SpringCloud（第 050 篇）Netflix Eureka 源碼深入剖析（下）
一觅够、大致介紹
1、鑒于一些朋友的提問并提議講解下eureka的源碼分析穷缤，由此應(yīng)運(yùn)而產(chǎn)生的本章節(jié)的內(nèi)容惠拭；
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，希望對大家有所幫助焕窝；
3蹬挺、由于篇幅太長不能在一篇里面發(fā)布出來，所以拆分了上下篇它掂；
二巴帮、基本原理
1、Eureka Server 提供服務(wù)注冊服務(wù)虐秋，各個(gè)節(jié)點(diǎn)啟動后榕茧，會在Eureka Server中進(jìn)行注冊，這樣Eureka Server中的服務(wù)注冊表中將會存儲所有可用服務(wù)節(jié)點(diǎn)的信息客给，服務(wù)節(jié)點(diǎn)的信息可以在界面中直觀的看到用押。
2、Eureka Client 是一個(gè)Java 客戶端靶剑，用于簡化與Eureka Server的交互蜻拨，客戶端同時(shí)也具備一個(gè)內(nèi)置的、使用輪詢負(fù)載算法的負(fù)載均衡器桩引。
3缎讼、在應(yīng)用啟動后，將會向Eureka Server發(fā)送心跳(默認(rèn)周期為30秒)坑匠，如果Eureka Server在多個(gè)心跳周期沒有收到某個(gè)節(jié)點(diǎn)的心跳血崭，Eureka Server 將會從服務(wù)注冊表中把這個(gè)服務(wù)節(jié)點(diǎn)移除(默認(rèn)90秒)。
4厘灼、Eureka Server之間將會通過復(fù)制的方式完成數(shù)據(jù)的同步夹纫；
5、Eureka Client具有緩存的機(jī)制设凹，即使所有的Eureka Server 都掛掉的話捷凄，客戶端依然可以利用緩存中的信息消費(fèi)其它服務(wù)的API；
三围来、EurekaServer 啟動流程分析
詳見 SpringCloud（第 049 篇）Netflix Eureka 源碼深入剖析（上）
四跺涤、EurekaServer 處理服務(wù)注冊匈睁、集群數(shù)據(jù)復(fù)制
詳見 SpringCloud（第 049 篇）Netflix Eureka 源碼深入剖析（上）
五、EurekaClient 啟動流程分析
5.1 調(diào)換運(yùn)行模式桶错，Run運(yùn)行 springms-discovery-eureka 服務(wù)航唆，Debug 運(yùn)行 springms-provider-user 服務(wù)，先觀察日志先院刁；
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)
【【【【【【 用戶微服務(wù) 】】】】】】已啟動.
【分析一】：根據(jù)日志粗粒度看糯钙，大多數(shù)日志都是在 DiscoveryClient 打印出來的，由此我們先不妨將這些打印日志的地方都打上斷點(diǎn)退腥，為了后序
斷點(diǎn)查看調(diào)用堆棧信息任岸。
【分析二】：仔細(xì)查看下日志，先是 DefaultLifecycleProcessor 類處理了一些 bean,然后接下來肯定會調(diào)用一些實(shí)現(xiàn) SmartLifecycle 類的
start 方法狡刘；
【分析三】： 接著初始化設(shè)置了EurekaClient的狀態(tài)為 STARTING享潜，初始化編碼使用的格式，哪些用JSON嗅蔬，哪些用XML剑按；
【分析四】： 緊接著打印了強(qiáng)制獲取注冊信息狀態(tài)為false，已注冊的應(yīng)用大小為0澜术，客戶端發(fā)送心跳續(xù)約艺蝴，心跳續(xù)約間隔為30秒，最后打印Client
初始化完成鸟废；
【分析五】：帶著這些通過日志查看出來的端倪猜敢，然后我們還得吸取分析EurekaServer的教訓(xùn)，我們得先去 @EnableEurekaClient 注解瞧瞧盒延。
5.2 有目的性的先去 MsProviderUserApplication 看看锣枝，鏈接點(diǎn)進(jìn) EnableEurekaClient 瞧瞧。
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@EnableDiscoveryClient
public @interface EnableEurekaClient {
}
【分析一】：我們會發(fā)現(xiàn)兰英，@EnableEurekaClient 注解類竟然也使用了注解 @EnableDiscoveryClient撇叁，那么我們有必要去這個(gè)注解類看看。
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@Import(EnableDiscoveryClientImportSelector.class)
public @interface EnableDiscoveryClient {
}
【分析二】：我們看到的是 @EnableDiscoveryClient 注解類有個(gè)比較特殊的注解 @Import畦贸，由此我們猜想陨闹，這里的大多數(shù)邏輯是不是都寫在這個(gè) EnableDiscoveryClientImportSelector 類呢？
5.3 進(jìn)入 EnableDiscoveryClientImportSelector 看看到底做了些啥薄坏？
@Order(Ordered.LOWEST_PRECEDENCE - 100)
public class EnableDiscoveryClientImportSelector
