DiscoveryClient 核心方法解析
1）服務註冊（發送註冊請求到註冊中心）
boolean register() throws Throwable {
...
EurekaHttpResponse<Void> httpResponse;
try {
//主要的註冊功能 實現在AbstractJerseyEurekaHttpClient.register()
httpResponse = eurekaTransport.registrationClient.register(instanceInfo);
}
...
return httpResponse.getStatusCode() == 204;
}
//AbstractJerseyEurekaHttpClient.register()
public EurekaHttpResponse<Void> register(InstanceInfo info) {
String urlPath = "apps/" + info.getAppName();
ClientResponse response = null;
EurekaHttpResponse var5;
try {
// 1.構造一個HTTP請求
Builder resourceBuilder = jerseyClient.resource(serviceUrl).path(urlPath).getRequestBuilder();
addExtraHeaders(resourceBuilder);
// 2.封裝請求類型和返回類型，將當前服務的元信息封裝爲InstanceInfo，
// 發送post請求到serviceUrl，serviceUrl即我們在配置文件中配置的defaultZone
response = resourceBuilder
.header("Accept-Encoding", "gzip")
.type(MediaType.APPLICATION_JSON_TYPE)
.accept(MediaType.APPLICATION_JSON)
.post(ClientResponse.class, info);
// 3.返回響應狀態
var5 = EurekaHttpResponse.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();
}
}
return var5;
}
2）服務續約（本質就是發送當前應用的心跳請求到註冊中心）
boolean renew() {
try {
// 1.本質就是發送心跳請求
// 2.真正實現爲 AbstractJerseyEurekaHttpClient.sendHeartBeat()
EurekaHttpResponse<InstanceInfo> httpResponse = this.eurekaTransport.registrationClient.sendHeartBeat(this.instanceInfo.getAppName(), this.instanceInfo.getId(), this.instanceInfo, (InstanceStatus)null);
logger.debug("DiscoveryClient_{} - Heartbeat status: {}", this.appPathIdentifier, httpResponse.getStatusCode());
// 2.如果請求失敗，則調用註冊服務請求
if (httpResponse.getStatusCode() == 404) {
this.REREGISTER_COUNTER.increment();
logger.info("DiscoveryClient_{} - Re-registering apps/{}", this.appPathIdentifier, this.instanceInfo.getAppName());
long timestamp = this.instanceInfo.setIsDirtyWithTime();
boolean success = this.register();
if (success) {
this.instanceInfo.unsetIsDirty(timestamp);
}
return success;
} else {
return httpResponse.getStatusCode() == 200;
}
} catch (Throwable var5) {
logger.error("DiscoveryClient_{} - was unable to send heartbeat!", this.appPathIdentifier, var5);
return false;
}
}
// AbstractJerseyEurekaHttpClient.sendHeartBeat()
public EurekaHttpResponse<InstanceInfo> sendHeartBeat(String appName, String id, InstanceInfo info, InstanceStatus overriddenStatus) {
String urlPath = "apps/" + appName + '/' + id;
ClientResponse response = null;
EurekaHttpResponse var10;
try {
// 主要就是將當前實例的元信息（InstanceInfo）以及狀態（UP）通過HTTP請求發送到serviceUrl
WebResource webResource = this.jerseyClient.resource(this.serviceUrl).path(urlPath).queryParam("status", info.getStatus().toString()).queryParam("lastDirtyTimestamp", info.getLastDirtyTimestamp().toString());
if (overriddenStatus != null) {
webResource = webResource.queryParam("overriddenstatus", overriddenStatus.name());
}
Builder requestBuilder = webResource.getRequestBuilder();
this.addExtraHeaders(requestBuilder);
response = (ClientResponse)requestBuilder.put(ClientResponse.class);
EurekaHttpResponseBuilder<InstanceInfo> eurekaResponseBuilder = EurekaHttpResponse.anEurekaHttpResponse(response.getStatus(), InstanceInfo.class).headers(headersOf(response));
if (response.hasEntity()) {
eurekaResponseBuilder.entity(response.getEntity(InstanceInfo.class));
}
var10 = eurekaResponseBuilder.build();
} finally {
if (logger.isDebugEnabled()) {
logger.debug("Jersey HTTP PUT {}/{}; statusCode={}", new Object[]{this.serviceUrl, urlPath, response == null ? "N/A" : response.getStatus()});
}
if (response != null) {
response.close();
}
}
return var10;
}
3）服務調用（本質就是獲取調用服務名所對應的服務提供者實例信息，包括IP、port等）
public List<InstanceInfo> getInstancesByVipAddress(String vipAddress, boolean secure) {
return this.getInstancesByVipAddress(vipAddress, secure, this.instanceRegionChecker.getLocalRegion());
}
public List<InstanceInfo> getInstancesByVipAddress(String vipAddress, boolean secure, @Nullable String region) {
if (vipAddress == null) {
throw new IllegalArgumentException("Supplied VIP Address cannot be null");
} else {
Applications applications;
// 1.判斷服務提供方是否當前region，若是的話直接從localRegionApps中獲取
if (this.instanceRegionChecker.isLocalRegion(region)) {
