除去引入中间件的方式，Soul 网关还提供了 http 长轮询的方式进行数据的同步。
和其他方式一样，需要在 bootstrap 的 pom.xml 文件中引入如下依赖：
<!--soul data sync start use http--><dependency><groupId>org.dromara</groupId><artifactId>soul-spring-boot-starter-sync-data-http</artifactId><version>${last.version}</version></dependency>
在 yml 文件中进行如下配置：
soul :sync:http:url: http://localhost:9095
#url: 配置成你的 soul-admin的 ip与端口地址，多个admin集群环境请使用（,）分隔。
在 admin 模块的 yml 文件中进行下述配置：
soul:sync:http:enabled: true
HttpSyncDataService
由于长轮询的请求发起方是 bootstrap 模块，所以本篇文章从该模块开始进行 http 长轮询的源码阅读。
首先是 org.dromara.soul.sync.data.http.HttpSyncDataService 的构造方法：
public HttpSyncDataService(final HttpConfig httpConfig, final PluginDataSubscriber pluginDataSubscriber,final List<MetaDataSubscriber> metaDataSubscribers, final List<AuthDataSubscriber> authDataSubscribers) {
this.factory = new DataRefreshFactory(pluginDataSubscriber, metaDataSubscribers, authDataSubscribers);this.httpConfig = httpConfig;// 初始化服务端路由列表，以此支持多实例 adminthis.serverList = Lists.newArrayList(Splitter.on(",").split(httpConfig.getUrl()));// http 客户端初始化this.httpClient = createRestTemplate();this.start();}
Soul 使用了 OkHttp 进行 http 请求：
private RestTemplate createRestTemplate() {
OkHttp3ClientHttpRequestFactory factory = new OkHttp3ClientHttpRequestFactory();factory.setConnectTimeout((int) this.connectionTimeout.toMillis());factory.setReadTimeout((int) HttpConstants.CLIENT_POLLING_READ_TIMEOUT);return new RestTemplate(factory);}
构造方法最终执行了 start 方法，内容如下：
private void start() {
// It could be initialized multiple times, so you need to control that.// 防止多线程场景下多次调用的一致性问题if (RUNNING.compareAndSet(false, true)) {
// fetch all group configs.// 全量的拉取所有配置this.fetchGroupConfig(ConfigGroupEnum.values());int threadSize = serverList.size();// 初始化一个线程池，用于轮询线程的管理this.executor = new ThreadPoolExecutor(threadSize, threadSize, 60L, TimeUnit.SECONDS,new LinkedBlockingQueue<>(),SoulThreadFactory.create("http-long-polling", true));// start long polling, each server creates a thread to listen for changes.// 给每一个服务地址开启一个任务this.serverList.forEach(server -> this.executor.execute(new HttpLongPollingTask(server)));} else {
log.info("soul http long polling was started, executor=[{}]", executor);}}
进一步，我们查看拉取配置的方法
private void fetchGroupConfig(final ConfigGroupEnum... groups) throws SoulException {
for (int index = 0; index < this.serverList.size(); index++) {
String server = serverList.get(index);try {
this.doFetchGroupConfig(server, groups);break;} catch (SoulException e) {
// no available server, throw exception.if (index >= serverList.size() - 1) {
throw e;}log.warn("fetch config fail, try another one: {}", serverList.get(index + 1));}}}private void doFetchGroupConfig(final String server, final ConfigGroupEnum... groups) {
StringBuilder params = new StringBuilder();// 组装 URLfor (ConfigGroupEnum groupKey : groups) {
params.append("groupKeys").append("=").append(groupKey.name()).append("&");}String url = server + "/configs/fetch?" + StringUtils.removeEnd(params.toString(), "&");log.info("request configs: [{}]", url);String json = null;try {
// 使用上文中初始化的 HTTP 客户端进行请求json = this.httpClient.getForObject(url, String.class);} catch (RestClientException e) {
String message = String.format("fetch config fail from server[%s], %s", url, e.getMessage());log.warn(message);throw new SoulException(message, e);}// update local cache// 拿到结果后，更新本地缓存boolean updated = this.updateCacheWithJson(json);if (updated) {
log.info("get latest configs: [{}]", json);return;}// not updated. it is likely that the current config server has not been updated yet. wait a moment.log.info("The config of the server[{}] has not been updated or is out of date. Wait for 30s to listen for changes again.", server);ThreadUtils.sleep(TimeUnit.SECONDS, 30);}
接下来，我们回过头再阅读线程池中的长轮询任务：
public void run() {
while (RUNNING.get()) {
// 按照配置，进行重试for (int time = 1; time <= retryTimes; time++) {
try {
doLongPolling(server);} catch (Exception e) {
// print warnning log.if (time < retryTimes) {