extends SpringFactoryImportSelector<EnableDiscoveryClient> {
@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 類集成了 SpringFactoryImportSelector 類趋厉，但是重寫了一個(gè) isEnabled() 方
法，默認(rèn)值返回 true胶坠，為什么會返回true君账，也得有個(gè)說法吧，于是我們進(jìn)入父類 EnableDiscoveryClientImportSelector 看看沈善。
/**
* 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<String> 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)父類有這么一個(gè) selectImports 方法使用了 isEnabled() 方法乡数，這個(gè)方法干了些啥事情呢椭蹄？我們細(xì)看下 selectImports 方法上面的英文注釋，大致意思是：選擇并且返回需要導(dǎo)入經(jīng)過注解配置的類净赴，由此我們猜想這個(gè)導(dǎo)入的類肯定對我們此次客戶端分析有莫大的幫助绳矩，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玖翅，沒有頭緒的時(shí)候翼馆，我們現(xiàn)在才Run運(yùn)行EurekaServer，Debug運(yùn)行springms-provider-user金度。
5.4 EnableDiscoveryClientImportSelector.selectImports 這個(gè)方法果然進(jìn)斷點(diǎn)了应媚。
【分析一】：既然進(jìn)了斷點(diǎn)，我們看看這個(gè)方法猜极，首先通過注解獲取了一些屬性中姜，然后加載了一些類名稱，于是我們進(jìn)入 loadFactoryNames 方法看看魔吐。
public static List<String> loadFactoryNames(Class<?> factoryClass, ClassLoader classLoader) {
String factoryClassName = factoryClass.getName();
try {
// 注釋：public static final String FACTORIES_RESOURCE_LOCATION = "META-INF/spring.factories";
// 注釋：這個(gè) jar 包下的一個(gè)配置文件
Enumeration<URL> urls = (classLoader != null ? classLoader.getResources(FACTORIES_RESOURCE_LOCATION) :
ClassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION));
List<String> result = new ArrayList<String>();
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)配置文件扎筒，配置文件里面寫了啥呢莱找？打開SpringFactoryImportSelector該文件所在的jar包的spring.factories文件一看酬姆。
# 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，都是一些 Configuration 后綴的類名奥溺，所以這些都是加載的一堆堆的配置文件類辞色。于是我們繼續(xù)斷點(diǎn)往下走，發(fā)現(xiàn)
factories 對象里面只有一個(gè)類名路徑為 org.springframework.cloud.netflix.eureka.EurekaDiscoveryClientConfiguration 浮定∠嗦看這個(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，先不管三七二十一桦卒，找到該類先立美。
5.5 進(jìn)入 EurekaDiscoveryClientConfiguration 看看，這個(gè)配置類有哪些重要的方法方灾？
@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);
}
}
建蹄。。裕偿。 其它省略了
｝
【分析一】：進(jìn)入這個(gè)類洞慎，首先看到該類實(shí)現(xiàn)了 SmartLifecycle 接口，那么就肯定會實(shí)現(xiàn) start 方法嘿棘，而且這個(gè) start 方法感覺應(yīng)在 “步驟5.1之分析二” 會被加載執(zhí)行的劲腿。
【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)去看了看鸟妙，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)存在焦人。
// 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)方法會因?yàn)闋顟B(tài)的改變而回調(diào)所有實(shí)現(xiàn) StatusChangeListener 這個(gè)類的地方挥吵，前提得先注冊到 listeners 中去才行。
【分析四】：于是乎垃瞧，我們斷定蔫劣，若想要回調(diào)，那么就必須有地方先注冊這個(gè)事件个从，而且這個(gè)注冊還必須提前執(zhí)行在 start 方法前執(zhí)行脉幢，于是我們得先
