1.在SpringBoot项目启动时通过SpringApplication.run方法来启动项目
public class ApolloApplication {
public static void main(String[] args) {
SpringApplication.run(ApolloApplication.class, args);
}
}2.点击run方法并找到run方法的实际执行方法，在run方法种有一个prepareContext方法里实现了获取Apollo配置。
public ConfigurableApplicationContext run(String... args) {
StopWatch stopWatch = new StopWatch();
stopWatch.start();
DefaultBootstrapContext bootstrapContext = createBootstrapContext();
ConfigurableApplicationContext context = null;
configureHeadlessProperty();
SpringApplicationRunListeners listeners = getRunListeners(args);
listeners.starting(bootstrapContext, this.mainApplicationClass);
try {
ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
ConfigurableEnvironment environment = prepareEnvironment(listeners, bootstrapContext, applicationArguments);
configureIgnoreBeanInfo(environment);
Banner printedBanner = printBanner(environment);
context = createApplicationContext();
context.setApplicationStartup(this.applicationStartup);
// 这里调用了Application的初始化方法
prepareContext(bootstrapContext, context, environment, listeners, applicationArguments, printedBanner);
refreshContext(context);
afterRefresh(context, applicationArguments);
stopWatch.stop();
if (this.logStartupInfo) {
new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch);
}
listeners.started(context);
callRunners(context, applicationArguments);
}
catch (Throwable ex) {
handleRunFailure(context, ex, listeners);
throw new IllegalStateException(ex);
}
try {
listeners.running(context);
}
catch (Throwable ex) {
handleRunFailure(context, ex, null);
throw new IllegalStateException(ex);
}
return context;
}我们继续来研究prepareContext方法，点开prepareContext方法，我们发现了 applyInitializers方法。
private void prepareContext(DefaultBootstrapContext bootstrapContext, ConfigurableApplicationContext context,
ConfigurableEnvironment environment, SpringApplicationRunListeners listeners,
ApplicationArguments applicationArguments, Banner printedBanner) {
context.setEnvironment(environment);
postProcessApplicationContext(context);
// 这里调用了Application的初始化方法
applyInitializers(context);
listeners.contextPrepared(context);
bootstrapContext.close(context);
if (this.logStartupInfo) {
logStartupInfo(context.getParent() == null);
logStartupProfileInfo(context);
}
// Add boot specific singleton beans
ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
beanFactory.registerSingleton("springApplicationArguments", applicationArguments);
if (printedBanner != null) {
beanFactory.registerSingleton("springBootBanner", printedBanner);
}
if (beanFactory instanceof DefaultListableBeanFactory) {
((DefaultListableBeanFactory) beanFactory)
.setAllowBeanDefinitionOverriding(this.allowBeanDefinitionOverriding);
}
if (this.lazyInitialization) {
context.addBeanFactoryPostProcessor(new LazyInitializationBeanFactoryPostProcessor());
}
// Load the sources
Set<Object> sources = getAllSources();
Assert.notEmpty(sources, "Sources must not be empty");
load(context, sources.toArray(new Object[0]));
listeners.contextLoaded(context);
}继续深入，我们发现该方法时获取到所有实现了ApplicationContextInitializer对象并执行该对象的
initialize方法。
protected void applyInitializers(ConfigurableApplicationContext context) {
for (ApplicationContextInitializer initializer : getInitializers()) {
Class<?> requiredType = GenericTypeResolver.resolveTypeArgument(initializer.getClass(),
ApplicationContextInitializer.class);
Assert.isInstanceOf(requiredType, context, "Unable to call initializer.");
initializer.initialize(context);
}
}ApplicationContextInitializer 是一个接口，该接口有何作用大家可以上网百度。
在Apollo项目中有一个ApolloApplicationContextInitializer 类实现了ApplicationContextInitializer接口。
public class ApolloApplicationContextInitializer implements
ApplicationContextInitializer<ConfigurableApplicationContext> , EnvironmentPostProcessor, Ordered {
// 省略......
