EurekaClient自动装配及启动流程解析

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在上篇文章中, 我们简单介绍了 EurekaServer 自动装配及启动流程解析，本篇文章则继续研究 EurekaClient 的相关代码

老规矩，先看 spring.factories 文件，其中引入了一个配置类EurekaDiscoveryClientConfigServiceBootstrapConfiguration

@ConditionalOnClass(ConfigServicePropertySourceLocator.class)
@ConditionalOnProperty(value = "spring.cloud.config.discovery.enabled", matchIfMissing = false)
@Configuration
@Import({ EurekaDiscoveryClientConfiguration.class,
        EurekaClientAutoConfiguration.class })
public class EurekaDiscoveryClientConfigServiceBootstrapConfiguration {}

上方两个注解则是这个配置类是否能够开启的条件，这里就不再展开，直接看它引入的配置类吧

`EurekaDiscoveryClientConfiguration`

细心的读者可能会发现这里又注册了一个 Marker 类，可以猜测也是某个地方的开关
EurekaClientConfigurationRefresher这个类看名字就知道这是当配置被动态刷新时的一个处理器，这里也不再展开了
EurekaHealthCheckHandlerConfiguration这里面注册了一个 Eureka 健康检查的处理类，这个健康检查相关的原理分析可以参考这篇文章：SpringBoot 健康检查实现原理

`EurekaClientAutoConfiguration`

这个类里面全是重点，也是我们本文的核心

注解

@Configuration
@EnableConfigurationProperties
@ConditionalOnClass(EurekaClientConfig.class)
@Import(DiscoveryClientOptionalArgsConfiguration.class)
@ConditionalOnBean(EurekaDiscoveryClientConfiguration.Marker.class)
@ConditionalOnProperty(value = "eureka.client.enabled", matchIfMissing = true)
@AutoConfigureBefore({ NoopDiscoveryClientAutoConfiguration.class,
        CommonsClientAutoConfiguration.class, ServiceRegistryAutoConfiguration.class })
@AutoConfigureAfter(name = {"org.springframework.cloud.autoconfigure.RefreshAutoConfiguration",
        "org.springframework.cloud.netflix.eureka.EurekaDiscoveryClientConfiguration",
        "org.springframework.cloud.client.serviceregistry.AutoServiceRegistrationAutoConfiguration"})

首先可以看到这个类一共包含这些注解，我们来一一解析比较重要的几个注解吧

`@Import(DiscoveryClientOptionalArgsConfiguration.class)`

引入了两个 bean，RestTemplateDiscoveryClientOptionalArgs和MutableDiscoveryClientOptionalArgs，这两个类的作用暂且不说

`@ConditionalOnBean(EurekaDiscoveryClientConfiguration.Marker.class)`

刚才说的 Marker 类的作用出来了

`@AutoConfigureBefore`

既然必须在这三个类完成自动装配之后才能进行装配，那就代表着这三个类肯定大有用途，研究一下吧

`NoopDiscoveryClientAutoConfiguration`

故名思意，负责服务发现的类，咱们重点关注一下其中的几个方法

init

@PostConstruct
    public void init() {
        String host = "localhost";
        try {host = InetAddress.getLocalHost().getHostName();}
        catch (UnknownHostException e) {log.warn("Cannot get host info: (" + e.getMessage() + ")");
        }
        int port = findPort();
        this.serviceInstance = new DefaultServiceInstance(this.environment.getProperty("spring.application.name", "application"),
                host, port, false);
    }

这里构造了一个 DefaultServiceInstance 对象，这个对象包含了当前项目的 ip+ 端口 + 项目名称

注入 beanNoopDiscoveryClient

@Bean
    public DiscoveryClient discoveryClient() {return new NoopDiscoveryClient(this.serviceInstance);
    }

再深入看一下这个类

public class NoopDiscoveryClient implements DiscoveryClient {public NoopDiscoveryClient(ServiceInstance instance) { }

    @Override
    public String description() {return "Spring Cloud No-op DiscoveryClient";}

    @Override
    public List<ServiceInstance> getInstances(String serviceId) {return Collections.emptyList();
    }

    @Override
    public List<String> getServices() {return Collections.emptyList();
    }

}

这个类包含了获取当前实例以及当前服务的方法，但是返回的都是空，那么是不是会在后面的某个地方被覆盖呢？

`CommonsClientAutoConfiguration`

进去深入了解一下，哎哟，注册了几个 bean：DiscoveryClientHealthIndicator、DiscoveryCompositeHealthIndicator。原来是健康检查相关的东西，那就忽略了

`ServiceRegistryAutoConfiguration`

这个配置类中主要注册了一个 bean：ServiceRegistryEndpoint这个类主要是对外提供对与 Eureka 状态的检查

@ReadOperation
    public ResponseEntity getStatus() {if (this.registration == null) {return ResponseEntity.status(HttpStatus.NOT_FOUND).body("no registration found");
        }

        return ResponseEntity.ok().body(this.serviceRegistry.getStatus(this.registration));
    }

