摘要：于是我們繼續(xù)斷點(diǎn)往下走，發(fā)現(xiàn)對(duì)象里面只有一個(gè)類(lèi)名路徑為。進(jìn)入看看，這個(gè)配置類(lèi)有哪些重要的方法。。。分析一果不其然，方法被調(diào)用了，緊接著也進(jìn)入斷點(diǎn)，然后在往下走，又進(jìn)入的方法中的回調(diào)處。

-

1、鑒于一些朋友的提問(wèn)并提議講解下eureka的源碼分析，由此應(yīng)運(yùn)而產(chǎn)生的本章節(jié)的內(nèi)容；
2、所以我站在自我的理解角度試著整理了這篇Eureka源碼的分析，希望對(duì)大家有所幫助；
3、由于篇幅太長(zhǎng)不能在一篇里面發(fā)布出來(lái)，所以拆分了上下篇；

1、Eureka Server 提供服務(wù)注冊(cè)服務(wù)，各個(gè)節(jié)點(diǎn)啟動(dòng)后，會(huì)在Eureka Server中進(jìn)行注冊(cè)，這樣Eureka Server中的服務(wù)注冊(cè)表中將會(huì)存儲(chǔ)所有可用服務(wù)節(jié)點(diǎn)的信息，服務(wù)節(jié)點(diǎn)的信息可以在界面中直觀的看到。
2、Eureka Client 是一個(gè)Java 客戶(hù)端，用于簡(jiǎn)化與Eureka Server的交互，客戶(hù)端同時(shí)也具備一個(gè)內(nèi)置的、使用輪詢(xún)負(fù)載算法的負(fù)載均衡器。
3、在應(yīng)用啟動(dòng)后，將會(huì)向Eureka Server發(fā)送心跳(默認(rèn)周期為30秒)，如果Eureka Server在多個(gè)心跳周期沒(méi)有收到某個(gè)節(jié)點(diǎn)的心跳，Eureka Server 將會(huì)從服務(wù)注冊(cè)表中把這個(gè)服務(wù)節(jié)點(diǎn)移除(默認(rèn)90秒)。
4、Eureka Server之間將會(huì)通過(guò)復(fù)制的方式完成數(shù)據(jù)的同步；
5、Eureka Client具有緩存的機(jī)制，即使所有的Eureka Server 都掛掉的話(huà)，客戶(hù)端依然可以利用緩存中的信息消費(fèi)其它服務(wù)的API；