}在该类中我们找到了initialize方法，并找到了根据命名空间获取Apollo配置的方法ConfigService.getConfig
protected void initialize(ConfigurableEnvironment environment) {
if (environment.getPropertySources().contains(PropertySourcesConstants.APOLLO_BOOTSTRAP_PROPERTY_SOURCE_NAME)) {
//already initialized
return;
}
String namespaces = environment.getProperty(PropertySourcesConstants.APOLLO_BOOTSTRAP_NAMESPACES, ConfigConsts.NAMESPACE_APPLICATION);
logger.debug("Apollo bootstrap namespaces: {}", namespaces);
List<String> namespaceList = NAMESPACE_SPLITTER.splitToList(namespaces);
CompositePropertySource composite = new CompositePropertySource(PropertySourcesConstants.APOLLO_BOOTSTRAP_PROPERTY_SOURCE_NAME);
for (String namespace : namespaceList) {
// 此处获取Apollo配置
Config config = ConfigService.getConfig(namespace);
composite.addPropertySource(configPropertySourceFactory.getConfigPropertySource(namespace, config));
}
environment.getPropertySources().addFirst(composite);
}我们继续追踪的脚步找到了ConfigService类下的getConfig方法
public static Config getConfig(String namespace) {
return s_instance.getManager().getConfig(namespace);
}点击getConfig方法我们发现定位到了ConfigMager接口下的getConfig方法，继续点击其实现类定位到了DefaultConfigManager类下的getConfig实现方法并在其中找到了factory.create方法。
public Config getConfig(String namespace) {
Config config = m_configs.get(namespace);
if (config == null) {
synchronized (this) {
config = m_configs.get(namespace);
if (config == null) {
ConfigFactory factory = m_factoryManager.getFactory(namespace);
// 此次获取Apollo配置
config = factory.create(namespace);
m_configs.put(namespace, config);
}
}
}点击create方法我们找到了ConfigFactory接口里的create方法，点击找到其实现类，我们找到了
DefaultConfigFactory里的create方法。
public Config create(String namespace) {
ConfigFileFormat format = determineFileFormat(namespace);
// 读取properties文件
if (ConfigFileFormat.isPropertiesCompatible(format)) {
return new DefaultConfig(namespace, createPropertiesCompatibleFileConfigRepository(namespace, format));
}
// Apollo是远程读取走createLocalConfigRepository方法
return new DefaultConfig(namespace, createLocalConfigRepository(namespace));
}点击createLocalConfigRepository方法跳转到该类下该方法
LocalFileConfigRepository createLocalConfigRepository(String namespace) {
if (m_configUtil.isInLocalMode()) {
logger.warn(
"==== Apollo is in local mode! Won't pull configs from remote server for namespace {} ! ====",
namespace);
return new LocalFileConfigRepository(namespace);
}
// createRemoteConfigRepository加载Apollo配置
return new LocalFileConfigRepository(namespace, createRemoteConfigRepository(namespace));
}继续定位createRemoteConfigRepository方法
RemoteConfigRepository createRemoteConfigRepository(String namespace) {
// 该方法加载Apollo配置
return new RemoteConfigRepository(namespace);
}在RemoteConfigRepository类的构造方法：
public RemoteConfigRepository(String namespace) {
m_namespace = namespace; // config名称
m_configCache = new AtomicReference<>();// config引用
m_configUtil = ApolloInjector.getInstance(ConfigUtil.class);// 单例的 config 配置,存放 application.properties
m_httpUtil = ApolloInjector.getInstance(HttpUtil.class);// http工具
m_serviceLocator = ApolloInjector.getInstance(ConfigServiceLocator.class);// 远程服务url更新类
remoteConfigLongPollService = ApolloInjector.getInstance(RemoteConfigLongPollService.class);// 长轮询服务
m_longPollServiceDto = new AtomicReference<>();// 长轮询发现的当前配置发生变化的服务
m_remoteMessages = new AtomicReference<>();
m_loadConfigRateLimiter = RateLimiter.create(m_configUtil.getLoadConfigQPS());// 限流器
m_configNeedForceRefresh = new AtomicBoolean(true);// 是否强制刷新
m_loadConfigFailSchedulePolicy = new ExponentialSchedulePolicy(m_configUtil.getOnErrorRetryInterval(),
m_configUtil.getOnErrorRetryInterval() * 8);// 1 * 8;失败定时重试策略: 最小一秒,最大 8 秒.
