failed to resolve 'api.sandbox.push.apple.com' after 3 queries？

[xuebin zhao]

Hello,everyone!

I have a problem about DNS when i send notifictions,this error alway comes up,but  not every time:

    java.net.UnknownHostException: failed to resolve 'api.sandbox.push.apple.com' after 3 queries？

This is my code:

    public void sendIOSListcast(List<String> deviceTokens, String text) throws NoSuchAlgorithmException, InvalidKeyException, IOException {

        if (apnsClient == null) {

            apnsClient = new ApnsClientBuilder().setApnsServer(ConstantImServerManage.APNS_HOST)

                    .setSigningKey(ApnsSigningKey.loadFromPkcs8File(new File(ConstantImServerManage.PATHNAME), ConstantImServerManage.TEAMID, ConstantImServerManage.KEYID)).build();

        }

        List<String> deviceTokensOfIOS =  deviceTokens.stream().filter(o -> !PushConfig.fun(o)).collect(Collectors.toList());

        for (int i = 0; i < deviceTokensOfIOS.size(); i++) {

            final SimpleApnsPushNotification pushNotification;

            final ApnsPayloadBuilder payloadBuilder = new SimpleApnsPayloadBuilder();

            payloadBuilder.addCustomProperty("message", text);

            payloadBuilder.setContentAvailable(true);

            final String payload = payloadBuilder.build();

            final String token = TokenUtil.sanitizeTokenString(deviceTokensOfIOS.get(i));

            pushNotification = new SimpleApnsPushNotification(token, ConstantImServerManage.TOPIC, payload);

            try {

            final PushNotificationFuture<SimpleApnsPushNotification, PushNotificationResponse<SimpleApnsPushNotification>>

                    sendNotificationFuture = apnsClient.sendNotification(pushNotification);

                final PushNotificationResponse<SimpleApnsPushNotification> pushNotificationResponse = sendNotificationFuture.get();

                if (pushNotificationResponse.isAccepted()) {

                    System.out.println("IOS Push notification accepted by APNs gateway. " + deviceTokensOfIOS.get(i));

                } else {

                    System.out.println("IOS Notification rejected by the APNs gateway: " + pushNotificationResponse.getRejectionReason() + " " + deviceTokensOfIOS.get(i));

                    pushNotificationResponse.getTokenInvalidationTimestamp().ifPresent(timestamp -> System.out.println("\t…and the token is invalid as of " + timestamp));

                }

            } catch (final ExecutionException | InterruptedException e) {

                System.out.println("IOS Failed to send push notification.");

            }

        }

    }

i use command "nslookup api.sandbox.push.apple.com" following result: