短信上行SDK服务器无法连接怎么解决

20:30:49,972 ERROR DefaultAlicomMessagePuller:150 - PullMessageTask_execute_error,messageType:SmsUp,queueName:Alicom-Queue-1931739184491719-SmsUp
com.aliyuncs.exceptions.ClientException: SDK.ServerUnreachable : Server unreachable: javax.net.ssl.SSLHandshakeException: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
    at com.aliyuncs.DefaultAcsClient.doAction(DefaultAcsClient.java:207)
    at com.aliyuncs.DefaultAcsClient.doAction(DefaultAcsClient.java:152)
    at com.aliyuncs.DefaultAcsClient.doAction(DefaultAcsClient.java:60)
    at com.aliyuncs.DefaultAcsClient.getAcsResponse(DefaultAcsClient.java:104)
    at com.alicom.mns.tools.TokenGetterForAlicom.getTokenFromRemote(TokenGetterForAlicom.java:70)
    at com.alicom.mns.tools.TokenGetterForAlicom.getTokenByMessageType(TokenGetterForAlicom.java:99)
    at com.alicom.mns.tools.DefaultAlicomMessagePuller$PullMessageTask.run(DefaultAlicomMessagePuller.java:106)
    at java.lang.Thread.run(Thread.java:619)