer工程，结果如下：'

具体错误信息如下：提示没有提供者

 Exception in thread "main" org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'orderServiceImpl': Unsatisfied dependency expressed through field 'userService'; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'userService': FactoryBean threw exception on object creation; nested exception is java.lang.IllegalStateException: Failed to check the status of the service com.lch.test.service.UserService. No provider available for the service com.lch.test.service.UserService from the url zookeeper://127.0.0.1:2181/com.alibaba.dubbo.registry.RegistryService?anyhost=true&application=order-service-consumer&check=false&dubbo=2.6.2&generic=false&interface=com.lch.test.service.UserService&methods=getUserAddressList&pid=8740&register.ip=192.168.0.110&remote.timestamp=1563206416952&side=consumer&timestamp=1563370847797 to the consumer 192.168.0.110 use dubbo version 2.6.2
     at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:588)
     at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:88)
     at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:366)
     at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1268)
     at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:553)
     at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:483)
     at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:312)
     at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230)
     at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:308)
     at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:197)
     at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:761)
     at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:867)
     at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:543)
     at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:139)
     at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:83)
     at com.lch.test.MainApplication.main(MainApplication.java:12)
 Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'userService': FactoryBean threw exception on object creation; nested exception is java.lang.IllegalStateException: Failed to check the status of the service com.lch.test.service.UserService. No provider available for the service com.lch.test.service.UserService from the url zookeeper://127.0.0.1:2181/com.alibaba.dubbo.registry.RegistryService?anyhost=true&application=order-service-consumer&check=false&dubbo=2.6.2&generic=false&interface=com.lch.test.service.UserService&methods=getUserAddressList&pid=8740&register.ip=192.168.0.110&remote.timestamp=1563206416952&side=consumer&timestamp=1563370847797 to the consumer 192.168.0.110 use dubbo version 2.6.2
     at org.springframework.beans.factory.support.FactoryBeanRegistrySupport.doGetObjectFromFactoryBean(FactoryBeanRegistrySupport.java:177)
     at org.springframework.beans.factory.support.FactoryBeanRegistrySupport.getObjectFromFactoryBean(FactoryBeanRegistrySupport.java:103)
     at org.springframework.beans.factory.support.AbstractBeanFactory.getObjectForBeanInstance(AbstractBeanFactory.java:1640)
     at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:254)
     at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:202)
     at org.springframework.beans.factory.config.DependencyDescriptor.resolveCandidate(DependencyDescriptor.java:208)
     at org.springframework.beans.factory.support.DefaultListableBeanFactory.addCandidateEntry(DefaultListableBeanFactory.java:1316)
     at org.springframework.beans.factory.support.DefaultListableBeanFactory.findAutowireCandidates(DefaultListableBeanFactory.java:1282)
     at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1101)
     at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1066)
     at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:585)
     ... 15 more
 Caused by: java.lang.IllegalStateException: Failed to check the status of the service com.lch.test.service.UserService. No provider available for the service com.lch.test.service.UserService from the url zookeeper://127.0.0.1:2181/com.alibaba.dubbo.registry.RegistryService?anyhost=true&application=order-service-consumer&check=false&dubbo=2.6.2&generic=false&interface=com.lch.test.service.UserService&methods=getUserAddressList&pid=8740&register.ip=192.168.0.110&remote.timestamp=1563206416952&side=consumer&timestamp=1563370847797 to the consumer 192.168.0.110 use dubbo version 2.6.2
     at com.alibaba.dubbo.config.ReferenceConfig.createProxy(ReferenceConfig.java:422)
     at com.alibaba.dubbo.config.ReferenceConfig.init(ReferenceConfig.java:333)
     at com.alibaba.dubbo.config.ReferenceConfig.get(ReferenceConfig.java:163)
     at com.alibaba.dubbo.config.spring.ReferenceBean.getObject(ReferenceBean.java:66)
     at org.springframework.beans.factory.support.FactoryBeanRegistrySupport.doGetObjectFromFactoryBean(FactoryBeanRegistrySupport.java:170)
     ... 25 more

这是因为，如果没有配置启动检查，dubbo是默认进行启动检查的，也就是启动服务的消费者时，先检查服务的提供者有没有启动起来。

修改配置文件,在dubboLreference标签里面加上  check=“false”

 <?xml version="1.0" encoding="UTF-8"?>
 <beans xmlns="http://www.springframework.org/schema/beans"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xmlns:dubbo="http://dubbo.apache.org/schema/dubbo"
     xmlns:context="http://www.springframework.org/schema/context"
     xsi:schemaLocation="http://www.springframework.org/schema/beans
            http://www.springframework.org/schema/beans/spring-beans-4.3.xsd
            http://dubbo.apache.org/schema/dubbo
            http://dubbo.apache.org/schema/dubbo/dubbo.xsd
            http://www.springframework.org/schema/context
            http://www.springframework.org/schema/context/spring-context.xsd">

     <!--扫描包注解 -->
     <context:component-scan
         base-package="com.lch.test.service.impl" />

     <!-- 1.消费方应用名 -->
     <dubbo:application name="order-service-consumer"  />

     <!-- 2.指定注册中心地址 -->
     <dubbo:registry address="zookeeper://127.0.0.1:2181" />

     <!-- 生成远程服务代理dubbo:reference：声明需要调用的远程服务的接口 -->
     <!-- user-service-provider工程里面暴露了一个名为userService的服务，这里要引用这个服务 -->
     <dubbo:reference id="userService"
26         interface="com.lch.test.service.UserService" check="false"/>

     <!-- 连接监控中心：使用自动发现的方式 -->
     <dubbo:monitor protocol="register" />
     <!-- 直连注册中心 -->
     <!-- <dubbo:monitor address="127.0.0.1:7070" /> -->

 </beans>

然后再启动服务的消费者：

dubbo启动时检查可以配置三种作用范围,上面例子是仅仅关闭对user-service-provider这个服务提供者的检查，如果要关闭所有服务消费者对 与其对应的服务提供者的检查，

可以在标签 dubbo:consumer 中添加check="false" 即：  <dubbo:consumer check="false" />