AWS SNS+Google FCM推送服務的使用

       近期在項目中需要用到AWS SNS服務，因爲面向安卓平臺，當然優先考慮谷歌的GCM（Google已更新爲FCM）搭配，在開發中遇到幾點問題，做一下記錄，順便給同行們參考。

       首先註冊/擁有Google賬號，在https://firebase.google.com/ 創建自己的項目，在Application欄添加自己的Android應用，根據提示一步步完成firebase的設置，生成對應的server_key即可，這裏基本不會有任何問題，谷歌的幫助文檔和截圖說明十分詳細。FCM設定完成後在Android App加入FirebaseMessagingService即可通過firebase的Cloud Messaging發送並測試FCM推送效果：

public class MyFirebaseMessagingService extends FirebaseMessagingService {

    @Override
    public void onMessageReceived(RemoteMessage remoteMessage) {
        Log.d("FCM", "onMessageReceived:" + remoteMessage.getFrom());
       
        // Check if message contains a data payload.
        if (remoteMessage.getData().size() > 0) {
            Log.d("FCM", "Message data payload: " + remoteMessage.getData());
        }

        // Check if message contains a notification payload.
        if (remoteMessage.getNotification() != null) {
            Log.d("FCM", "Message Notification Body: " + remoteMessage.getNotification().getBody());

            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O){
                createNotificationChannels(getApplicationContext());
            }else {
                sendNotification(remoteMessage.getNotification().getBody());
            }

        }
    }
}

       測試FCM可用後，開始創建自己的SNS服務，首先登陸AWS Console，在Services下拉菜單搜索SNS，就可以找到Simple Notification Service，然後按照SNS dashboard的Common Action完成create Topic 、Create platform application、Create Subscription、pulish Message 就可以發送Notification了，而爲了綁定先前創建的FCM應用，在Create platform application時需要選擇Push notification platform爲Google Cloud Messaging(GCM)，然後輸入在Firebase添加自己Android App時產生的api_key，而同時需要注意的是，若需要安卓設備能夠接收到Notification，需要在點擊application ARN，然後添加對應安卓設備的platform Endpoint，Create platform endpoint時需要輸入兩條數據，第二個user data爲用戶任意輸入內容，第一條的Device Token就是安卓設備從Google服務返回的token，取得Token需要在Android App加入FirebaseInstanceIdService，而爲了方便Endpoint的生成，我們可以將Token自動添加到Endpoint中，並創建與Topic對應的Subscription，使安卓用戶能夠自動實現接收Topic所發出的通知，代碼如下：

public class MyFirebaseInstanceIDService extends FirebaseInstanceIdService {
    public MyFirebaseInstanceIDService() {
    }

    @Override
    public void onTokenRefresh() {
        //For registration of token
        String refreshedToken = FirebaseInstanceId.getInstance().getToken();

        //To displaying token on logcat
        Log.d("TOKEN", refreshedToken);
        //upload token to SNS endpoint
        sendTokentoSNS(refreshedToken);
    }

    private void sendTokentoSNS(String refreshedToken){
        String access_id = "********"; 
        String secret_key ="********";
        String appArn = "arn:aws:sns:us-west-2:********:app/GCM/xxx_client"；
        String topicArn = "arn:aws:sns:us-west-2:********:ota-notify";
        AWSCredentials credentials = new BasicAWSCredentials(access_id,secret_key);
        AWSCredentialsProvider provider = new StaticCredentialsProvider(credentials);
        AmazonSNSClient snsClient = new AmazonSNSClient(provider);
                snsClient.setRegion(Region.getRegion(Regions.US_WEST_2));
        CreatePlatformEndpointRequest createPlatformEndpointRequest = new CreatePlatformEndpointRequest()
                .withPlatformApplicationArn()
                .withToken(refreshedToken)
                .withCustomUserData(Build.DEVICE);
        CreatePlatformEndpointResult result = snsClient.createPlatformEndpoint(createPlatformEndpointRequest);

        SubscribeRequest subscribeRequest = new SubscribeRequest().withTopicArn(topicArn)
                .withProtocol("application")
                .withEndpoint(result.getEndpointArn());
        snsClient.subscribe(subscribeRequest);
        Log.i("TOKEN","add token to SNS ");
    }

}

        以上基本實現了SNS通知接收和發送的框架，不過實際發送GCM通知時，還有一個問題需要解決，就是GCM在SNS裏Message的格式，怎樣發出對應的data和notification分類的消息，經過測試後，我使用了Gson來轉換SNS需要的格式，發送出一條包含data和notification的通知，代碼如下：

            String topicArn = "arn:aws:sns:us-west-2:********:ota-notify";
            //publish to an SNS topic
            String update = “a new update！”;
            
            Gson gson = new Gson();
            GCM gcm = new GCM();
            data data = new data();
            notification notification = new notification();
            SNSMessage snsMessage = new SNSMessage();
            
            notification.setTitle("AWS S3");
            notification.setSound("default");
            notification.setBody("you have "+update);
            data.setMessage("image update");
            gcm.setNotification(notification);
            gcm.setData(data);        
            snsMessage.setGcm(gson.toJson(gcm,GCM.class));
            snsMessage.setDefault("default message");                  
            
            String jsonstr = gson.toJson(snsMessage,SNSMessage.class);
            
            PublishRequest publishRequest = new PublishRequest()
                    .withTopicArn(topicArn)
                    .withSubject("update")
                    .withMessageStructure("json")                    
                    .withMessage(jsonstr);
    
            PublishResult publishResult = snsClient.publish(publishRequest);
            //print MessageId of message published to SNS topic
            System.out.println("MessageId - " + publishResult.getMessageId());