這次我們說(shuō)一下eureka的全量獲取。EurekaClient 啟動(dòng)時(shí)，首先執(zhí)行一次全量獲取進(jìn)行本地緩存注冊(cè)信息。

localRegionApps.set(new Applications());
if (clientConfig.shouldFetchRegistry() && !fetchRegistry(false)) {
        fetchRegistryFromBackup();
    }

配置 eureka.shouldFetchRegistry = true，開(kāi)啟從 EurekaServer獲取注冊(cè)信息泳梆。默認(rèn)值：true。
調(diào)用 fetchRegistry(false)方法榜掌，從 Eureka-Server 全量獲取注冊(cè)信息优妙。
EurekaClient在初始化過(guò)程中，創(chuàng)建獲取注冊(cè)信息線程憎账，固定間隔向 Eureka-Server 發(fā)起獲取注冊(cè)信息( fetch )套硼，刷新本地注冊(cè)信息緩存

private void initScheduledTasks() {
    // 從 Eureka-Server 拉取注冊(cè)信息執(zhí)行器
    if (clientConfig.shouldFetchRegistry()) {
        // registry cache refresh timer
        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 Eureka-Server 心跳（續(xù)租）執(zhí)行器
    if (clientConfig.shouldRegisterWithEureka()) {
        int renewalIntervalInSecs = instanceInfo.getLeaseInfo().getRenewalIntervalInSecs(); // 續(xù)租頻率
        int expBackOffBound = clientConfig.getHeartbeatExecutorExponentialBackOffBound(); // 系數(shù)
        logger.info("Starting heartbeat executor: " + "renew interval is: " + renewalIntervalInSecs);

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

        // 創(chuàng)建 應(yīng)用實(shí)例信息復(fù)制器
        // InstanceInfo replicator
        instanceInfoReplicator = new InstanceInfoReplicator(
                this,
                instanceInfo,
                clientConfig.getInstanceInfoReplicationIntervalSeconds(),
                2); // burstSize

        // 創(chuàng)建 應(yīng)用實(shí)例狀態(tài)變更監(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);
                }
                instanceInfoReplicator.onDemandUpdate();
            }
        };

        // 注冊(cè) 應(yīng)用實(shí)例狀態(tài)變更監(jiān)聽(tīng)器
        if (clientConfig.shouldOnDemandUpdateStatusChange()) {
            applicationInfoManager.registerStatusChangeListener(statusChangeListener);
        }

        // 開(kāi)啟 應(yīng)用實(shí)例信息復(fù)制器
        instanceInfoReplicator.start(clientConfig.getInitialInstanceInfoReplicationIntervalSeconds());
    } else {
        logger.info("Not registering with Eureka server per configuration");
    }
}

調(diào)用 refreshRegistry(false)方法，刷新注冊(cè)信息緩存

void refreshRegistry() {
    try {
        boolean isFetchingRemoteRegionRegistries = isFetchingRemoteRegionRegistries();

        boolean remoteRegionsModified = false;
        // This makes sure that a dynamic change to remote regions to fetch is honored.
        String latestRemoteRegions = clientConfig.fetchRegistryForRemoteRegions();
        if (null != latestRemoteRegions) {
            String currentRemoteRegions = remoteRegionsToFetch.get();
            if (!latestRemoteRegions.equals(currentRemoteRegions)) {
                // Both remoteRegionsToFetch and AzToRegionMapper.regionsToFetch need to be in sync
                synchronized (instanceRegionChecker.getAzToRegionMapper()) {
                    if (remoteRegionsToFetch.compareAndSet(currentRemoteRegions, latestRemoteRegions)) {
                        String[] remoteRegions = latestRemoteRegions.split(",");
                        remoteRegionsRef.set(remoteRegions);
                        instanceRegionChecker.getAzToRegionMapper().setRegionsToFetch(remoteRegions);
                        remoteRegionsModified = true;
                    } else {
                        logger.info("Remote regions to fetch modified concurrently," +
                                " ignoring change from {} to {}", currentRemoteRegions, latestRemoteRegions);
                    }
                }
            } else {
                // Just refresh mapping to reflect any DNS/Property change
                instanceRegionChecker.getAzToRegionMapper().refreshMapping();
            }
        }

        boolean success = fetchRegistry(remoteRegionsModified);
        if (success) {
            // 設(shè)置 注冊(cè)信息的應(yīng)用實(shí)例數(shù)
            registrySize = localRegionApps.get().size();
            // 設(shè)置 最后獲取注冊(cè)信息時(shí)間
            lastSuccessfulRegistryFetchTimestamp = System.currentTimeMillis();
        }


        if (logger.isDebugEnabled()) {
            StringBuilder allAppsHashCodes = new StringBuilder();
            allAppsHashCodes.append("Local region apps hashcode: ");
            allAppsHashCodes.append(localRegionApps.get().getAppsHashCode());
            allAppsHashCodes.append(", is fetching remote regions? ");
            allAppsHashCodes.append(isFetchingRemoteRegionRegistries);
            for (Map.Entry<String, Applications> entry : remoteRegionVsApps.entrySet()) {
                allAppsHashCodes.append(", Remote region: ");
                allAppsHashCodes.append(entry.getKey());
                allAppsHashCodes.append(" , apps hashcode: ");
                allAppsHashCodes.append(entry.getValue().getAppsHashCode());
            }
            logger.debug("Completed cache refresh task for discovery. All Apps hash code is {} ",
                    allAppsHashCodes.toString());
        }
    } catch (Throwable e) {
        logger.error("Cannot fetch registry from server", e);
    }        
}