而 Eureka 的状态则是通过 serviceRegistry 对象获取的，这个对象会再下方详细分析

注册 bean

接着来看这个类注入的几个 bean

`EurekaClientConfigBean`

@Bean
    @ConditionalOnMissingBean(value = EurekaClientConfig.class, search = SearchStrategy.CURRENT)
    public EurekaClientConfigBean eurekaClientConfigBean(ConfigurableEnvironment env) {EurekaClientConfigBean client = new EurekaClientConfigBean();
        if ("bootstrap".equals(this.env.getProperty("spring.config.name"))) {client.setRegisterWithEureka(false);
        }
        return client;
    }

这个 bean 中包含了 eureka.client.xxx 系列的一些配置，详细的配置信息可以参考这里：https://github.com/shiyujun/s…

`EurekaInstanceConfigBean`

这个 bean 中主要是包含 eureka 实例（eureka.instance.xxx系列）的一些配置信息，详细的配置信息同上

`RefreshableEurekaClientConfiguration.DiscoveryClient`

        @Bean(destroyMethod = "shutdown")
        @ConditionalOnMissingBean(value = EurekaClient.class, search = SearchStrategy.CURRENT)
        @org.springframework.cloud.context.config.annotation.RefreshScope
        @Lazy
        public EurekaClient eurekaClient(ApplicationInfoManager manager, EurekaClientConfig config, EurekaInstanceConfig instance) {manager.getInfo(); // force initialization
            return new CloudEurekaClient(manager, config, this.optionalArgs,
                    this.context);
        }

其中 CloudEurekaClient 是DiscoveryClient的子类，而 DiscoveryClient 则是 EurekaClient 的核心类

       public CloudEurekaClient(ApplicationInfoManager applicationInfoManager,
                             EurekaClientConfig config,
                             AbstractDiscoveryClientOptionalArgs<?> args,
                             ApplicationEventPublisher publisher) {
                             // 这里会调用父类 DiscoveryClient 的构造方法
        super(applicationInfoManager, config, args);
        this.applicationInfoManager = applicationInfoManager;
        this.publisher = publisher;
        this.eurekaTransportField = ReflectionUtils.findField(DiscoveryClient.class, "eurekaTransport");
        ReflectionUtils.makeAccessible(this.eurekaTransportField);
    }

父类的构造方法中执行的代码块比较长，一些赋值操作等就忽略了, 这里只摘出比较重要的部分

初始化拉取监控和心跳监控

       if (config.shouldFetchRegistry()) {this.registryStalenessMonitor = new ThresholdLevelsMetric(this, METRIC_REGISTRY_PREFIX + "lastUpdateSec_", new long[]{15L, 30L, 60L, 120L, 240L, 480L});
        } else {this.registryStalenessMonitor = ThresholdLevelsMetric.NO_OP_METRIC;}

        if (config.shouldRegisterWithEureka()) {this.heartbeatStalenessMonitor = new ThresholdLevelsMetric(this, METRIC_REGISTRATION_PREFIX + "lastHeartbeatSec_", new long[]{15L, 30L, 60L, 120L, 240L, 480L});
        } else {this.heartbeatStalenessMonitor = ThresholdLevelsMetric.NO_OP_METRIC;}

当当前实例不需要注册到 EurekaServer 时，构造方法走到这里就结束了


        if (!config.shouldRegisterWithEureka() && !config.shouldFetchRegistry()) {logger.info("Client configured to neither register nor query for data.");
            scheduler = null;
            heartbeatExecutor = null;
            cacheRefreshExecutor = null;
            eurekaTransport = null;
            instanceRegionChecker = new InstanceRegionChecker(new PropertyBasedAzToRegionMapper(config), clientConfig.getRegion());
            DiscoveryManager.getInstance().setDiscoveryClient(this);
            DiscoveryManager.getInstance().setEurekaClientConfig(config);

            initTimestampMs = System.currentTimeMillis();
            logger.info("Discovery Client initialized at timestamp {} with initial instances count: {}",
                    initTimestampMs, this.getApplications().size());

            return;  
        }

初始化心跳线程和刷新线程以及它们的调度器

  try {
            scheduler = Executors.newScheduledThreadPool(2,
                    new ThreadFactoryBuilder()
                            .setNameFormat("DiscoveryClient-%d")
                            .setDaemon(true)
                            .build());

            heartbeatExecutor = new ThreadPoolExecutor(1, clientConfig.getHeartbeatExecutorThreadPoolSize(), 0, TimeUnit.SECONDS,
                    new SynchronousQueue<Runnable>(),
                    new ThreadFactoryBuilder()
                            .setNameFormat("DiscoveryClient-HeartbeatExecutor-%d")
                            .setDaemon(true)
                            .build());  

            cacheRefreshExecutor = new ThreadPoolExecutor(1, clientConfig.getCacheRefreshExecutorThreadPoolSize(), 0, TimeUnit.SECONDS,
                    new SynchronousQueue<Runnable>(),
                    new ThreadFactoryBuilder()
                            .setNameFormat("DiscoveryClient-CacheRefreshExecutor-%d")
                            .setDaemon(true)
                            .build());