gson = new Gson();// json 序列化
gson = new Gson();
this.trySync();// 第一次同步
this.schedulePeriodicRefresh();// 定时刷新
this.scheduleLongPollin// 长轮询刷新在该构造方法中有三个方法比较重要
this.trySync();// 第一次同步，获取Apollo配置
this.schedulePeriodicRefresh();// 定时刷新
this.scheduleLongPollin// 长轮询刷新，获取Apollo配置
方法一和方法三都回去通过HTTP请求获取Apollo配置一共获取两次。
方法二：定时任务主要由一个线程 的线程池维护这定时任务，每五分钟执行一次。
方法一：通过trySync定位到AbstractConfigRepository接口里的sync方法，找到AbstractConfigRepository接口里的sync方法后可以定位到RemoteConfigRepository（远程配置仓库类）类里的sync实现方法，并定位到该方法里的loadApolloConfig方法。
protected boolean trySync() {
try {
// 获取Apollo配置
sync();
return true;
} catch (Throwable ex) {
Tracer.logEvent("ApolloConfigException", ExceptionUtil.getDetailMessage(ex));
logger
.warn("Sync config failed, will retry. Repository {}, reason: {}", this.getClass(), ExceptionUtil
.getDetailMessage(ex));
}
return false;
}@Override
protected synchronized void sync() {
Transaction transaction = Tracer.newTransaction("Apollo.ConfigService", "syncRemoteConfig");
try {
ApolloConfig previous = m_configCache.get();
// 获取Apollo配置
ApolloConfig current = loadApolloConfig();
//reference equals means HTTP 304
if (previous != current) {
logger.debug("Remote Config refreshed!");
m_configCache.set(current);
this.fireRepositoryChange(m_namespace, this.getConfig());
}
if (current != null) {
Tracer.logEvent(String.format("Apollo.Client.Configs.%s", current.getNamespaceName()),
current.getReleaseKey());
}
transaction.setStatus(Transaction.SUCCESS);
} catch (Throwable ex) {
transaction.setStatus(ex);
throw ex;
} finally {
transaction.complete();
}
}点击loadApolloConfig方法，我们发现了发送HTTP请求到Apollo获取配置的内容。
private ApolloConfig loadApolloConfig() {
if (!m_loadConfigRateLimiter.tryAcquire(5, TimeUnit.SECONDS)) {
//wait at most 5 seconds
try {
TimeUnit.SECONDS.sleep(5);
} catch (InterruptedException e) {
}
}
String appId = m_configUtil.getAppId();
String cluster = m_configUtil.getCluster();
String dataCenter = m_configUtil.getDataCenter();
Tracer.logEvent("Apollo.Client.ConfigMeta", STRING_JOINER.join(appId, cluster, m_namespace));
int maxRetries = m_configNeedForceRefresh.get() ? 2 : 1;
long onErrorSleepTime = 0; // 0 means no sleep
Throwable exception = null;
List<ServiceDTO> configServices = getConfigServices();
String url = null;
for (int i = 0; i < maxRetries; i++) {
List<ServiceDTO> randomConfigServices = Lists.newLinkedList(configServices);
Collections.shuffle(randomConfigServices);
//Access the server which notifies the client first
if (m_longPollServiceDto.get() != null) {
randomConfigServices.add(0, m_longPollServiceDto.getAndSet(null));
}
for (ServiceDTO configService : randomConfigServices) {
if (onErrorSleepTime > 0) {
logger.warn(
"Load config failed, will retry in {} {}. appId: {}, cluster: {}, namespaces: {}",
onErrorSleepTime, m_configUtil.getOnErrorRetryIntervalTimeUnit(), appId, cluster, m_namespace);
try {
m_configUtil.getOnErrorRetryIntervalTimeUnit().sleep(onErrorSleepTime);
} catch (InterruptedException e) {
//ignore
}
}