詳見(jiàn) SpringCloud（第 049 篇）Netflix Eureka 源碼深入剖析（上）

詳見(jiàn) SpringCloud（第 049 篇）Netflix Eureka 源碼深入剖析（上）

2017-10-23 19:43:07.688  INFO 1488 --- [           main] o.s.c.support.DefaultLifecycleProcessor  : Starting beans in phase 0
2017-10-23 19:43:07.694  INFO 1488 --- [           main] o.s.c.n.eureka.InstanceInfoFactory       : Setting initial instance status as: STARTING
2017-10-23 19:43:07.874  INFO 1488 --- [           main] c.n.d.provider.DiscoveryJerseyProvider   : Using JSON encoding codec LegacyJacksonJson
2017-10-23 19:43:07.874  INFO 1488 --- [           main] c.n.d.provider.DiscoveryJerseyProvider   : Using JSON decoding codec LegacyJacksonJson
2017-10-23 19:43:07.971  INFO 1488 --- [           main] c.n.d.provider.DiscoveryJerseyProvider   : Using XML encoding codec XStreamXml
2017-10-23 19:43:07.971  INFO 1488 --- [           main] c.n.d.provider.DiscoveryJerseyProvider   : Using XML decoding codec XStreamXml
2017-10-23 19:43:08.134  INFO 1488 --- [           main] c.n.d.s.r.aws.ConfigClusterResolver      : Resolving eureka endpoints via configuration
2017-10-23 19:43:08.344  INFO 1488 --- [           main] com.netflix.discovery.DiscoveryClient    : Disable delta property : false
2017-10-23 19:43:08.344  INFO 1488 --- [           main] com.netflix.discovery.DiscoveryClient    : Single vip registry refresh property : null
2017-10-23 19:43:08.344  INFO 1488 --- [           main] com.netflix.discovery.DiscoveryClient    : Force full registry fetch : false
2017-10-23 19:43:08.344  INFO 1488 --- [           main] com.netflix.discovery.DiscoveryClient    : Application is null : false
2017-10-23 19:43:08.344  INFO 1488 --- [           main] com.netflix.discovery.DiscoveryClient    : Registered Applications size is zero : true
2017-10-23 19:43:08.344  INFO 1488 --- [           main] com.netflix.discovery.DiscoveryClient    : Application version is -1: true
2017-10-23 19:43:08.345  INFO 1488 --- [           main] com.netflix.discovery.DiscoveryClient    : Getting all instance registry info from the eureka server
2017-10-23 19:43:08.630  INFO 1488 --- [           main] com.netflix.discovery.DiscoveryClient    : The response status is 200
2017-10-23 19:43:08.631  INFO 1488 --- [           main] com.netflix.discovery.DiscoveryClient    : Starting heartbeat executor: renew interval is: 30
2017-10-23 19:43:08.634  INFO 1488 --- [           main] c.n.discovery.InstanceInfoReplicator     : InstanceInfoReplicator onDemand update allowed rate per min is 4
2017-10-23 19:43:08.637  INFO 1488 --- [           main] com.netflix.discovery.DiscoveryClient    : Discovery Client initialized at timestamp 1508758988637 with initial instances count: 0
2017-10-23 19:43:08.657  INFO 1488 --- [           main] c.n.e.EurekaDiscoveryClientConfiguration : Registering application springms-provider-user with eureka with status UP
2017-10-23 19:43:08.658  INFO 1488 --- [           main] com.netflix.discovery.DiscoveryClient    : Saw local status change event StatusChangeEvent [timestamp=1508758988658, current=UP, previous=STARTING]
2017-10-23 19:43:08.659  INFO 1488 --- [nfoReplicator-0] com.netflix.discovery.DiscoveryClient    : DiscoveryClient_SPRINGMS-PROVIDER-USER/springms-provider-user:192.168.3.101:7900: registering service...
2017-10-23 19:43:08.768  INFO 1488 --- [           main] s.b.c.e.t.TomcatEmbeddedServletContainer : Tomcat started on port(s): 7900 (http)
2017-10-23 19:43:08.768  INFO 1488 --- [           main] c.n.e.EurekaDiscoveryClientConfiguration : Updating port to 7900
2017-10-23 19:43:08.773  INFO 1488 --- [           main] c.s.cloud.MsProviderUserApplication      : Started MsProviderUserApplication in 9.694 seconds (JVM running for 10.398)
【【【【【【 用戶(hù)微服務(wù) 】】】】】】已啟動(dòng).

【分析一】：根據(jù)日志粗粒度看，大多數(shù)日志都是在 DiscoveryClient 打印出來(lái)的，由此我們先不妨將這些打印日志的地方都打上斷點(diǎn)，為了后序
斷點(diǎn)查看調(diào)用堆棧信息。

【分析二】：仔細(xì)查看下日志，先是 DefaultLifecycleProcessor 類(lèi)處理了一些 bean,然后接下來(lái)肯定會(huì)調(diào)用一些實(shí)現(xiàn) SmartLifecycle 類(lèi)的
 start 方法；

【分析三】： 接著初始化設(shè)置了EurekaClient的狀態(tài)為 STARTING，初始化編碼使用的格式，哪些用JSON，哪些用XML；

【分析四】： 緊接著打印了強(qiáng)制獲取注冊(cè)信息狀態(tài)為false，已注冊(cè)的應(yīng)用大小為0，客戶(hù)端發(fā)送心跳續(xù)約，心跳續(xù)約間隔為30秒，最后打印Client
初始化完成；

【分析五】：帶著這些通過(guò)日志查看出來(lái)的端倪，然后我們還得吸取分析EurekaServer的教訓(xùn)，我們得先去 @EnableEurekaClient 注解瞧瞧。

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@EnableDiscoveryClient
public @interface EnableEurekaClient {

}

【分析一】：我們會(huì)發(fā)現(xiàn)，@EnableEurekaClient 注解類(lèi)竟然也使用了注解 @EnableDiscoveryClient，那么我們有必要去這個(gè)注解類(lèi)看看。

