Запускаем Telegram-бота на Android устройстве

private void getUpdates(final TelegramBot bot) {
        try {
            GetUpdatesResponse response = bot.execute(
                    new GetUpdates()
                            .limit(LIMIT)
                            .offset(updateId.get())
                            .timeout(LONG_POLLING_TIMEOUT));

            if (response != null && response.updates() != null && response.updates().size() > 0) {
                for (Update update : response.updates()) {
                    obtainUpdate(bot, update);
                    updateId.set(update.updateId() + 1);
                }
            }
        } catch (Exception e) {
            ErrorUtils.log(TAG, e);
        }
    }

public class PushHelper {
    private static final String URL = "https://fcm.googleapis.com/fcm/send";
    private static java.util.logging.Logger log = java.util.logging.Logger.getLogger(PushHelper.class.getName());
    private static final MediaType JSON = MediaType.parse("application/json; charset=utf-8");
    private static final String AUTHORIZATION = "...";

    public static String push(PushRequest pushRequest) throws IOException {
        ObjectMapper objectMapper = new ObjectMapper();
        return post(URL, objectMapper.writeValueAsString(pushRequest));
    }

    private static String post(String url, String json) throws IOException {
        RequestBody body = RequestBody.create(JSON, json);
        Request request = new Request.Builder()
                .url(url)
                .header("Authorization", AUTHORIZATION)
                .post(body)
                .build();
        OkHttpClient client = getSslClient();
        if (client != null) {
            Response response = client.newCall(request).execute();
            return response.body().string();
        } else {
            throw new IOException("Unable to init okhttp client");
        }
    }
...
}

public class PushRequest {
    private PushData data; //Данные, отправляемые на устройство
    private String to;  //Пуш-токен устройства
    private String priority = "high"; //Приоритет сообщения
    ...
}

Для того, чтобы сообщение приходило даже когда устройство находится в состоянии сна, нужно указать priority = «high»

openssl req -newkey rsa:2048 -sha256 -nodes -keyout private.key -x509 -days 365 -out public_cert.pem -subj "/C=RU/ST=State/L=Location/O=Organization/CN=ServerHost"

openssl pkcs12 -export -in public_cert.pem -inkey private.key -certfile public_cert.pem -out keystore.p12
keytool -importkeystore -srckeystore keystore.p12 -srcstoretype pkcs12 -sigalg SHA1withRSA -destkeystore keystore.jks -deststoretype JKS
rm keystore.p12
rm private.key

private Observable<TdApi.Message> sendMessage(long chatId, String text) {
        return Observable.create(subscriber -> {
            telegramClient.sendMessage(chatId, text, object -> {
                if (object instanceof TdApi.Error) {
                    subscriber.onError(new Throwable(((TdApi.Error) object).message));
                } else {
                    TdApi.Message message = (TdApi.Message) object;
                    subscriber.onNext(message);
                }
            });
        }).delay(5, TimeUnit.SECONDS).flatMap(msg -> getLastIncomingMessage(((TdApi.Message) msg).chatId, ((TdApi.Message) msg).senderUserId, ((TdApi.Message) msg).id));
    }

    private Observable<TdApi.Message> getLastIncomingMessage(long chatId, int userId, int outgoingMessageId) {
        return Observable.create(subscriber -> {
            telegramClient.getLastIncomingMessage(chatId, outgoingMessageId, userId, object -> {
                if (object instanceof TdApi.Error) {
                    subscriber.onError(new Throwable(((TdApi.Error) object).message));
                } else {
                    TdApi.Message message = (TdApi.Message) object;
                    subscriber.onNext(message);
                }
            });
        });
    }

public class TelegramClient {
    private final Client client;

    public TelegramClient(Context context, Client.ResultHandler updatesHandler) {
        TG.setDir(context.getCacheDir().getAbsolutePath());
        TG.setFilesDir(context.getFilesDir().getAbsolutePath());
        client = TG.getClientInstance();
        TG.setUpdatesHandler(updatesHandler);
    }

    public void clearAuth(Client.ResultHandler resultHandler) {
        TdApi.ResetAuth request = new TdApi.ResetAuth(true);
        client.send(request, resultHandler);
    }

    public void getAuthState(Client.ResultHandler resultHandler) {
        TdApi.GetAuthState req = new TdApi.GetAuthState();
        client.send(req, resultHandler);
    }

    public void sendPhone(String phone, Client.ResultHandler resultHandler) {
        TdApi.SetAuthPhoneNumber smsSender = new TdApi.SetAuthPhoneNumber(phone, false, true);
        client.send(smsSender, resultHandler);

    }

    public void checkCode(String code, String firstName, String lastName, Client.ResultHandler resultHandler) {
        TdApi.CheckAuthCode request = new TdApi.CheckAuthCode(code, firstName, lastName);
        client.send(request, resultHandler);
    }


    public void sendMessage(long chatId, String text, Client.ResultHandler resultHandler) {
        TdApi.InputMessageContent msg = new TdApi.InputMessageText(text, false, false, null, null);
        TdApi.SendMessage request = new TdApi.SendMessage(chatId, 0, false, false, null, msg);
        client.send(request, resultHandler);
    }

    public void getLastIncomingMessage(long chatId, int fromMessageId, int userId, Client.ResultHandler resultHandler) {
        getChat(chatId, chatObj -> {
            if (chatObj instanceof TdApi.Chat) {
                TdApi.GetChatHistory getChatHistory = new TdApi.GetChatHistory(chatId, fromMessageId, -1, 2);
                client.send(getChatHistory, messagesObj -> {
                    if (messagesObj instanceof TdApi.Messages) {
                        TdApi.Messages messages = (TdApi.Messages) messagesObj;
                        if (messages.totalCount > 0) {
                            for (TdApi.Message message : messages.messages) {

                                if (message.id != fromMessageId && message.senderUserId != userId) {
                                    resultHandler.onResult(message);
                                    return;
                                }
                            }
                        }
                        resultHandler.onResult(new TdApi.Error(0, "Unable to get incoming message"));
                    } else resultHandler.onResult(messagesObj);
                });
            } else resultHandler.onResult(chatObj);
        });


    }

    public void getChat(long chatId, Client.ResultHandler resultHandler) {
        TdApi.GetChat getChat = new TdApi.GetChat(chatId);
        client.send(getChat, resultHandler);
    }


    public void searchContact(String username, Client.ResultHandler resultHandler) {
        TdApi.SearchPublicChat searchContacts = new TdApi.SearchPublicChat(username);
        client.send(searchContacts, resultHandler);
    }

    public void getMe(Client.ResultHandler resultHandler) {
        client.send(new TdApi.GetMe(), resultHandler);
    }

    public void changeUsername(String username, Client.ResultHandler resultHandler) {
        client.send(new TdApi.ChangeUsername(username), resultHandler);
    }

    public void startChatWithBot(int botUserId, long chatId, Client.ResultHandler resultHandler) {

        TdApi.CloseChat closeChat = new TdApi.CloseChat(chatId);
        client.send(closeChat, resClose -> {
            TdApi.OpenChat openChat = new TdApi.OpenChat(chatId);
            client.send(openChat, resOpen -> {
                if (resOpen instanceof TdApi.Error) {
                    resultHandler.onResult(resOpen);
                    return;
                }

                TdApi.SendBotStartMessage request = new TdApi.SendBotStartMessage(botUserId, chatId, "/start");
                client.send(request, resultHandler);
            });
        });
    }

    public void logout(Client.ResultHandler resultHandler) {
        client.send(new TdApi.ResetAuth(false), resultHandler);
    }
}