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Restful Server Response triggered Via Client

This question might sound a bit abstract,answered (but did my search didn't stumble on a convenient answer) or not specific at all ,but I will try to provide as much information as I can.
I am building a mobile application which will gather and send sensory data to a remote server. The remote server will collect all these data in a mySQL database and make computations (not the mysql database ,another process/program) . What I wanna know is :
After some updates in the database , is it doable to send a response from a RESTful Server to a certain client (the one who like did the last update probably) ,using something like "a background thread"? Or this should be done via socket connection through server-client response?
Some remarks:
I am using javaEE, Spring MVC with hibernate and tomcat (cause I am familiar with the environment though in a more asynchronous manner).
I thought this would be a convenient way because the SQL schema is not much complicated and security and authentication issues are not needed (it's a prototype).
Also there is a front-end webpage that will have to visualize these data, so such a back-end system would look like a good option for getting the job done fast.
Lastly I saw this solution :
Is there a way to 'listen' for a database event and update a page in real time?
My issue is that besides the page I wanna update the client's side with messages from the RESTful server.
If all these above are unecessary and a more simple client-server application will prove better and less complex please be welcome to inform me.
Thank you in advance.

Generally you should upload your data to a resource on the server (e.g. POST /widgets and the server should immediately return with a 201 Created or (if creation is too slow and needs to happen later) 202 Accepted status. There are several approaches after that happens, each has their merits:
Polling - The server's response includes a location field which the client can then proceed to poll until a change happens (e.g. check for an update every second). This is the easiest approach and quite efficient if you use HTTP caching effectively and the average number of checks is relatively low.
Push notification - Server sends a push notification when the change happens, report's generated, etc. Obviously this requires you to store the client's details and their notification requirements. This is probably the cleanest approach and also easy to scale. In the case of Android (also iOS) you have free push notifications available via Google Cloud Messaging.
Set up a persistent connection between client and server, e.g. using a Websocket or low-level TCP connection. This should yield the fastest response times, but will probably be a drain on phone battery, harder to scale on the server, and more complex to code.

Systemdesign: Webserver, API and Database

Currently i have a website offering some product. The webserver sits on the same system as the database and directly accesses it to retrieve the required information for the HTML frontend. Now i think it is good to separate the database from the webserver via an API server. The reason why i want to use an API server is that it might be possible that future applications, other than the website, will need access to the information on the system.
The system which i want should consist of the following components:
A database which will store all the required information.
An API server which will be implemented in Java and should use oauth2 for authorizing user requests. The API server will have the only direct connection to the database.
A webserver.
So basically what i have in mind is that i want to build my website on top of that API server. The user will register/login/... over the website and the website implementation will internally query the API server as a webservice on behalf of the user. The API server would then return the data from the database. That way the HTML frontend is just an application using the API server and will never itself be in direct contact with the database.
I think that this is an often encountered problem for which a good solution exists. I am unsure if this solution is the way to go though. Could you help me out and/or point me in the right direction from here?
Thank you.

As far as I know, it is not advisable to have a separate API server for a couple of reasons: decreasing performance and increasing compexity of a system. So basically you should avoid this type of solution for as long as possible.
You should definitely read M. Fowler: "Enterprise Architecture Patterns" for inspiration.
Returning to your question: have you considered making this API layer as a module (library)?
If I haven't convinced you, try reading Java RMI documentation (http://www.oracle.com/technetwork/java/javase/tech/index-jsp-136424.html)

How can I get a server to notify the client about changes using the spring Framework?

I'm starting to develop what should become a client-server Application using Hibernate, Spring and Eclipse RCP (for the client). This is the first time I'm designing an application from the beginning so I'm just making my first steps.
I have set up Spring on both client and server using RMI for remoting (but I wouldn't mind using something else if there was a clear advantage). So right now I'm able to call exposed services of the server from different clients to get information from the database. What I haven't done is get any kind of authentication in place, so basically the server just answers to the different clients without knowing anything about them, there is not concept of a session yet. Of course this has to change since I need different user to have different roll and so on, but right now the problem I'm facing is getting the server to notify the client when certain thing happen.
My idea to solve this problem was to have a queue of events at the Server and have the clients get them every 3 second or so. The server would then identify the client by it's session token and send the appropriate events. Yet my partner in this project is concerned that this technique (polling) might waste too much bandwidth unnecessarily.
So to bring it to the point. What are the standard techniques for a server to notify a client about changes using Spring? Please notice that I'm not developing a web application and that this is only intended to be used withing a private network. That is one of the difficulties I've been facing: every single tutorial about Spring security or remoting assumes you are making a web application, but I really don't want to get lost into the details of Spring MVC and web applications in general.
Any resources would be appreciated. A good and long tutorial on the matter would be great.
EDIT: Hmm, it looks like JMS might be what I'm looking for.

As I understand, the issues you are facing is identifying a client in request and correlate different client request i.e. have something like a session.
Spring also support RMI over HTTP protocol (Using Hessian and its own HTTP Invokers). Check out this link (Section 17.3). Now once you have transport as HTTP, it has inherent Basic Authentication and session which can be leveraged to get around the issues you are facing.
This is just a pointer. I would be curious to know how eventually you resolved your problem.

how MVC Pattern can be realized in RMI multiuser application?

i am trying to create framework/library /API for creating small multiuser games, in which the goal is to achieve 'decoupling' between the server, client and business logic.
The server in my case is kind of registering the clients and sent that
list to business logic, clients are registering with the server,
and the business logic do the game logic stuff and updates the client by getting the list of client from server.
But currently,
i have only one class, so its trivial but this could consist of several game objects
(and what would be the role of classes serialized/remote
like the game engine, player, score, move, board).
i decided to use the RMI for this and this will definitely use callback
mechanism can somebody told me.
How could i achieve this encorporating all the requirement of server updating clients (callbacks).
PS:i m currently working on the design, which has one remote/serialized object for handling gamelogic but i wanted to
use other classes as i mentioned for sake of making multiuser game library and to show the use of important classes in it as an example.
thanks a lot
jibby

If you are intending this framework to work for real time games then I would advise against using RMI - it isn't really designed for that sort of thing. Also be aware that two-way RMI between machines on different subnets is very hard to get working.
It seems as if you need the clients to be informed by the server when events occur. When your client connects it can lookup a Remote object from the server's RMI registry and call a method on that to pass a Remote object it has created (hosted on the client) to the server. The server will have to maintain a collection of these client objects and iterate through them to send events. This is a tricky architecture to get right as if the network goes down or a client goes offline you will have to deal with all sorts of nasty error handling and freeze ups. I would recommend you keep the majority of communication in one direction - from client to server. Also keep it as simple as possible - simply a Remote object on the server with various methods that take Serializables as parameters and return Serializables.
Whether or not this is MVC depends on your interpretation. You could see the clients as views with the model and controller on the server in which case it is MVC with the event mechanism being a remote implementation of the observer pattern.
The trickiest part of the task will definitely be getting the code on the server that notifies the clients correct as it will need to be multi-threaded and handle errors gracefully - good luck!

Server-client Java distributed application

I have to design a distributed application composed by one server (developed in Java) and one or more remote GUI clients (Swing application with windows).
As stated before the clients are Swing GUI application that can connect to the server in order to receive and send data.
The communication is bidirectional (Server <=> Clients).
Data sent over the network is mainly composed by my domain logic objects.
Two brief examples: a client calls the server in order to receive data to populate a table inside a window; the server calls client in order to send data to refresh a specific widget (like a button).
The amount of data transmitted between server and clients and the frequency of the network calls are not particularly high.
Which technology do you suggest me for the server-clients communication?
I've in mind one technology suitable for me but I would like to know your opinions.
Thanks a lot.

The first technology that came to my mind was RMI - suitable if you're communicating between java client and java server. But you may get difficulties if you want do switch the client technology to - say - a webinterface.

I would go with RMI but implement the whole architecture using Spring framework. This way it is independent of technology used and can be switched to other ways of communication (such as HTTP or other ) with almost no coding.
UPDATE: And Spring will allow you to have none of RMI specific code.

I believe sockets should do the trick. They are flexible and not especially hard to code/maintain. Most entry level programmer should also be able to maintain them. They are also fast and adapt to any kind of environment.
Unless, your server is going to be off-site or you expect to have firewall issues. In that case, web services are the way to go since your basic communication happens through port 80.

I would second msparer's suggestion of RMI, except I would just use EJB3 (which uses RMI as the communication protocol). EJB3 are very easy and even if you don't use the other feaures EJB gives you (e.g., security) you can still leverage Container Managed Transactions (CMT). It really does make development easy.
As for the server->client communication, you would probably want to use JMS. Again, using EJB3 this is pretty e3asy to do with annotations. The clients will subscribe to the message service and receive update notifications from the server.
And yes, I am currently working on an application that does this very thing. Unfortunately we are using EJB2.1. Still, it is my opinion that this is where EJBs really shine. Using EJBs in a web app is frequently overkill, but in a distributed client/server app they work very well.

You can try using ICE http://www.zeroc.com for establishing server-client connection.