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@Import(EnableDiscoveryClientImportSelector.class)
public @interface EnableDiscoveryClient {

}

【分析二】：我們看到的是 @EnableDiscoveryClient 注解類(lèi)有個(gè)比較特殊的注解 @Import，由此我們猜想，這里的大多數(shù)邏輯是不是都寫(xiě)在這個(gè) EnableDiscoveryClientImportSelector 類(lèi)呢？

@Order(Ordered.LOWEST_PRECEDENCE - 100)
public class EnableDiscoveryClientImportSelector
        extends SpringFactoryImportSelector {

    @Override
    protected boolean isEnabled() {
        return new RelaxedPropertyResolver(getEnvironment()).getProperty(
                "spring.cloud.discovery.enabled", Boolean.class, Boolean.TRUE);
    }

    @Override
    protected boolean hasDefaultFactory() {
        return true;
    }

}

【分析一】：EnableDiscoveryClientImportSelector 類(lèi)集成了 SpringFactoryImportSelector 類(lèi)，但是重寫(xiě)了一個(gè) isEnabled() 方
法，默認(rèn)值返回 true，為什么會(huì)返回true，也得有個(gè)說(shuō)法吧，于是我們進(jìn)入父類(lèi) EnableDiscoveryClientImportSelector 看看。

/**
 * Select and return the names of which class(es) should be imported based on
 * the {@link AnnotationMetadata} of the importing @{@link Configuration} class.
 */
@Override
public String[] selectImports(AnnotationMetadata metadata) {
    if (!isEnabled()) { // 打上斷點(diǎn)
        return new String[0];
    }
    AnnotationAttributes attributes = AnnotationAttributes.fromMap(
            metadata.getAnnotationAttributes(this.annotationClass.getName(), true));

    Assert.notNull(attributes, "No " + getSimpleName() + " attributes found. Is "
            + metadata.getClassName() + " annotated with @" + getSimpleName() + "?");

    // Find all possible auto configuration classes, filtering duplicates
    List factories = new ArrayList<>(new LinkedHashSet<>(SpringFactoriesLoader
            .loadFactoryNames(this.annotationClass, this.beanClassLoader)));

    if (factories.isEmpty() && !hasDefaultFactory()) {
        throw new IllegalStateException("Annotation @" + getSimpleName()
                + " found, but there are no implementations. Did you forget to include a starter?");
    }

    if (factories.size() > 1) {
        // there should only ever be one DiscoveryClient, but there might be more than
        // one factory
        log.warn("More than one implementation " + "of @" + getSimpleName()
                + " (now relying on @Conditionals to pick one): " + factories);
    }

    return factories.toArray(new String[factories.size()]);
}

【分析二】：發(fā)現(xiàn)父類(lèi)有這么一個(gè) selectImports 方法使用了 isEnabled() 方法，這個(gè)方法干了些啥事情呢？我們細(xì)看下 selectImports 方法上面的英文注釋?zhuān)笾乱馑际牵哼x擇并且返回需要導(dǎo)入經(jīng)過(guò)注解配置的類(lèi)，由此我們猜想這個(gè)導(dǎo)入的類(lèi)肯定對(duì)我們此次客戶(hù)端分析有莫大的幫助，于
是我們現(xiàn)在這個(gè)方法打上斷點(diǎn)先。于是我們現(xiàn)在該干的事情也干了，沒(méi)有頭緒的時(shí)候，我們現(xiàn)在才Run運(yùn)行EurekaServer，Debug運(yùn)行springms-provider-user。

【分析一】：既然進(jìn)了斷點(diǎn)，我們看看這個(gè)方法，首先通過(guò)注解獲取了一些屬性，然后加載了一些類(lèi)名稱(chēng)，于是我們進(jìn)入 loadFactoryNames 方法看看。