調(diào)用 fetchRegistry方法胞皱，從EurekaServer獲取注冊(cè)信息

private boolean fetchRegistry(boolean forceFullRegistryFetch) {
    Stopwatch tracer = FETCH_REGISTRY_TIMER.start();

    try {
        // 獲取 本地緩存的注冊(cè)的應(yīng)用實(shí)例集合
        // If the delta is disabled or if it is the first time, get all
        // applications
        Applications applications = getApplications();

        // 全量獲取
        if (clientConfig.shouldDisableDelta() // 禁用增量獲取
                || (!Strings.isNullOrEmpty(clientConfig.getRegistryRefreshSingleVipAddress()))
                || forceFullRegistryFetch
                || (applications == null) // 空
                || (applications.getRegisteredApplications().size() == 0) // 空
                || (applications.getVersion() == -1)) //Client application does not have latest library supporting delta
        {
            logger.info("Disable delta property : {}", clientConfig.shouldDisableDelta());
            logger.info("Single vip registry refresh property : {}", 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() == -1));
            // 執(zhí)行 全量獲取
            getAndStoreFullRegistry();
        } else {
            // 執(zhí)行 增量獲取
            getAndUpdateDelta(applications);
        }
        // 設(shè)置 應(yīng)用集合 hashcode
        applications.setAppsHashCode(applications.getReconcileHashCode());
        // 打印 本地緩存的注冊(cè)的應(yīng)用實(shí)例數(shù)量
        logTotalInstances();
    } catch (Throwable e) {
        logger.error(PREFIX + appPathIdentifier + " - was unable to refresh its cache! status = " + e.getMessage(), e);
        return false;
    } finally {
        if (tracer != null) {
            tracer.stop();
        }
    }

    // Notify about cache refresh before updating the instance remote status
    onCacheRefreshed();

    // Update remote status based on refreshed data held in the cache
    updateInstanceRemoteStatus();

    // registry was fetched successfully, so return true
    return true;
}

調(diào)用 getAndStoreFullRegistry方法邪意，全量獲取注冊(cè)信息，并設(shè)置到本地緩存

private void getAndStoreFullRegistry() throws Throwable {
    long currentUpdateGeneration = fetchRegistryGeneration.get();

    logger.info("Getting all instance registry info from the eureka server");

    // 全量獲取注冊(cè)信息
    Applications apps = null;
    EurekaHttpResponse<Applications> httpResponse = clientConfig.getRegistryRefreshSingleVipAddress() == null
            ? eurekaTransport.queryClient.getApplications(remoteRegionsRef.get())
            : eurekaTransport.queryClient.getVip(clientConfig.getRegistryRefreshSingleVipAddress(), remoteRegionsRef.get());
    if (httpResponse.getStatusCode() == Status.OK.getStatusCode()) {
        apps = httpResponse.getEntity();
    }
    logger.info("The response status is {}", httpResponse.getStatusCode());

    // 設(shè)置到本地緩存
    if (apps == null) {
        logger.error("The application is null for some reason. Not storing this information");
    } else if (fetchRegistryGeneration.compareAndSet(currentUpdateGeneration, currentUpdateGeneration + 1)) {
        localRegionApps.set(this.filterAndShuffle(apps));
        logger.debug("Got full registry with apps hashcode {}", apps.getAppsHashCode());
    } else {
        logger.warn("Not updating applications as another thread is updating it already");
    }
}

ApplicationsResource反砌，處理所有應(yīng)用的請(qǐng)求操作的 Resource ( Controller )抄罕。

接收全量獲取請(qǐng)求，映射 getContainers方法

@GET
public Response getContainers(@PathParam("version") String version,
                              @HeaderParam(HEADER_ACCEPT) String acceptHeader,
                              @HeaderParam(HEADER_ACCEPT_ENCODING) String acceptEncoding,
                              @HeaderParam(EurekaAccept.HTTP_X_EUREKA_ACCEPT) String eurekaAccept,
                              @Context UriInfo uriInfo,
                              @Nullable @QueryParam("regions") String regionsStr) {
    // TODO[0009]：RemoteRegionRegistry
    boolean isRemoteRegionRequested = null != regionsStr && !regionsStr.isEmpty();
    String[] regions = null;
    if (!isRemoteRegionRequested) {
        EurekaMonitors.GET_ALL.increment();
    } else {
        regions = regionsStr.toLowerCase().split(",");
        Arrays.sort(regions); // So we don't have different caches for same regions queried in different order.
        EurekaMonitors.GET_ALL_WITH_REMOTE_REGIONS.increment();
    }

