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Spring Cloud Config提供了一个ConfigClientWatch功能，可以定时轮询客户端配置的状态，如果状态发生变化，则refresh。

配置文件

spring:  cloud:    config:      uri: http://localhost:8888      watch:        enabled: true        initialDelay: 5000 ##default 180000 ms        delay: 10000 ##default 500 ms

配置类

spring-cloud-config-client-1.3.1.RELEASE-sources.jar!/org/springframework/cloud/config/client/ConfigClientAutoConfiguration.java

@Configuration    @ConditionalOnClass(ContextRefresher.class)    @ConditionalOnBean(ContextRefresher.class)    @ConditionalOnProperty(value = "spring.cloud.config.watch.enabled")    protected static class ConfigClientWatchConfiguration {        @Bean        public ConfigClientWatch configClientWatch(ContextRefresher contextRefresher) {            return new ConfigClientWatch(contextRefresher);        }    }

ConfigClientWatch

public class ConfigClientWatch implements Closeable, EnvironmentAware {    private static Log log = LogFactory            .getLog(ConfigServicePropertySourceLocator.class);    private final AtomicBoolean running = new AtomicBoolean(false);    private final ContextRefresher refresher;    private Environment environment;    public ConfigClientWatch(ContextRefresher refresher) {        this.refresher = refresher;    }    @Override    public void setEnvironment(Environment environment) {        this.environment = environment;    }    @PostConstruct    public void start() {        this.running.compareAndSet(false, true);    }    @Scheduled(initialDelayString = "${spring.cloud.config.watch.initialDelay:180000}", fixedDelayString = "${spring.cloud.config.watch.delay:500}")    public void watchConfigServer() {        if (this.running.get()) {            String newState = this.environment.getProperty("config.client.state");            String oldState = ConfigClientStateHolder.getState();            // only refresh if state has changed            if (stateChanged(oldState, newState)) {                ConfigClientStateHolder.setState(newState);                this.refresher.refresh();            }        }    }    /* for testing */ boolean stateChanged(String oldState, String newState) {        return (!hasText(oldState) && hasText(newState))                || (hasText(oldState) && !oldState.equals(newState));    }    @Override    public void close() {        this.running.compareAndSet(true, false);    }}

依赖config.client.state的环境变量，来判断client端配置文件的状态

依赖ContextRefresher去刷新配置/实例

ContextRefresher

spring-cloud-context-1.2.2.RELEASE-sources.jar!/org/springframework/cloud/context/refresh/ContextRefresher.java

public synchronized Set
    
      refresh() {        Map
     
       before = extract(                this.context.getEnvironment().getPropertySources());        addConfigFilesToEnvironment();        Set
      
        keys = changes(before,                extract(this.context.getEnvironment().getPropertySources())).keySet();        this.context.publishEvent(new EnvironmentChangeEvent(keys));        this.scope.refreshAll();        return keys;    }
      
     
    

这个refresh主要做两件事情:

• 第一件是发布EnvironmentChangeEvent事件

• 第二件是调用RefreshScope的refreshAll方法

EnvironmentChangeEvent的listener

spring-cloud-context-1.2.2.RELEASE-sources.jar!/org/springframework/cloud/context/properties/ConfigurationPropertiesRebinder.java

@Component@ManagedResourcepublic class ConfigurationPropertiesRebinder        implements ApplicationContextAware, ApplicationListener
    
      {    private ConfigurationPropertiesBeans beans;    private ConfigurationPropertiesBindingPostProcessor binder;    private ApplicationContext applicationContext;    private Map
     
       errors = new ConcurrentHashMap<>();    public ConfigurationPropertiesRebinder(            ConfigurationPropertiesBindingPostProcessor binder,            ConfigurationPropertiesBeans beans) {        this.binder = binder;        this.beans = beans;    }    @Override    public void setApplicationContext(ApplicationContext applicationContext)            throws BeansException {        this.applicationContext = applicationContext;    }    /**     * A map of bean name to errors when instantiating the bean.     *     * @return the errors accumulated since the latest destroy     */    public Map
      
