I want to have a Java-Application that is behind a firewall (maybe even connected over a 3G modem) and I have a google app-engine application.
How can the gae app push data to the clients?
I found some ways that look promising, but I'm not sure what will really work.
Sockets will not work, because I cannot connect through the firewall/3G barrier
the channel API only works with JS clients
XMPP looks very promising - the client would report it's presence and the server could push chat-messages to the client and also the client could reply that way.
But what about user-accounts? i.e. could I use a single XMPP-account for all users (and let the client send a unique ID to identify the user) - or is a unique XMPP account for every device (which runs the java-aplication behind the firewall) required?
are there any other options or are there some XMPP gotcha's you know about?
Related
I have a very basic design of my entire application, where several users with my app on there android devices commits data to the server (I have used REST web services(java) + postgresql as my server) through HTTP post request from the android application. I am successful in achieving this and app runs absolutely fine. Now i want to implement a scenario where any change(CRUD operations) on my db on server should create a notification on my users android device. How should i achieve this with my server design unchanged? I have looked into Google Cloud Messaging, but could figure out the server implementation.
For now i have implemented db triggers on postgresql and able to get control back into java code using Notify/Listen feature of postgresql. From here i need to connect to android device. How can this be achieved. Is Google Cloud Messaging the only way? I have not seen any insert/update statements in there server implementation. Could anyone please guide me on this?
either you can use GCM or implement a Socket at server end and open a socket connection from mobile but this approach may add some additional processing overhead because it will create a daemon thread to listen socket port from mobile device.
You should use native library (NotificationManager etc.), here you can find a great tutorial.
My Advice is for you to use GCM. GCM normally takes a maximum of 4kb, so you could have your own defined "commands". You could use them to determine the requests on both ends, ie on android app and the server end. A php script on the server would help you in this.
I am working on an app where by the android app sends messages to the server via POST and the server forwards the message to the appropriate user via GCM. In my case I have very many things to share so in that case I am using commands, for example if it is a new incoming message I send a GCM to the app with one variable as the command and the rest as the data. On the android app I use the command variable to determine what to do with the data.
Kindly avoid that socket advice, it will have your app drain the battery to sustain the open socket , besides you don't have to re-invent the wheel while Google servers already has it
when building a server, one sometimes performs asynchronous tasks from client to server (which responds to client in asynchronous time),
or the server needs to send the client a message
now if the client is listening at all times (meaning polling) it takes a lot of resources which is problematic
here is where I assume the operating system steps in and assumes the role of polling for the appropriate port, and letting the application know using the appropriate event (the application subscribes using the OS API)
am I right in my assumptions?
how do I subscribe to a port using the OS's API? (lets say android for the sake of argument)
how is a message from server to client work exactly?
and how does the server know the client's IP at all times?
I have seen many questions in the subject, but wasn't able to figure out the big picture
Edit:
I am using GCM in android, but have seen other apps that does not use it and still manage to do it right, also it's a more general question as to what is the right approach in java VS. any operating system it uses (ubnutu, windows, android, etc.)
Totally right - polling is typically a waste of resources. Until recently, many apps would either keep a socket open and poll every few minutes to keep it alive, or make periodic HTTP calls to a server.
Nowadays, Google Cloud Messaging is used by most apps to push data instead of constantly polling. As you correctly guessed, this is implemented by maintaining a persistent connection with Google's servers. The advantage of this is that it's very efficient for battery life, and that all apps can use this one resource to send push notifications, instead of each app having to poll a different server or create its own persistent connection.
The idea is that you send requests to GCM from your server (this can be in response to user activity, etc), which sends it to all of the client's devices. You can either send a message with a small payload (up to 4kb) or a "send-to-sync" message, which tells an app to contact the server (e.g. to sync new data from the server after user changes).
here is where I assume the operating system steps in and assumes the role of polling for the appropriate port, and letting the application know using the appropriate event (the application subscribes using the OS API)
GCM pushes messages to clients, so there isn't active waiting like you'd see in a simple polling system.
how is a message from server to client work exactly? and how does the server know the client's IP at all times?
There's no need for servers to know the client IP, as any online android device will typically maintain a connection with GCM. Targeting specific users is done via User Notifications.
(Oh, and I realize that your question is more general than just Android, which I have more experience in, but iOS has a similar system in place. Some developers I've met like to use Parse for managing push notifications).
I built an Android application with Google App Engine Server. Now I want to add simple chat to my app. And I have some questions.
My users registered with theirs desired email domains like hotmail.com, yahoo.com and even more esoteric domains, thats mean that I need to create JID for them? if so is Google App engine provide JID creations with my app domain that i can manipulate?