public static List loadFactoryNames(Class factoryClass, ClassLoader classLoader) {
    String factoryClassName = factoryClass.getName();
    try {
        // 注釋?zhuān)簆ublic static final String FACTORIES_RESOURCE_LOCATION = "META-INF/spring.factories";
        // 注釋?zhuān)哼@個(gè) jar 包下的一個(gè)配置文件
        Enumeration urls = (classLoader != null ? classLoader.getResources(FACTORIES_RESOURCE_LOCATION) :
                ClassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION));
        List result = new ArrayList();
        while (urls.hasMoreElements()) {
            URL url = urls.nextElement();
            Properties properties = PropertiesLoaderUtils.loadProperties(new UrlResource(url));
            String factoryClassNames = properties.getProperty(factoryClassName);
            result.addAll(Arrays.asList(StringUtils.commaDelimitedListToStringArray(factoryClassNames)));
        }
        return result;
    }
    catch (IOException ex) {
        throw new IllegalArgumentException("Unable to load [" + factoryClass.getName() +
                "] factories from location [" + FACTORIES_RESOURCE_LOCATION + "]", ex);
    }
}

【分析二】：加載了一個(gè)配置文件，配置文件里面寫(xiě)了啥呢？打開(kāi)SpringFactoryImportSelector該文件所在的jar包的spring.factories文件一看。

# AutoConfiguration
org.springframework.boot.autoconfigure.EnableAutoConfiguration=
org.springframework.cloud.client.CommonsClientAutoConfiguration,
org.springframework.cloud.client.discovery.noop.NoopDiscoveryClientAutoConfiguration,
org.springframework.cloud.client.hypermedia.CloudHypermediaAutoConfiguration,
org.springframework.cloud.client.loadbalancer.LoadBalancerAutoConfiguration,
org.springframework.cloud.commons.util.UtilAutoConfiguration


# Environment Post Processors
org.springframework.boot.env.EnvironmentPostProcessor=
org.springframework.cloud.client.HostInfoEnvironmentPostProcessor

【分析三】：看名稱(chēng)，都是一些 Configuration 后綴的類(lèi)名，所以這些都是加載的一堆堆的配置文件類(lèi)。于是我們繼續(xù)斷點(diǎn)往下走，發(fā)現(xiàn) 
factories 對(duì)象里面只有一個(gè)類(lèi)名路徑為 org.springframework.cloud.netflix.eureka.EurekaDiscoveryClientConfiguration ?？催@個(gè)
名字就應(yīng)該知道這是我們分析EurekaClient的一個(gè)重要的配置類(lèi)，先不管三七二十一，找到該類(lèi)先。

@Configuration
@EnableConfigurationProperties
@ConditionalOnClass(EurekaClientConfig.class)
@ConditionalOnProperty(value = "eureka.client.enabled", matchIfMissing = true)
@CommonsLog
public class EurekaDiscoveryClientConfiguration implements SmartLifecycle, Ordered {

    @Override
    public void start() {
        // only set the port if the nonSecurePort is 0 and this.port != 0
        if (this.port.get() != 0 && this.instanceConfig.getNonSecurePort() == 0) {
            this.instanceConfig.setNonSecurePort(this.port.get());
        }

        // only initialize if nonSecurePort is greater than 0 and it isn"t already running
        // because of containerPortInitializer below
        if (!this.running.get() && this.instanceConfig.getNonSecurePort() > 0) {

            maybeInitializeClient();

            if (log.isInfoEnabled()) {
                log.info("Registering application " + this.instanceConfig.getAppname()
                        + " with eureka with status "
                        + this.instanceConfig.getInitialStatus());
            }

            this.applicationInfoManager
                    .setInstanceStatus(this.instanceConfig.getInitialStatus());

            if (this.healthCheckHandler != null) {
                this.eurekaClient.registerHealthCheck(this.healthCheckHandler);
            }
            this.context.publishEvent(
                    new InstanceRegisteredEvent<>(this, this.instanceConfig));
            this.running.set(true);
        }
    }

    。。。 其它省略了
｝

【分析一】：進(jìn)入這個(gè)類(lèi)，首先看到該類(lèi)實(shí)現(xiàn)了 SmartLifecycle 接口，那么就肯定會(huì)實(shí)現(xiàn) start 方法，而且這個(gè) start 方法感覺(jué)應(yīng)在 “步驟5.1之分析二” 會(huì)被加載執(zhí)行的。

【分析二】：因?yàn)?start 這段代碼不多，所以我就索性將 start 方法中的每段代碼都點(diǎn)進(jìn)去看了看，發(fā)現(xiàn) this.applicationInfoManager.setInstanceStatus(this.instanceConfig.getInitialStatus()) 這段代碼有一個(gè)觀察者模式的回調(diào)存在。