applications = (Applications)this.localRegionApps.get();
} else {
// 2.否則的話從遠程region獲取
applications = (Applications)this.remoteRegionVsApps.get(region);
if (null == applications) {
logger.debug("No applications are defined for region {}, so returning an empty instance list for vip address {}.", region, vipAddress);
return Collections.emptyList();
}
}
// 3.從applications中獲取服務名稱對應的實例名稱列表
return !secure ? applications.getInstancesByVirtualHostName(vipAddress) : applications.getInstancesBySecureVirtualHostName(vipAddress);
}
}
4）服務下線（本質就是發送取消註冊的HTTP請求到註冊中心）
void unregister() {
if (this.eurekaTransport != null && this.eurekaTransport.registrationClient != null) {
try {
logger.info("Unregistering ...");
EurekaHttpResponse<Void> httpResponse = this.eurekaTransport.registrationClient.cancel(this.instanceInfo.getAppName(), this.instanceInfo.getId());
logger.info("DiscoveryClient_{} - deregister status: {}", this.appPathIdentifier, httpResponse.getStatusCode());
} catch (Exception var2) {
logger.error("DiscoveryClient_{} - de-registration failed{}", new Object[]{this.appPathIdentifier, var2.getMessage(), var2});
}
}
}
// AbstractJerseyEurekaHttpClient.cancel()
public EurekaHttpResponse<Void> cancel(String appName, String id) {
String urlPath = "apps/" + appName + '/' + id;
ClientResponse response = null;
EurekaHttpResponse var6;
try {
Builder resourceBuilder = this.jerseyClient.resource(this.serviceUrl).path(urlPath).getRequestBuilder();
this.addExtraHeaders(resourceBuilder);
// 本質就是發送delete請求到註冊中心
response = (ClientResponse)resourceBuilder.delete(ClientResponse.class);
var6 = EurekaHttpResponse.anEurekaHttpResponse(response.getStatus()).headers(headersOf(response)).build();
} finally {
if (logger.isDebugEnabled()) {
logger.debug("Jersey HTTP DELETE {}/{}; statusCode={}", new Object[]{this.serviceUrl, urlPath, response == null ? "N/A" : response.getStatus()});
}
if (response != null) {
response.close();
}
}
return var6;
}
通過以上分析可知，服務的註冊、下線等操作實際上就是通過發送HTTP請求到註冊中心來實現的。那麼這些操作的執行時機是什麼時候呢？是什麼時候服務註冊操作會被調用？下線操作是如何被觸發的？我們還是來看com.netflix.discovery.DiscoveryClient這個類，這個類在應用啓動的時候被加載到容器中，肯定會調用其構造方法，
DiscoveryClient 構造方法解析
@Inject
DiscoveryClient(ApplicationInfoManager applicationInfoManager, EurekaClientConfig config, AbstractDiscoveryClientOptionalArgs args,
Provider<BackupRegistry> backupRegistryProvider) {
// 一系列的參數配置
...
try {
// 下面是幾個線程池的創建
scheduler = Executors.newScheduledThreadPool(3,
new ThreadFactoryBuilder()
.setNameFormat("DiscoveryClient-%d")
.setDaemon(true)
.build());
// 心跳線程池（維持當前應用續約的線程池，用來持續發送心跳請求）
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()
);
...
// 核心方法調用 啓動定時任務
initScheduledTasks();
try {
Monitors.registerObject(this);
} catch (Throwable e) {
logger.warn("Cannot register timers", e);
}
...
}
//initScheduledTasks()
private void initScheduledTasks() {
if (clientConfig.shouldFetchRegistry()) {
// registry cache refresh timer
int registryFetchIntervalSeconds = clientConfig.getRegistryFetchIntervalSeconds();
int expBackOffBound = clientConfig.getCacheRefreshExecutorExponentialBackOffBound();
// 1.執行刷新任務的定時器
scheduler.schedule(
new TimedSupervisorTask(
"cacheRefresh",
scheduler,
cacheRefreshExecutor,
registryFetchIntervalSeconds,
TimeUnit.SECONDS,
expBackOffBound,
//線程任務在這裏，主要就是爲了執行這個Thread的run()
new CacheRefreshThread()
),
registryFetchIntervalSeconds, TimeUnit.SECONDS);
}
// 2.客戶端默認註冊到eureka，shouldRegisterWithEureka()默認爲true
if (clientConfig.shouldRegisterWithEureka()) {
int renewalIntervalInSecs = instanceInfo.getLeaseInfo().getRenewalIntervalInSecs();
int expBackOffBound = clientConfig.getHeartbeatExecutorExponentialBackOffBound();
logger.info("Starting heartbeat executor: " + "renew interval is: " + renewalIntervalInSecs);
// 3.執行心跳任務的定時器
scheduler.schedule(
new TimedSupervisorTask(
"heartbeat",
scheduler,
heartbeatExecutor,
renewalIntervalInSecs,
TimeUnit.SECONDS,
expBackOffBound,
// 主要就是執行該Thread的run()
new HeartbeatThread()
),
renewalIntervalInSecs, TimeUnit.SECONDS);
// 獲取當前註冊服務的基本信息
instanceInfoReplicator = new InstanceInfoReplicator(
this,
instanceInfo,
clientConfig.getInstanceInfoReplicationIntervalSeconds(),
2);
...