在 ApplicationInfoManager 這個(gè)類中找到注冊到 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】：沒錯(cuò)嗦锐，就是這個(gè)方法嫌松，肯定有地方調(diào)用這個(gè)方法，不然的話奕污，那調(diào)用 setInstanceStatus 這個(gè)方法的意義就什么用了萎羔。于是我們逆向找
下 registerStatusChangeListener 被調(diào)用的地方。
【分析六】：很不巧的是碳默，盡然只有1個(gè)地方被調(diào)用贾陷，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)用的嘱根，同時(shí)我們也對 initScheduledTasks 以及 initScheduledTasks 被調(diào)用的構(gòu)造方法地方
打上斷點(diǎn)髓废。
5.6 由于翻閱代碼時(shí)間有點(diǎn)久了，因此我們關(guān)閉 springms-provider-user 微服務(wù)该抒，重新 Debug 運(yùn)行一下慌洪。
【分析一】：果不其然，EurekaDiscoveryClientConfiguration.start 方法被調(diào)用了凑保，緊接著 this.applicationInfoManager.setInstanceStatus(this.instanceConfig.getInitialStatus()) 也進(jìn)入斷點(diǎn)冈爹，然后在往下走，又進(jìn)入的
DiscoveryClient.initScheduledTasks 方法中的 notify 回調(diào)處欧引。
【分析二】：看著斷點(diǎn)依次經(jīng)過我們上述分析的地方频伤，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芝此。然而又想了想憋肖，還不如看看 initScheduledTasks 被調(diào)用的構(gòu)造方法。
5.7 進(jìn)入 DiscoveryClient 經(jīng)過 @Inject 注解過的構(gòu)造方法癌蓖。
@Inject
DiscoveryClient(ApplicationInfoManager applicationInfoManager, EurekaClientConfig config, DiscoveryClientOptionalArgs args, Provider<BackupRegistry> 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<String>(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：定時(shí)任務(wù)調(diào)度準(zhǔn)備
scheduler = Executors.newScheduledThreadPool(3,
new ThreadFactoryBuilder()
.setNameFormat("DiscoveryClient-%d")
.setDaemon(true)
.build());
// 注釋：實(shí)例化心跳定時(shí)任務(wù)線程池
heartbeatExecutor = new ThreadPoolExecutor(
1, clientConfig.getHeartbeatExecutorThreadPoolSize(), 0, TimeUnit.SECONDS,
new SynchronousQueue<Runnable>(),
new ThreadFactoryBuilder()
.setNameFormat("DiscoveryClient-HeartbeatExecutor-%d")
.setDaemon(true)
.build()
); // use direct handoff
// 注釋：實(shí)例化緩存刷新定時(shí)任務(wù)線程池
cacheRefreshExecutor = new ThreadPoolExecutor(
1, clientConfig.getCacheRefreshExecutorThreadPoolSize(), 0, TimeUnit.SECONDS,
new SynchronousQueue<Runnable>(),
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：初始化調(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】：從往下看瞬哼，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)該就是重頭戲租副，進(jìn)入看看坐慰。
private void initScheduledTasks() {
if (clientConfig.shouldFetchRegistry()) {
// registry cache refresh timer
// 注釋：間隔多久去拉取服務(wù)注冊信息，默認(rèn)時(shí)間 30秒
int registryFetchIntervalSeconds = clientConfig.getRegistryFetchIntervalSeconds();
int expBackOffBound = clientConfig.getCacheRefreshExecutorExponentialBackOffBound();
// 注釋：定時(shí)任務(wù)，每間隔 30秒 去拉取一次服務(wù)注冊信息
scheduler.schedule(
new TimedSupervisorTask(
"cacheRefresh",
scheduler,
