我已经实现了订阅特定主题的 pubsub poller，然后安排在指定间隔轮询新消息的任务。
我看到它偶尔会收到 UnknownHostException 导致没有收到任何消息 -
java.net.UnknownHostException: accounts.google.com
at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:184) ~[na:1.8.0_25]
at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392) ~[na:1.8.0_25]
at java.net.Socket.connect(Socket.java:589) ~[na:1.8.0_25]
at sun.security.ssl.SSLSocketImpl.connect(SSLSocketImpl.java:649) ~[na:1.8.0_25]
at sun.net.NetworkClient.doConnect(NetworkClient.java:175) ~[na:1.8.0_25]
at sun.net.www.http.HttpClient.openServer(HttpClient.java:432) ~[na:1.8.0_25]
at sun.net.www.http.HttpClient.openServer(HttpClient.java:527) ~[na:1.8.0_25]
at sun.net.www.protocol.https.HttpsClient.<init>(HttpsClient.java:275) ~[na:1.8.0_25]
at sun.net.www.protocol.https.HttpsClient.New(HttpsClient.java:371) ~[na:1.8.0_25]
at sun.net.www.protocol.https.AbstractDelegateHttpsURLConnection.getNewHttpClient(AbstractDelegateHttpsURLConnection.java:191) ~[na:1.8.0_25]
at sun.net.www.protocol.http.HttpURLConnection.plainConnect0(HttpURLConnection.java:1103) ~[na:1.8.0_25]
at sun.net.www.protocol.http.HttpURLConnection.plainConnect(HttpURLConnection.java:997) ~[na:1.8.0_25]
at sun.net.www.protocol.https.AbstractDelegateHttpsURLConnection.connect(AbstractDelegateHttpsURLConnection.java:177) ~[na:1.8.0_25]
at sun.net.www.protocol.http.HttpURLConnection.getOutputStream0(HttpURLConnection.java:1281) ~[na:1.8.0_25]
at sun.net.www.protocol.http.HttpURLConnection.getOutputStream(HttpURLConnection.java:1256) ~[na:1.8.0_25]
at sun.net.www.protocol.https.HttpsURLConnectionImpl.getOutputStream(HttpsURLConnectionImpl.java:250) ~[na:1.8.0_25]
at com.google.api.client.http.javanet.NetHttpRequest.execute(NetHttpRequest.java:77) ~[google-http-client-1.22.0.jar:1.22.0]
at com.google.api.client.http.HttpRequest.execute(HttpRequest.java:981) ~[google-http-client-1.22.0.jar:1.22.0]
at com.google.api.client.auth.oauth2.TokenRequest.executeUnparsed(TokenRequest.java:283) ~[google-oauth-client-1.22.0.jar:1.22.0]
at com.google.api.client.auth.oauth2.TokenRequest.execute(TokenRequest.java:307) ~[google-oauth-client-1.22.0.jar:1.22.0]
at com.google.api.client.googleapis.auth.oauth2.GoogleCredential.executeRefreshToken(GoogleCredential.java:384) ~[google-api-client-1.22.0.jar:1.22.0]
at com.google.api.client.auth.oauth2.Credential.refreshToken(Credential.java:489) ~[google-oauth-client-1.22.0.jar:1.22.0]
at com.google.api.client.auth.oauth2.Credential.intercept(Credential.java:217) ~[google-oauth-client-1.22.0.jar:1.22.0]
at com.google.api.client.http.HttpRequest.execute(HttpRequest.java:868) ~[google-http-client-1.22.0.jar:1.22.0]
at com.google.api.client.googleapis.services.AbstractGoogleClientRequest.executeUnparsed(AbstractGoogleClientRequest.java:419) ~[google-api-client-1.22.0.jar:1.22.0]
at com.google.api.client.googleapis.services.AbstractGoogleClientRequest.executeUnparsed(AbstractGoogleClientRequest.java:352) ~[google-api-client-1.22.0.jar:1.22.0]
at com.google.api.client.googleapis.services.AbstractGoogleClientRequest.execute(AbstractGoogleClientRequest.java:469) ~[google-api-client-1.22.0.jar:1.22.0]
at com.company.events.subscriber.PubsubPollerImpl.doPoll(PubsubPollerImpl.java:86) [classes/:na]
at com.company.events.subscriber.PubsubPollerImpl.poll(PubsubPollerImpl.java:58) [classes/:na]
at com.company.events.subscriber.PollingEventListenerContainer.pull(PollingEventListenerContainer.java:132) [classes/:na]
at com.company.events.subscriber.PollingEventListenerContainer.lambda$scheduleRecurring$0(PollingEventListenerContainer.java:120) [classes/:na]
at com.company.events.subscriber.PollingEventListenerContainer$$Lambda$1/777341499.run(Unknown Source) [classes/:na]
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [na:1.8.0_25]
at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:308) [na:1.8.0_25]
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:180) [na:1.8.0_25]
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:294) [na:1.8.0_25]
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) [na:1.8.0_25]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) [na:1.8.0_25]
at java.lang.Thread.run(Thread.java:745) [na:1.8.0_25]