// ApplicationInfoManager.setInstanceStatus 的方法
public synchronized void setInstanceStatus(InstanceStatus status) {// 打上斷點(diǎn)
    InstanceStatus prev = instanceInfo.setStatus(status);
    if (prev != null) {
        for (StatusChangeListener listener : listeners.values()) {
            try {
                listener.notify(new StatusChangeEvent(prev, status));
            } catch (Exception e) {
                logger.warn("failed to notify listener: {}", listener.getId(), e);
            }
        }
    }
}

【分析三】：這個(gè)方法會(huì)因?yàn)闋顟B(tài)的改變而回調(diào)所有實(shí)現(xiàn) StatusChangeListener 這個(gè)類(lèi)的地方，前提得先注冊(cè)到 listeners 中去才行。

【分析四】：于是乎，我們斷定，若想要回調(diào)，那么就必須有地方先注冊(cè)這個(gè)事件，而且這個(gè)注冊(cè)還必須提前執(zhí)行在 start 方法前執(zhí)行，于是我們得先
在 ApplicationInfoManager 這個(gè)類(lèi)中找到注冊(cè)到 listeners 的這個(gè)方法。

public void registerStatusChangeListener(StatusChangeListener listener) {// 打上斷點(diǎn)
    listeners.put(listener.getId(), listener);
}

【分析五】：沒(méi)錯(cuò)，就是這個(gè)方法，肯定有地方調(diào)用這個(gè)方法，不然的話(huà)，那調(diào)用 setInstanceStatus 這個(gè)方法的意義就什么用了。于是我們逆向找
下 registerStatusChangeListener 被調(diào)用的地方。

【分析六】：很不巧的是，盡然只有1個(gè)地方被調(diào)用，這個(gè)地方就是 DiscoveryClient.initScheduledTasks 方法，而且 initScheduledTasks 
方法又是在 DiscoveryClient 的構(gòu)造函數(shù)里面調(diào)用的，同時(shí)我們也對(duì) initScheduledTasks 以及 initScheduledTasks 被調(diào)用的構(gòu)造方法地方
打上斷點(diǎn)。

【分析一】：果不其然，EurekaDiscoveryClientConfiguration.start 方法被調(diào)用了，緊接著 this.applicationInfoManager.setInstanceStatus(this.instanceConfig.getInitialStatus()) 也進(jìn)入斷點(diǎn)，然后在往下走，又進(jìn)入的 
DiscoveryClient.initScheduledTasks 方法中的 notify 回調(diào)處。

【分析二】：看著斷點(diǎn)依次經(jīng)過(guò)我們上述分析的地方，然后也符合日志打印的順序，所以我們現(xiàn)在應(yīng)該是有必要好好看看 DiscoveryClient.initScheduledTasks 這個(gè)方法究竟干了什么偉大的事情。然而又想了想，還不如看看 initScheduledTasks 被調(diào)用的構(gòu)造方法。

@Inject
DiscoveryClient(ApplicationInfoManager applicationInfoManager, EurekaClientConfig config, DiscoveryClientOptionalArgs args, Provider backupRegistryProvider) {
    if (args != null) {
        this.healthCheckHandlerProvider = args.healthCheckHandlerProvider;
        this.healthCheckCallbackProvider = args.healthCheckCallbackProvider;
        this.eventListeners.addAll(args.getEventListeners());
    } else {
        this.healthCheckCallbackProvider = null;
        this.healthCheckHandlerProvider = null;
    }
    
    this.applicationInfoManager = applicationInfoManager;
    InstanceInfo myInfo = applicationInfoManager.getInfo();

    clientConfig = config;
    staticClientConfig = clientConfig;
    transportConfig = config.getTransportConfig();
    instanceInfo = myInfo;
    if (myInfo != null) {
        appPathIdentifier = instanceInfo.getAppName() + "/" + instanceInfo.getId();
    } else {
        logger.warn("Setting instanceInfo to a passed in null value");
    }

    this.backupRegistryProvider = backupRegistryProvider;

    this.urlRandomizer = new EndpointUtils.InstanceInfoBasedUrlRandomizer(instanceInfo);
    localRegionApps.set(new Applications());

    fetchRegistryGeneration = new AtomicLong(0);

    remoteRegionsToFetch = new AtomicReference(clientConfig.fetchRegistryForRemoteRegions());
    remoteRegionsRef = new AtomicReference<>(remoteRegionsToFetch.get() == null ? null : remoteRegionsToFetch.get().split(","));