// 4.將當前服務註冊到註冊中心
instanceInfoReplicator.start(clientConfig.getInitialInstanceInfoReplicationIntervalSeconds());
} else {
logger.info("Not registering with Eureka server per configuration");
}
}
1）CacheRefreshThread執行刷新任務的線程
class CacheRefreshThread implements Runnable {
public void run() {
refreshRegistry();
}
}
@VisibleForTesting
void refreshRegistry() {
try {
...
// 獲取註冊信息，客戶端定時去刷新服務信息
boolean success = fetchRegistry(remoteRegionsModified);
if (success) {
registrySize = localRegionApps.get().size();
lastSuccessfulRegistryFetchTimestamp = System.currentTimeMillis();
}
...
} catch (Throwable e) {
logger.error("Cannot fetch registry from server", e);
}
}
private boolean fetchRegistry(boolean forceFullRegistryFetch) {
Stopwatch tracer = this.FETCH_REGISTRY_TIMER.start();
label122: {
boolean var4;
try {
Applications applications = this.getApplications();
if (!this.clientConfig.shouldDisableDelta() && Strings.isNullOrEmpty(this.clientConfig.getRegistryRefreshSingleVipAddress()) && !forceFullRegistryFetch && applications != null && applications.getRegisteredApplications().size() != 0 && applications.getVersion() != -1L) {
this.getAndUpdateDelta(applications);
} else {
logger.info("Disable delta property : {}", this.clientConfig.shouldDisableDelta());
logger.info("Single vip registry refresh property : {}", this.clientConfig.getRegistryRefreshSingleVipAddress());
logger.info("Force full registry fetch : {}", forceFullRegistryFetch);
logger.info("Application is null : {}", applications == null);
logger.info("Registered Applications size is zero : {}", applications.getRegisteredApplications().size() == 0);
logger.info("Application version is -1: {}", applications.getVersion() == -1L);
this.getAndStoreFullRegistry();
}
applications.setAppsHashCode(applications.getReconcileHashCode());
this.logTotalInstances();
break label122;
} catch (Throwable var8) {
logger.error("DiscoveryClient_{} - was unable to refresh its cache! status = {}", new Object[]{this.appPathIdentifier, var8.getMessage(), var8});
var4 = false;
} finally {
if (tracer != null) {
tracer.stop();
}
}
return var4;
}
this.onCacheRefreshed();
this.updateInstanceRemoteStatus();
return true;
}
2）HeartbeatThread執行心跳續約任務的線程
private class HeartbeatThread implements Runnable {
private HeartbeatThread() {
}
public void run() {
//最終調用renew()續約
if (DiscoveryClient.this.renew()) {
DiscoveryClient.this.lastSuccessfulHeartbeatTimestamp = System.currentTimeMillis();
}
}
}
3）this.instanceInfoReplicator.start(this.clientConfig.getInitialInstanceInfoReplicationIntervalSeconds()); 發送註冊請求到註冊中心
public void start(int initialDelayMs) {
if (this.started.compareAndSet(false, true)) {
this.instanceInfo.setIsDirty();
// 啓動一個定時任務，任務指向this，
// class InstanceInfoReplicator implements Runnable ，由該類可知，真正執行的是其run()方法
Future next = this.scheduler.schedule(this, (long)initialDelayMs, TimeUnit.SECONDS);
this.scheduledPeriodicRef.set(next);
}
}
public void run() {
boolean var6 = false;
ScheduledFuture next;
label53: {
try {
var6 = true;
this.discoveryClient.refreshInstanceInfo();
Long dirtyTimestamp = this.instanceInfo.isDirtyWithTime();
if (dirtyTimestamp != null) {
// 真正的註冊實現在這裏，參考上篇問章可知，這裏也是發送一個HTTP請求到註冊中心
this.discoveryClient.register();
this.instanceInfo.unsetIsDirty(dirtyTimestamp);
var6 = false;
} else {
var6 = false;
}
break label53;
} catch (Throwable var7) {
logger.warn("There was a problem with the instance info replicator", var7);
var6 = false;
} finally {
if (var6) {
ScheduledFuture next = this.scheduler.schedule(this, (long)this.replicationIntervalSeconds, TimeUnit.SECONDS);
this.scheduledPeriodicRef.set(next);
}
}
next = this.scheduler.schedule(this, (long)this.replicationIntervalSeconds, TimeUnit.SECONDS);
this.scheduledPeriodicRef.set(next);
return;
}
next = this.scheduler.schedule(this, (long)this.replicationIntervalSeconds, TimeUnit.SECONDS);
this.scheduledPeriodicRef.set(next);
}
綜上分析可知，在項目啓動的時候通過@EnableDiscoveryClient最終實例化DiscoveryClient實例，在其構造方法中，啓動了三個線程池， 並且分別啓動了三個定時任務：
a、註冊當前服務到註冊中心；
b、持續發送心跳進行續約任務；
c、定時刷新註冊中心註冊細信息到本地