使用JMessage会偶尔打出如下日志，请问是什么原因
```
cn.jiguang.common.resp.APIConnectionException: Connection IO error.
Can not connect to JPush Server. Please ensure your internet connection is ok.
If the problem persists, please let us know at support@jpush.cn.
at cn.jiguang.common.connection.NativeHttpClient._doRequest(NativeHttpClient.java:249)
at cn.jiguang.common.connection.NativeHttpClient.doRequest(NativeHttpClient.java:99)
at cn.jiguang.common.connection.NativeHttpClient.sendGet(NativeHttpClient.java:71)
at cn.jiguang.common.connection.NativeHttpClient.sendGet(NativeHttpClient.java:66)
at cn.jmessage.api.user.UserClient.getUserState(UserClient.java:110)
at cn.jmessage.api.JMessageClient.getUserState(JMessageClient.java:140)
at com.codyy.cloudschool.mms.service.impl.JiguangServiceImpl.sendMessageToPc(JiguangServiceImpl.java:124)
at sun.reflect.GeneratedMethodAccessor203.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:333)
at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:190)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:157)
at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:92)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:213)
at com.sun.proxy.$Proxy96.sendMessageToPc(Unknown Source)
at com.codyy.cloudschool.mms.rpc.impl.MmsServiceCallImpl$MsgSendThread.run(MmsServiceCallImpl.java:513)
at java.lang.Thread.run(Thread.java:748)
Caused by: java.net.UnknownHostException: api.im.jpush.cn
at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:184)
at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
at java.net.Socket.connect(Socket.java:589)
at sun.security.ssl.SSLSocketImpl.connect(SSLSocketImpl.java:673)
at sun.net.NetworkClient.doConnect(NetworkClient.java:175)
at sun.net.www.http.HttpClient.openServer(HttpClient.java:463)
at sun.net.www.http.HttpClient.openServer(HttpClient.java:558)
at sun.net.www.protocol.https.HttpsClient.<init>(HttpsClient.java:264)
at sun.net.www.protocol.https.HttpsClient.New(HttpsClient.java:367)
at sun.net.www.protocol.http.HttpURLConnection.plainConnect0(HttpURLConnection.java:1138)
at sun.net.www.protocol.http.HttpURLConnection.plainConnect(HttpURLConnection.java:1032)
at sun.net.www.protocol.http.HttpURLConnection.getInputStream0(HttpURLConnection.java:1546)
at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1474)
at java.net.HttpURLConnection.getResponseCode(HttpURLConnection.java:480)
at sun.net.www.protocol.https.HttpsURLConnectionImpl.getResponseCode(HttpsURLConnectionImpl.java:338)
at cn.jiguang.common.connection.NativeHttpClient._doRequest(NativeHttpClient.java:166)