    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;
    }

    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());

        // This is a bit of hack to allow for existing code using DiscoveryManager.getInstance()
        // to work with DI"d DiscoveryClient
        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;  // no need to setup up an network tasks and we are done
    }

    try {
        // 注釋?zhuān)憾〞r(shí)任務(wù)調(diào)度準(zhǔn)備
        scheduler = Executors.newScheduledThreadPool(3,
                new ThreadFactoryBuilder()
                        .setNameFormat("DiscoveryClient-%d")
                        .setDaemon(true)
                        .build());

        // 注釋?zhuān)簩?shí)例化心跳定時(shí)任務(wù)線(xiàn)程池
        heartbeatExecutor = new ThreadPoolExecutor(
                1, clientConfig.getHeartbeatExecutorThreadPoolSize(), 0, TimeUnit.SECONDS,
                new SynchronousQueue(),
                new ThreadFactoryBuilder()
                        .setNameFormat("DiscoveryClient-HeartbeatExecutor-%d")
                        .setDaemon(true)
                        .build()
        );  // use direct handoff

        // 注釋?zhuān)簩?shí)例化緩存刷新定時(shí)任務(wù)線(xiàn)程池
        cacheRefreshExecutor = new ThreadPoolExecutor(
                1, clientConfig.getCacheRefreshExecutorThreadPoolSize(), 0, TimeUnit.SECONDS,
                new SynchronousQueue(),
                new ThreadFactoryBuilder()
                        .setNameFormat("DiscoveryClient-CacheRefreshExecutor-%d")
                        .setDaemon(true)
                        .build()
        );  // use direct handoff

        eurekaTransport = new EurekaTransport();
        scheduleServerEndpointTask(eurekaTransport, args);

        AzToRegionMapper azToRegionMapper;
        if (clientConfig.shouldUseDnsForFetchingServiceUrls()) {
            azToRegionMapper = new DNSBasedAzToRegionMapper(clientConfig);
        } else {
            azToRegionMapper = new PropertyBasedAzToRegionMapper(clientConfig);
        }
        if (null != remoteRegionsToFetch.get()) {
            azToRegionMapper.setRegionsToFetch(remoteRegionsToFetch.get().split(","));
        }
        instanceRegionChecker = new InstanceRegionChecker(azToRegionMapper, clientConfig.getRegion());
    } catch (Throwable e) {
        throw new RuntimeException("Failed to initialize DiscoveryClient!", e);
    }

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

    // 注釋?zhuān)撼跏蓟{(diào)度任務(wù)
    initScheduledTasks();
    try {
        Monitors.registerObject(this);
    } catch (Throwable e) {
        logger.warn("Cannot register timers", e);
    }

    // This is a bit of hack to allow for existing code using DiscoveryManager.getInstance()
    // to work with DI"d DiscoveryClient
    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());
}

【分析一】：從往下看，initScheduledTasks 這個(gè)方法顧名思義就是初始化調(diào)度任務(wù)，所以這里面的內(nèi)容應(yīng)該就是重頭戲，進(jìn)入看看。

private void initScheduledTasks() {
    if (clientConfig.shouldFetchRegistry()) {
        // registry cache refresh timer
        // 注釋?zhuān)洪g隔多久去拉取服務(wù)注冊(cè)信息，默認(rèn)時(shí)間 30秒
        int registryFetchIntervalSeconds = clientConfig.getRegistryFetchIntervalSeconds();
        int expBackOffBound = clientConfig.getCacheRefreshExecutorExponentialBackOffBound();
        // 注釋?zhuān)憾〞r(shí)任務(wù)，每間隔 30秒 去拉取一次服務(wù)注冊(cè)信息
        scheduler.schedule(
                new TimedSupervisorTask(
                        "cacheRefresh",
                        scheduler,
                        cacheRefreshExecutor,
                        registryFetchIntervalSeconds,
                        TimeUnit.SECONDS,
                        expBackOffBound,
                        new CacheRefreshThread()
                ),
                registryFetchIntervalSeconds, TimeUnit.SECONDS);
    }

