EurekaClient自动装配及启动流程解析

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

1. 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
2. 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
3. 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

1. 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

2. 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/syj-study-demo/blob/master/src/main/java/cn/shiyujun/EurekaConfig.md

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

1. 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;
        }

1. 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;
        }

1. 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()
            );

1. 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

1. 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

6. 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

7. 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

本文由博客一文多发平台 OpenWrite 发布！