SpringCloud注册中心Eureka源码分析（三）

SpringCloud注册中心Eureka源码分析

服务注册
在理解了多个注册中心信息的加载后，我们再回头看看DiscoveryClient类是如何实现“服务注册”行为的，通过查看它的构造类，可以找到它调用了下面这个函数：

private void initScheduledTasks() {
        int renewalIntervalInSecs;
        int expBackOffBound;
        if (this.clientConfig.shouldFetchRegistry()) {
            renewalIntervalInSecs = this.clientConfig.getRegistryFetchIntervalSeconds();
            expBackOffBound = this.clientConfig.getCacheRefreshExecutorExponentialBackOffBound();
            this.scheduler.schedule(new TimedSupervisorTask("cacheRefresh", this.scheduler, this.cacheRefreshExecutor, renewalIntervalInSecs, TimeUnit.SECONDS, expBackOffBound, new DiscoveryClient.CacheRefreshThread()), (long)renewalIntervalInSecs, TimeUnit.SECONDS);
        }

        if (this.clientConfig.shouldRegisterWithEureka()) {
            renewalIntervalInSecs = this.instanceInfo.getLeaseInfo().getRenewalIntervalInSecs();
            expBackOffBound = this.clientConfig.getHeartbeatExecutorExponentialBackOffBound();
            logger.info("Starting heartbeat executor: renew interval is: " + renewalIntervalInSecs);
            this.scheduler.schedule(new TimedSupervisorTask("heartbeat", this.scheduler, this.heartbeatExecutor, renewalIntervalInSecs, TimeUnit.SECONDS, expBackOffBound, new DiscoveryClient.HeartbeatThread()), (long)renewalIntervalInSecs, TimeUnit.SECONDS);
            this.instanceInfoReplicator = new InstanceInfoReplicator(this, this.instanceInfo, this.clientConfig.getInstanceInfoReplicationIntervalSeconds(), 2);
            this.statusChangeListener = new StatusChangeListener() {
                public String getId() {
                    return "statusChangeListener";
                }

                public void notify(StatusChangeEvent statusChangeEvent) {
                    if (InstanceStatus.DOWN != statusChangeEvent.getStatus() && InstanceStatus.DOWN != statusChangeEvent.getPreviousStatus()) {
                        DiscoveryClient.logger.info("Saw local status change event {}", statusChangeEvent);
                    } else {
                        DiscoveryClient.logger.warn("Saw local status change event {}", statusChangeEvent);
                    }

                    DiscoveryClient.this.instanceInfoReplicator.onDemandUpdate();
                }
            };
            if (this.clientConfig.shouldOnDemandUpdateStatusChange()) {
                this.applicationInfoManager.registerStatusChangeListener(this.statusChangeListener);
            }

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

    }

从上面的函数中，可以看到一个与服务注册相关的语句if(clientConfig.shouldRegisterWithEureka())。在该分支内，创建了一个InstanceInfoReplicator类的实例，它会执行一个定时任务，而这个定时任务的具体工作可以查看该类的run()函数，具体如下：

public void run() {
        boolean var6 = false;

        ScheduledFuture next;
        label53: {
            try {
                var6 = true;
                this.discoveryClient.refreshInstanceInfo();
                Long dirtyTimestamp = this.instanceInfo.isDirtyWithTime();
                if (dirtyTimestamp != null) {
                    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);
    }

在以上代码中，discoveryClient.register();这一行，真正触发调用注册的地方就在这里。继续查看register()的内容，如下：

boolean register() throws Throwable {
        logger.info("DiscoveryClient_" + this.appPathIdentifier + ": registering service...");

        EurekaHttpResponse httpResponse;
        try {
            httpResponse = this.eurekaTransport.registrationClient.register(this.instanceInfo);
        } catch (Exception var3) {
            logger.warn("{} - registration failed {}", new Object[]{"DiscoveryClient_" + this.appPathIdentifier, var3.getMessage(), var3});
            throw var3;
        }

        if (logger.isInfoEnabled()) {
            logger.info("{} - registration status: {}", "DiscoveryClient_" + this.appPathIdentifier, httpResponse.getStatusCode());
        }

        return httpResponse.getStatusCode() == 204;
    }

注册操作中也是通过Rest请求的方式进行的。同时，我们能看到发起注册请求的时候，传入了一个com.netflix.appinfo.InstanceInfo对象，该对象就是注册客户端给服务器的服务的元数据。