    if (clientConfig.shouldRegisterWithEureka()) {
        // 注釋?zhuān)洪g隔多久發(fā)送一次心跳續(xù)約，默認(rèn)間隔時(shí)間 30 秒
        int renewalIntervalInSecs = instanceInfo.getLeaseInfo().getRenewalIntervalInSecs();
        int expBackOffBound = clientConfig.getHeartbeatExecutorExponentialBackOffBound();
        logger.info("Starting heartbeat executor: " + "renew interval is: " + renewalIntervalInSecs);

        // Heartbeat timer
        // 注釋?zhuān)憾〞r(shí)任務(wù)，每間隔 30秒 去想 EurekaServer 發(fā)送一次心跳續(xù)約
        scheduler.schedule(
                new TimedSupervisorTask(
                        "heartbeat",
                        scheduler,
                        heartbeatExecutor,
                        renewalIntervalInSecs,
                        TimeUnit.SECONDS,
                        expBackOffBound,
                        new HeartbeatThread()
                ),
                renewalIntervalInSecs, TimeUnit.SECONDS);

        // InstanceInfo replicator
        // 注釋?zhuān)簩?shí)例信息復(fù)制器，定時(shí)刷新dataCenterInfo數(shù)據(jù)中心信息，默認(rèn)30秒
        instanceInfoReplicator = new InstanceInfoReplicator(
                this,
                instanceInfo,
                clientConfig.getInstanceInfoReplicationIntervalSeconds(),
                2); // burstSize

        // 注釋?zhuān)簩?shí)例化狀態(tài)變化監(jiān)聽(tīng)器
        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()) {
                    // log at warn level if DOWN was involved
                    logger.warn("Saw local status change event {}", statusChangeEvent);
                } else {
                    logger.info("Saw local status change event {}", statusChangeEvent);
                }

                // 注釋?zhuān)籂顟B(tài)有變化的話(huà)，會(huì)回調(diào)這個(gè)方法
                instanceInfoReplicator.onDemandUpdate();
            }
        };

        // 注釋?zhuān)鹤?cè)狀態(tài)變化監(jiān)聽(tīng)器
        if (clientConfig.shouldOnDemandUpdateStatusChange()) {
            applicationInfoManager.registerStatusChangeListener(statusChangeListener);
        }

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

【分析二】：在這個(gè)方法從上往下一路注釋分析下來(lái)，干了EurekaClient我們最想知道的一些事情，定時(shí)任務(wù)獲取注冊(cè)信息，定時(shí)任務(wù)刷新緩存，定時(shí)
任務(wù)心跳續(xù)約，定時(shí)任務(wù)同步數(shù)據(jù)中心數(shù)據(jù)，狀態(tài)變化監(jiān)聽(tīng)回調(diào)等。但是唯獨(dú)沒(méi)看到注冊(cè)，這是怎么回事呢？

【分析三】：我們忘記了一個(gè)重要的方法，instanceInfoReplicator.onDemandUpdate() 就是在狀態(tài)改變的時(shí)候，我們是如何處理的？由此，我們覺(jué)得這里面肯定有貓膩，不然沒(méi)辦法注冊(cè)呀。

public boolean onDemandUpdate() {
    if (rateLimiter.acquire(burstSize, allowedRatePerMinute)) {
        scheduler.submit(new Runnable() {
            @Override
            public void run() {
                logger.debug("Executing on-demand update of local InstanceInfo");

                Future latestPeriodic = scheduledPeriodicRef.get();
                if (latestPeriodic != null && !latestPeriodic.isDone()) {
                    logger.debug("Canceling the latest scheduled update, it will be rescheduled at the end of on demand update");
                    latestPeriodic.cancel(false);
                }

                // 注釋?zhuān)哼@里進(jìn)行了實(shí)例信息刷新和注冊(cè)
                InstanceInfoReplicator.this.run();
            }
        });
        return true;
    } else {
        logger.warn("Ignoring onDemand update due to rate limiter");
        return false;
    }
}

