java connect to oss return UnknownHost

java code:    

private void ensureBucketExist(OSSClient client, String bucketName) {
        //就是这里报错，我在上传文件前先调用这个方法，确认bucket存在，但有些时候回出现unknownhost Exception（com.aliyun.oss.ClientException: UnknownHost）,
        //请教出现该问题该怎么解决
        boolean exists = client.doesBucketExist(bucketName);
        if (!exists) {
            client.createBucket(bucketName);
            client.setBucketAcl(bucketName, CannedAccessControlList.Private);
        }

    }