I read that Google App Engine act as XMPP client so I need Xmpp Server that can receive and send XMPP messages. So why do I GAE for? is Openfire is my answer? can I integrate Openfire with GAE?
I Also read that if I want to use XMPP in GAE and Android in need aSmack Api for my client and that it is working on HTTP. So I guess that I'll need to poll the server for messages every couple seconds. Is there a better pattern?
can I integrate Openfire with GAE?
You cannot run Openfire on GAE because GAE works only on HTTP so you won't be able to connect over sockets as Openfire does.
My users registered with theirs desired email domains like hotmail.com, yahoo.com and even more esoteric domains, thats mean that I need to create JID for them? if so is Google App engine provide JID creations with my app domain that i can manipulate?
If I understand your question correctly, you shouldn't have any problems here. As long as you're not a spammer, we don't place any restrictions on what domains you can send to.
I read that Google App Engine act as XMPP client so I need Xmpp Server that can receive and send XMPP messages. So why do I GAE for? is Openfire is my answer? can I integrate Openfire with GAE?
You can send and receive XMPP messages via the xmpp API (this is the python version). This calls into the Google Talk infrastructure. You don't have access to what you'd traditionally call an "XMPP server", but you do have access to basic XMPP functionality.
I don't know a lot about OpenFire, but there is a Trusted Tester program for outbound sockets that you can sign up for. This is what you would need if you desire an external XMPP server.
I Also read that if I want to use XMPP in GAE and Android in need aSmack Api for my client and that it is working on HTTP. So I guess that I'll need to poll the server for messages every couple seconds. Is there a better pattern?
I should prefix this by saying I don't know a whole lot about Android or aSmack, but that won't stop me from taking a stab at answering your question. :-)
I think this depends on your usecase, but I can't think of any situation you'd need to do this off the top of my head. Will the user of your application have their own JID on a server they registered for? If so, I don't see any reason you'd have to connect via HTTP, unless that's all aSmack supports. The main use-case for BOSH/XMPP-over-HTTP is in the browser where you don't really have access to open raw sockets.
If you want to use XMPP as a messaging/notification service the user won't know about, it may be more complex. I should note that you can always set up an XMPP server on Google Compute Engine.
I have an IRC bot written entirely in Java that I've been hosting on my home computer, but my iffy internet connection has been disconnecting it a lot. I've been wondering if I could use the Google Apps Engine to host the bot with a constant connection? If so, what kind of changes am I going to have to make?
Thanks for the help
No, you cannot do that. Google App Engine does not allow arbitrary outgoing Socket connections (probably because they do not want people using their platform as a proxy server). The closest thing they offer is the URL Fetch API for accessing external content over the network/Internet.
Using that, you might be able to come up with something that drives an existing web-based IRC client using an App Engine app. Though I'm not sure what benefit that would have over just using a web-based IRC client directly.
Also you cannot have a "constant connection" to (or from) an App Engine app. The platform will automatically time-out/close any request that has not completed processing within about 30 seconds or so.
I would like to use XMPP so that my application will send out updates to an android phone (1.5 and higher). I pretty much want to use XMPP to send push notifications to the phone.
How would i go about achieving this. At the moment my web application is running on apache tomact with a number of servlets so the android phone can access information, but I'm finding it difficult understanding how I could implement XMPP so that I can push information from the server to the client (android phone).
I have tested the below tutorial
Example of XMPP with Google ID login
It uses Google ID logins. But i need to use my webapplication to do what google implements.
Any ideas?
That would depend on the nature of your push (is it a point to point or pub sub). In either case, you will need an XMPP server that your clients and application are connected to. This will be the means for your application to send notifications to the clients.
Not sure what you mean by "I need to use my webapplication to what google implements". Your webapplication would be a client to the xmpp server, just like your phones. You cannot use xmpp to simply talk to your webapplication, unless it happens to be a bosh enabled xmpp server itself, which I would guess is not likely.
You can use Smack for your client communications, and any one of the many available servers.
If the communication is directed at specific clients, then creating a chat between the application and client is probably the simplest means. If it is more of a broadcast, then you could use either MUC (multi user chat) or pubsub.
Generally, you would implement this as a pub-sub feature. Pub-sub is basically the publish/ subscribe paradigm: you publish something and they receive it.
Assuming you have an XMPP server setup that supports the pub-sub protocol extension (like eJabber), in your app, you would login to that server and subscribe to a node (where your update notifications would be sent), and with your subscription you would have to add a handler to handle any notification on that node.
On the server side, when you have something that all of your clients need to know about, you would publish the update to the same node that the clients subscribe to.
For more info, see http://xmpp.org/extensions/xep-0060.html