url = assembleQueryConfigUrl(configService.getHomepageUrl(), appId, cluster, m_namespace,
dataCenter, m_remoteMessages.get(), m_configCache.get());
logger.debug("Loading config from {}", url);
HttpRequest request = new HttpRequest(url);
Transaction transaction = Tracer.newTransaction("Apollo.ConfigService", "queryConfig");
transaction.addData("Url", url);
try {
HttpResponse<ApolloConfig> response = m_httpUtil.doGet(request, ApolloConfig.class);
m_configNeedForceRefresh.set(false);
m_loadConfigFailSchedulePolicy.success();
transaction.addData("StatusCode", response.getStatusCode());
transaction.setStatus(Transaction.SUCCESS);
if (response.getStatusCode() == 304) {
logger.debug("Config server responds with 304 HTTP status code.");
return m_configCache.get();
}
ApolloConfig result = response.getBody();
logger.debug("Loaded config for {}: {}", m_namespace, result);
return result;
} catch (ApolloConfigStatusCodeException ex) {
ApolloConfigStatusCodeException statusCodeException = ex;
//config not found
if (ex.getStatusCode() == 404) {
String message = String.format(
"Could not find config for namespace - appId: %s, cluster: %s, namespace: %s, " +
"please check whether the configs are released in Apollo!",
appId, cluster, m_namespace);
statusCodeException = new ApolloConfigStatusCodeException(ex.getStatusCode(),
message);
}
Tracer.logEvent("ApolloConfigException", ExceptionUtil.getDetailMessage(statusCodeException));
transaction.setStatus(statusCodeException);
exception = statusCodeException;
} catch (Throwable ex) {
Tracer.logEvent("ApolloConfigException", ExceptionUtil.getDetailMessage(ex));
transaction.setStatus(ex);
exception = ex;
} finally {
transaction.complete();
}
// if force refresh, do normal sleep, if normal config load, do exponential sleep
onErrorSleepTime = m_configNeedForceRefresh.get() ? m_configUtil.getOnErrorRetryInterval() :
m_loadConfigFailSchedulePolicy.fail();
}
}方法三：
我们找到了RemoteConfigRepository类的scheduleLongPollingRefresh方法。
private void scheduleLongPollingRefresh() {
remoteConfigLongPollService.submit(m_namespace, this);
}点击submit方法，我们进入到了RemoteConfigLongPollService类里的该方法。
public boolean submit(String namespace, RemoteConfigRepository remoteConfigRepository) {
boolean added = m_longPollNamespaces.put(namespace, remoteConfigRepository);
m_notifications.putIfAbsent(namespace, INIT_NOTIFICATION_ID);
if (!m_longPollStarted.get()) {
// 长轮询获取配置
startLongPolling();
}
return added;
}private void startLongPolling() {
if (!m_longPollStarted.compareAndSet(false, true)) {
//already started
return;
}
try {
final String appId = m_configUtil.getAppId();
final String cluster = m_configUtil.getCluster();
final String dataCenter = m_configUtil.getDataCenter();
final long longPollingInitialDelayInMills = m_configUtil.getLongPollingInitialDelayInMills();
// 通过线程池获取配置
m_longPollingService.submit(new Runnable() {
@Override
public void run() {
if (longPollingInitialDelayInMills > 0) {
try {
logger.debug("Long polling will start in {} ms.", longPollingInitialDelayInMills);