【分析四】：onDemandUpdate 這個(gè)方法，看來(lái)看去，唯獨(dú) InstanceInfoReplicator.this.run() 這個(gè)方法還有點(diǎn)用，而且還是 run 方法呢，感情 InstanceInfoReplicator 這個(gè)類(lèi)還是實(shí)現(xiàn)了 Runnable 接口？經(jīng)過(guò)查看這個(gè)類(lèi)，還真是實(shí)現(xiàn)了 Runnable 接口。

【分析五】：于是乎，我們有理由相信，這個(gè)方法應(yīng)該我們要找的注冊(cè)所在的地方，翻開(kāi)代碼看看究竟。

public void run() {
    try {
        discoveryClient.refreshInstanceInfo();

        Long dirtyTimestamp = instanceInfo.isDirtyWithTime();
        if (dirtyTimestamp != null) {
            discoveryClient.register();
            instanceInfo.unsetIsDirty(dirtyTimestamp);
        }
    } catch (Throwable t) {
        logger.warn("There was a problem with the instance info replicator", t);
    } finally {
        Future next = scheduler.schedule(this, replicationIntervalSeconds, TimeUnit.SECONDS);
        scheduledPeriodicRef.set(next);
    }
}

【分析六】：映入眼簾的就是 discoveryClient.register() 這個(gè)刺眼的 register 方法，終于有點(diǎn)苗頭了，原來(lái)注冊(cè)方法找的這么千辛萬(wàn)苦。雖然找到了這里，但是我還是想看看這個(gè)讓我們找的千辛萬(wàn)苦的注冊(cè)方法到底是怎么注冊(cè)的呢？

boolean register() throws Throwable {
    logger.info(PREFIX + appPathIdentifier + ": registering service...");
    EurekaHttpResponse httpResponse;
    try {
        httpResponse = eurekaTransport.registrationClient.register(instanceInfo);
    } catch (Exception e) {
        logger.warn("{} - registration failed {}", PREFIX + appPathIdentifier, e.getMessage(), e);
        throw e;
    }
    if (logger.isInfoEnabled()) {
        logger.info("{} - registration status: {}", PREFIX + appPathIdentifier, httpResponse.getStatusCode());
    }
    return httpResponse.getStatusCode() == 204;
}

【分析七】：原來(lái)調(diào)用了 EurekaHttpClient 封裝的客戶(hù)端請(qǐng)求對(duì)象來(lái)進(jìn)行注冊(cè)的，再繼續(xù)深探 registrationClient.register 方法，于是我們來(lái)到了 AbstractJerseyEurekaHttpClient.register 方法。

@Override
public EurekaHttpResponse register(InstanceInfo info) {
    String urlPath = "apps/" + info.getAppName();
    ClientResponse response = null;
    try {
        Builder resourceBuilder = jerseyClient.resource(serviceUrl).path(urlPath).getRequestBuilder();
        addExtraHeaders(resourceBuilder);
        response = resourceBuilder
                .header("Accept-Encoding", "gzip")
                .type(MediaType.APPLICATION_JSON_TYPE)
                .accept(MediaType.APPLICATION_JSON)
                // 注釋?zhuān)捍虬鼛袭?dāng)前應(yīng)用的所有信息 info
                .post(ClientResponse.class, info);
        return anEurekaHttpResponse(response.getStatus()).headers(headersOf(response)).build();
    } finally {
        if (logger.isDebugEnabled()) {
            logger.debug("Jersey HTTP POST {}/{} with instance {}; statusCode={}", serviceUrl, urlPath, info.getId(),
                    response == null ? "N/A" : response.getStatus());
        }
        if (response != null) {
            response.close();
        }
    }
}

【分析八】：原來(lái)調(diào)用的是 Jersey RESTful 框架來(lái)進(jìn)行請(qǐng)求的，然后在 EurekaServer 那邊就會(huì)在 ApplicationResource.addInstance 方法接收客戶(hù)端的注冊(cè)請(qǐng)求，因此我們的 EurekaClient 是如何注冊(cè)的就到此為止了。

【分析九】：至于那些續(xù)約、心跳的流程分析和這個(gè)注冊(cè)的流程大體差不多，相信大家按照我剛剛這么分析斷點(diǎn)下去，一定能分析的很到位的。

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