    // 判斷是否可以訪問(wèn)
    // Check if the server allows the access to the registry. The server can
    // restrict access if it is not
    // ready to serve traffic depending on various reasons.
    if (!registry.shouldAllowAccess(isRemoteRegionRequested)) {
        return Response.status(Status.FORBIDDEN).build();
    }

    // API 版本
    CurrentRequestVersion.set(Version.toEnum(version));

    // 返回?cái)?shù)據(jù)格式
    KeyType keyType = Key.KeyType.JSON;
    String returnMediaType = MediaType.APPLICATION_JSON;
    if (acceptHeader == null || !acceptHeader.contains(HEADER_JSON_VALUE)) {
        keyType = Key.KeyType.XML;
        returnMediaType = MediaType.APPLICATION_XML;
    }

    // 響應(yīng)緩存鍵( KEY )
    Key cacheKey = new Key(Key.EntityType.Application,
            ResponseCacheImpl.ALL_APPS,
            keyType, CurrentRequestVersion.get(), EurekaAccept.fromString(eurekaAccept), regions
    );

    // 響應(yīng)緩存結(jié)果
    Response response;
    if (acceptEncoding != null && acceptEncoding.contains(HEADER_GZIP_VALUE)) {
        response = Response.ok(responseCache.getGZIP(cacheKey))
                .header(HEADER_CONTENT_ENCODING, HEADER_GZIP_VALUE)
                .header(HEADER_CONTENT_TYPE, returnMediaType)
                .build();
    } else {
        response = Response.ok(responseCache.get(cacheKey))
                .build();
    }
    return response;
}

ResponseCacheImpl于颖，響應(yīng)緩存實(shí)現(xiàn)類。

在 ResponseCacheImpl 里嚷兔，將緩存拆分成兩層 ：

只讀緩存( readOnlyCacheMap )
固定過(guò)期 + 固定大小的讀寫緩存( readWriteCacheMap )

緩存過(guò)期策略如下：

應(yīng)用實(shí)例注冊(cè)森渐、下線做入、過(guò)期時(shí)，只過(guò)期 readWriteCacheMap 同衣。
readWriteCacheMap 寫入一段時(shí)間( 可配置 )后自動(dòng)過(guò)期竟块。
定時(shí)任務(wù)對(duì)比 readWriteCacheMap 和 readOnlyCacheMap 的緩存值，若不一致耐齐，以前者為主浪秘。通過(guò)這樣的方式，實(shí)現(xiàn)了 readOnlyCacheMap 的定時(shí)過(guò)期埠况。
調(diào)用ResponseCacheImpl的get方法耸携，獲取緩存

String get(final Key key, boolean useReadOnlyCache) {
    Value payload = getValue(key, useReadOnlyCache);
    if (payload == null || payload.getPayload().equals(EMPTY_PAYLOAD)) {
        return null;
    } else {
        return payload.getPayload();
    }
}

調(diào)用 AbstractInstanceRegistry的getApplications方法，獲取注冊(cè)的應(yīng)用集合

public Applications getApplications() {
    boolean disableTransparentFallback = serverConfig.disableTransparentFallbackToOtherRegion();
    if (disableTransparentFallback) { // TODO[0009]：RemoteRegionRegistry
        return getApplicationsFromLocalRegionOnly();
    } else {
        return getApplicationsFromAllRemoteRegions();  // Behavior of falling back to remote region can be disabled.
    }
}

定時(shí)任務(wù)對(duì)比 readWriteCacheMap 和 readOnlyCacheMap 的緩存值辕翰，若不一致夺衍，以前者為主。通過(guò)這樣的方式喜命，實(shí)現(xiàn)了 readOnlyCacheMap 的定時(shí)過(guò)期沟沙。

private TimerTask getCacheUpdateTask() {
    return new TimerTask() {
        @Override
        public void run() {
            logger.debug("Updating the client cache from response cache");
            for (Key key : readOnlyCacheMap.keySet()) { // 循環(huán) readOnlyCacheMap 的緩存鍵
                if (logger.isDebugEnabled()) {
                    Object[] args = {key.getEntityType(), key.getName(), key.getVersion(), key.getType()};
                    logger.debug("Updating the client cache from response cache for key : {} {} {} {}", args);
                }
                try {
                    CurrentRequestVersion.set(key.getVersion());
                    Value cacheValue = readWriteCacheMap.get(key);
                    Value currentCacheValue = readOnlyCacheMap.get(key);
                    if (cacheValue != currentCacheValue) { // 不一致時(shí)，進(jìn)行替換
                        readOnlyCacheMap.put(key, cacheValue);
                    }
                } catch (Throwable th) {
                    logger.error("Error while updating the client cache from response cache for key {}", key.toStringCompact(), th);
                }
            }
        }
    };
}

eureka的全量獲取就完成了壁榕。