TimeUnit.MILLISECONDS.sleep(longPollingInitialDelayInMills);
} catch (InterruptedException e) {
//ignore
}
}
// 获取apollo配置
doLongPollingRefresh(appId, cluster, dataCenter);
}
});
} catch (Throwable ex) {
m_longPollStarted.set(false);
ApolloConfigException exception =
new ApolloConfigException("Schedule long polling refresh failed", ex);
Tracer.logError(exception);
logger.warn(ExceptionUtil.getDetailMessage(exception));
}
}点击doLongPollingRefresh方法我们发现了HTTP长轮询获取配置的内容
private void doLongPollingRefresh(String appId, String cluster, String dataCenter) {
final Random random = new Random();
ServiceDTO lastServiceDto = null;
while (!m_longPollingStopped.get() && !Thread.currentThread().isInterrupted()) {
if (!m_longPollRateLimiter.tryAcquire(5, TimeUnit.SECONDS)) {
//wait at most 5 seconds
try {
TimeUnit.SECONDS.sleep(5);
} catch (InterruptedException e) {
}
}
Transaction transaction = Tracer.newTransaction("Apollo.ConfigService", "pollNotification");
String url = null;
try {
if (lastServiceDto == null) {
List<ServiceDTO> configServices = getConfigServices();
lastServiceDto = configServices.get(random.nextInt(configServices.size()));
}
url =
assembleLongPollRefreshUrl(lastServiceDto.getHomepageUrl(), appId, cluster, dataCenter,
m_notifications);
logger.debug("Long polling from {}", url);
HttpRequest request = new HttpRequest(url);
request.setReadTimeout(LONG_POLLING_READ_TIMEOUT);
transaction.addData("Url", url);
final HttpResponse<List<ApolloConfigNotification>> response =
m_httpUtil.doGet(request, m_responseType);
logger.debug("Long polling response: {}, url: {}", response.getStatusCode(), url);
if (response.getStatusCode() == 200 && response.getBody() != null) {
updateNotifications(response.getBody());
updateRemoteNotifications(response.getBody());
transaction.addData("Result", response.getBody().toString());
notify(lastServiceDto, response.getBody());
}
//try to load balance
if (response.getStatusCode() == 304 && random.nextBoolean()) {
lastServiceDto = null;
}
m_longPollFailSchedulePolicyInSecond.success();
transaction.addData("StatusCode", response.getStatusCode());
transaction.setStatus(Transaction.SUCCESS);
} catch (Throwable ex) {
lastServiceDto = null;
Tracer.logEvent("ApolloConfigException", ExceptionUtil.getDetailMessage(ex));
transaction.setStatus(ex);
long sleepTimeInSecond = m_longPollFailSchedulePolicyInSecond.fail();
logger.warn(
"Long polling failed, will retry in {} seconds. appId: {}, cluster: {}, namespaces: {}, long polling url: {}, reason: {}",
sleepTimeInSecond, appId, cluster, assembleNamespaces(), url, ExceptionUtil.getDetailMessage(ex));
try {
TimeUnit.SECONDS.sleep(sleepTimeInSecond);
} catch (InterruptedException ie) {
//ignore
}
} finally {
transaction.complete();
}
}
}对于长轮询获取配置的原因复制了另外一位老师的结论：
1.为什么不使用消息系统？太复杂，杀鸡用牛刀。
2.为什么不用 TCP 长连接？对网络环境要求高，容易推送失败。且有双写问题。
3.为什么使用 HTTP 长轮询？性能足够，结合 Servlet3 的异步特性，能够维持万级连接（一个客户端只有一个长连接）。直接使用 Servlet 的 HTTP 协议，比单独用 TCP 连接方便。HTTP 请求/响应模式，保证了不会出现双写的情况。最主要还是简单，性能暂时不是瓶颈。
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