log.warn("Long polling failed, tried {} times, {} times left, will be suspended for a while! {}",time, retryTimes - time, e.getMessage());ThreadUtils.sleep(TimeUnit.SECONDS, 5);continue;}// print error, then suspended for a while.log.error("Long polling failed, try again after 5 minutes!", e);ThreadUtils.sleep(TimeUnit.MINUTES, 5);}}}log.warn("Stop http long polling.");}private void doLongPolling(final String server) {
MultiValueMap<String, String> params = new LinkedMultiValueMap<>(8);// 组装 URLfor (ConfigGroupEnum group : ConfigGroupEnum.values()) {
ConfigData<?> cacheConfig = factory.cacheConfigData(group);String value = String.join(",", cacheConfig.getMd5(), String.valueOf(cacheConfig.getLastModifyTime()));params.put(group.name(), Lists.newArrayList(value));}HttpHeaders headers = new HttpHeaders();headers.setContentType(MediaType.APPLICATION_FORM_URLENCODED);HttpEntity httpEntity = new HttpEntity(params, headers);// 请求的路径为 /configs/listenerString listenerUrl = server + "/configs/listener";log.debug("request listener configs: [{}]", listenerUrl);JsonArray groupJson = null;try {
String json = this.httpClient.postForEntity(listenerUrl, httpEntity, String.class).getBody();log.debug("listener result: [{}]", json);groupJson = GSON.fromJson(json, JsonObject.class).getAsJsonArray("data");} catch (RestClientException e) {
String message = String.format("listener configs fail, server:[%s], %s", server, e.getMessage());throw new SoulException(message, e);}// 如果 listener 接口返回了数据，则重新获取相应组别的配置if (groupJson != null) {
// fetch group configuration async.ConfigGroupEnum[] changedGroups = GSON.fromJson(groupJson, ConfigGroupEnum[].class);if (ArrayUtils.isNotEmpty(changedGroups)) {
log.info("Group config changed: {}", Arrays.toString(changedGroups));this.doFetchGroupConfig(server, changedGroups);}}}
可以看到，轮询的任务会先调用 /configs/listener 接口获取哪些组别（比如 RULE）的配置发生了变化，当获取到变化时，再调用 /configs/fetch 拉取相应组别的配置，注意，此时是全量拉取。
ConfigController
在前文的探索中，可以发现 http 长轮询只涉及到两个接口，它们都在 org.dromara.soul.admin.controller.ConfigController 中被定义。而每个接口都依赖 org.dromara.soul.admin.listener.http.HttpLongPollingDataChangedListener
先从 /listener 接口开始看：
@PostMapping(value = "/listener")public void listener(final HttpServletRequest request, final HttpServletResponse response) {
longPollingListener.doLongPolling(request, response);}public void doLongPolling(final HttpServletRequest request, final HttpServletResponse response) {
// compare group md5// 获取有变化的组List<ConfigGroupEnum> changedGroup = compareChangedGroup(request);String clientIp = getRemoteIp(request);// response immediately.if (CollectionUtils.isNotEmpty(changedGroup)) {
this.generateResponse(response, changedGroup);log.info("send response with the changed group, ip={}, group={}", clientIp, changedGroup);return;}// listen for configuration changed.// 使用异步的方式进行请求处理final AsyncContext asyncContext = request.startAsync();// AsyncContext.settimeout() does not timeout properly, so you have to control it yourselfasyncContext.setTimeout(0L);// block client's thread.// 将异步的上下文放入线程池，将在最多 60 秒的等待被执行scheduler.execute(new LongPollingClient(asyncContext, clientIp, HttpConstants.SERVER_MAX_HOLD_TIMEOUT));}
接下来需要注意的是，上述代码块中最后放入线程池的任务，会最终进入 HttpLongPollingDataChangedListener 维护的一个 BlockingQueue 中，以下是 LongPollingClient 的 run() 方法：
@Overridepublic void run() {
// 生成一个定时执行的任务this.asyncTimeoutFuture = scheduler.schedule(() -> {
clients.remove(LongPollingClient.this);List<ConfigGroupEnum> changedGroups = compareChangedGroup((HttpServletRequest) asyncContext.getRequest());sendResponse(changedGroups);}, timeoutTime, TimeUnit.MILLISECONDS);// 最终放入任务队列中clients.add(this);}
除去上述的执行方式，也有在配置修改时返回 response 的逻辑：
HttpLongPollingDataChangedListener 中也实现了 afterRuleChanged 方法，这个方法向线程池中放入了 DataChangeTask 任务：
@Overridepublic void run() {
for (Iterator<LongPollingClient> iter = clients.iterator(); iter.hasNext();) {
// 获取到一个正在等待响应的客户端线程LongPollingClient client = iter.next();iter.remove();// 发出响应client.sendResponse(Collections.singletonList(groupKey));log.info("send response with the changed group,ip={}, group={}, changeTime={}", client.ip, groupKey, changeTime);}}