cacheRefreshExecutor,
registryFetchIntervalSeconds,
TimeUnit.SECONDS,
expBackOffBound,
new CacheRefreshThread()
),
registryFetchIntervalSeconds, TimeUnit.SECONDS);
}
if (clientConfig.shouldRegisterWithEureka()) {
// 注釋：間隔多久發(fā)送一次心跳續(xù)約结胀，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：定時(shí)任務(wù)赞咙，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：實(shí)例信息復(fù)制器，定時(shí)刷新dataCenterInfo數(shù)據(jù)中心信息糟港，默認(rèn)30秒
instanceInfoReplicator = new InstanceInfoReplicator(
this,
instanceInfo,
clientConfig.getInstanceInfoReplicationIntervalSeconds(),
2); // burstSize
// 注釋：實(shí)例化狀態(tài)變化監(jiān)聽器
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：狀態(tài)有變化的話攀操，會回調(diào)這個(gè)方法
instanceInfoReplicator.onDemandUpdate();
}
};
// 注釋：注冊狀態(tài)變化監(jiān)聽器
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，干了EurekaClient我們最想知道的一些事情秸抚，定時(shí)任務(wù)獲取注冊信息速和，定時(shí)任務(wù)刷新緩存，定時(shí)
任務(wù)心跳續(xù)約剥汤，定時(shí)任務(wù)同步數(shù)據(jù)中心數(shù)據(jù)颠放，狀態(tài)變化監(jiān)聽回調(diào)等。但是唯獨(dú)沒看到注冊吭敢，這是怎么回事呢碰凶？
【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)候鹿驼，我們是如何處理的欲低？由此，我們覺得這里面肯定有貓膩畜晰，不然沒辦法注冊呀砾莱。
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：這里進(jìn)行了實(shí)例信息刷新和注冊
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，看來看去舷蟀，唯獨(dú) InstanceInfoReplicator.this.run() 這個(gè)方法還有點(diǎn)用恤磷，而且還是 run 方法呢面哼，感情 InstanceInfoReplicator 這個(gè)類還是實(shí)現(xiàn)了 Runnable 接口野宜？經(jīng)過查看這個(gè)類，還真是實(shí)現(xiàn)了 Runnable 接口魔策。
【分析五】：于是乎匈子，我們有理由相信，這個(gè)方法應(yīng)該我們要找的注冊所在的地方闯袒，翻開代碼看看究竟虎敦。
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)苗頭了政敢，原來注冊方法找的這么千辛萬苦其徙。雖然找到了這里，但是我還是想看看這個(gè)讓我們找的千辛萬苦的注冊方法到底是怎么注冊的呢喷户？
boolean register() throws Throwable {
logger.info(PREFIX + appPathIdentifier + ": registering service...");
EurekaHttpResponse<Void> 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】：原來調(diào)用了 EurekaHttpClient 封裝的客戶端請求對象來進(jìn)行注冊的唾那，再繼續(xù)深探 registrationClient.register 方法，于是我們來到了 AbstractJerseyEurekaHttpClient.register 方法褪尝。
@Override
public EurekaHttpResponse<Void> 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：打包帶上當(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】：原來調(diào)用的是 Jersey RESTful 框架來進(jìn)行請求的闹获，然后在 EurekaServer 那邊就會在 ApplicationResource.addInstance 方法接收客戶端的注冊請求期犬，因此我們的 EurekaClient 是如何注冊的就到此為止了。
【分析九】：至于那些續(xù)約避诽、心跳的流程分析和這個(gè)注冊的流程大體差不多龟虎，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沙庐。
六鲤妥、下載地址
https://gitee.com/ylimhhmily/SpringCloudTutorial.git
SpringCloudTutorial交流QQ群: 235322432
SpringCloudTutorial交流微信群: 微信溝通群二維碼圖片鏈接
歡迎關(guān)注，您的肯定是對我最大的支持!!!