        getErrors() {        return this.errors;    }    @ManagedOperation    public void rebind() {        this.errors.clear();        for (String name : this.beans.getBeanNames()) {            rebind(name);        }    }    @ManagedOperation    public boolean rebind(String name) {        if (!this.beans.getBeanNames().contains(name)) {            return false;        }        if (this.applicationContext != null) {            try {                Object bean = this.applicationContext.getBean(name);                if (AopUtils.isCglibProxy(bean)) {                    bean = getTargetObject(bean);                }                this.binder.postProcessBeforeInitialization(bean, name);                this.applicationContext.getAutowireCapableBeanFactory()                        .initializeBean(bean, name);                return true;            }            catch (RuntimeException e) {                this.errors.put(name, e);                throw e;            }        }        return false;    }    @SuppressWarnings("unchecked")    private static 
       
         T getTargetObject(Object candidate) {        try {            if (AopUtils.isAopProxy(candidate) && (candidate instanceof Advised)) {                return (T) ((Advised) candidate).getTargetSource().getTarget();            }        }        catch (Exception ex) {            throw new IllegalStateException("Failed to unwrap proxied object", ex);        }        return (T) candidate;    }    @ManagedAttribute    public Set
        
          getBeanNames() {        return new HashSet
         
          (this.beans.getBeanNames()); } @Override public void onApplicationEvent(EnvironmentChangeEvent event) { rebind(); }}
         
        
       
      
     
    

RefreshScope的refreshAll

spring-cloud-context-1.2.2.RELEASE-sources.jar!/org/springframework/cloud/context/scope/refresh/RefreshScope.java

@ManagedOperation(description = "Dispose of the current instance of all beans in this scope and force a refresh on next method execution.")    public void refreshAll() {        super.destroy();        this.context.publishEvent(new RefreshScopeRefreshedEvent());    }

发布RefreshScopeRefreshedEvent事件

RefreshScopeRefreshedEvent事件listener

spring-cloud-netflix-eureka-client-1.3.1.RELEASE-sources.jar!/org/springframework/cloud/netflix/eureka/EurekaDiscoveryClientConfiguration.java

@Configuration    @ConditionalOnClass(RefreshScopeRefreshedEvent.class)    protected static class EurekaClientConfigurationRefresher {        @Autowired(required = false)        private EurekaClient eurekaClient;        @Autowired(required = false)        private EurekaAutoServiceRegistration autoRegistration;        @EventListener(RefreshScopeRefreshedEvent.class)        public void onApplicationEvent(RefreshScopeRefreshedEvent event) {            //This will force the creation of the EurkaClient bean if not already created            //to make sure the client will be reregistered after a refresh event            if(eurekaClient != null) {                eurekaClient.getApplications();            }            if (autoRegistration != null) {                // register in case meta data changed                this.autoRegistration.stop();                this.autoRegistration.start();            }        }    }

spring-cloud-netflix-core-1.2.6.RELEASE-sources.jar!/org/springframework/cloud/netflix/zuul/ZuulConfiguration.java

@Bean    public ApplicationListener
    
      zuulRefreshRoutesListener() {        return new ZuulRefreshListener();    }private static class ZuulRefreshListener            implements ApplicationListener
     
       {        @Autowired        private ZuulHandlerMapping zuulHandlerMapping;        private HeartbeatMonitor heartbeatMonitor = new HeartbeatMonitor();        @Override        public void onApplicationEvent(ApplicationEvent event) {            if (event instanceof ContextRefreshedEvent                    || event instanceof RefreshScopeRefreshedEvent                    || event instanceof RoutesRefreshedEvent) {                this.zuulHandlerMapping.setDirty(true);            }            else if (event instanceof HeartbeatEvent) {                if (this.heartbeatMonitor.update(((HeartbeatEvent) event).getValue())) {                    this.zuulHandlerMapping.setDirty(true);                }            }        }    }
     
    

小结

Spring Cloud Config的代码是有提供ConfigClientWatch，但是实际单纯使用git作为config server的时候，拉取配置的时候得到的state始终是null，因此客户端轮询是起不到刷新效果的。第二个就是这个refresh发布的RefreshScopeRefreshedEvent，eureka会先去更新注册信息为DOWN，然后再UP起来，这个频繁操作有点风险。