从 EurekaServer 拉取注册信息

 if (clientConfig.shouldFetchRegistry() && !fetchRegistry(false)) {fetchRegistryFromBackup();
        }

这里 fetchRegistry 是第一次拉取注册信息，如果拉取不成功的话则执行 fetchRegistryFromBackup 从备份注册中心获取，同样，拉取的信息会放在之后的文章中

注册之前的扩展点

  if (this.preRegistrationHandler != null) {this.preRegistrationHandler.beforeRegistration();
        }

这里是个空的实现，可以通过实现 PreRegistrationHandler 接口做些什么操作

向 EurekaServer 发起注册

 if (clientConfig.shouldRegisterWithEureka() && clientConfig.shouldEnforceRegistrationAtInit()) {
            try {if (!register() ) {throw new IllegalStateException("Registration error at startup. Invalid server response.");
                }
            } catch (Throwable th) {logger.error("Registration error at startup: {}", th.getMessage());
                throw new IllegalStateException(th);
            }
        }

注册方法为register，同样这里先不展开

初始化几个定时任务

initScheduledTasks();

private void initScheduledTasks() {
   // 从 EurekaServer 拉取注册信息
   if (clientConfig.shouldFetchRegistry()) {int registryFetchIntervalSeconds = clientConfig.getRegistryFetchIntervalSeconds();
       int expBackOffBound = clientConfig.getCacheRefreshExecutorExponentialBackOffBound();
       scheduler.schedule(
               new TimedSupervisorTask(
                       "cacheRefresh",
                       scheduler,
                       cacheRefreshExecutor,
                       registryFetchIntervalSeconds,
                       TimeUnit.SECONDS,
                       expBackOffBound,
                       new CacheRefreshThread()),
               registryFetchIntervalSeconds, TimeUnit.SECONDS);
   }

   // 向 EurekaServer 发送续租心跳
   if (clientConfig.shouldRegisterWithEureka()) {int renewalIntervalInSecs = instanceInfo.getLeaseInfo().getRenewalIntervalInSecs();
       int expBackOffBound = clientConfig.getHeartbeatExecutorExponentialBackOffBound();
       logger.info("Starting heartbeat executor:" + "renew interval is:" + renewalIntervalInSecs);

       scheduler.schedule(
               new TimedSupervisorTask(
                       "heartbeat",
                       scheduler,
                       heartbeatExecutor,
                       renewalIntervalInSecs,
                       TimeUnit.SECONDS,
                       expBackOffBound,
                       new HeartbeatThread()),
               renewalIntervalInSecs, TimeUnit.SECONDS);

       instanceInfoReplicator = new InstanceInfoReplicator(
               this,
               instanceInfo,
               clientConfig.getInstanceInfoReplicationIntervalSeconds(),
               2); 

       statusChangeListener = new ApplicationInfoManager.StatusChangeListener() {
           @Override
           public String getId() {return "statusChangeListener";}

           @Override
           public void notify(StatusChangeEvent statusChangeEvent) {if (InstanceStatus.DOWN == statusChangeEvent.getStatus() ||
                       InstanceStatus.DOWN == statusChangeEvent.getPreviousStatus()) {logger.warn("Saw local status change event {}", statusChangeEvent);
               } else {logger.info("Saw local status change event {}", statusChangeEvent);
               }
               instanceInfoReplicator.onDemandUpdate();}
       };

       if (clientConfig.shouldOnDemandUpdateStatusChange()) {
       // 注册状态监听器
           applicationInfoManager.registerStatusChangeListener(statusChangeListener);
       }

       instanceInfoReplicator.start(clientConfig.getInitialInstanceInfoReplicationIntervalSeconds());
   } else {logger.info("Not registering with Eureka server per configuration");
   }
}

至此，EurekaClient 的自动装配与启动流程就解析完毕了

EurekaDiscoveryClientConfiguration

EurekaClientAutoConfiguration

注解

@Import(DiscoveryClientOptionalArgsConfiguration.class)

@ConditionalOnBean(EurekaDiscoveryClientConfiguration.Marker.class)

@AutoConfigureBefore

NoopDiscoveryClientAutoConfiguration

CommonsClientAutoConfiguration

ServiceRegistryAutoConfiguration