Purpose:
I'm trying to make a real-time web service in Java. When there're changes in database, the data in clients(probably Android client) will be changed automatically without refreshing.
Platform:
I'm using Tomcat 7 container and Axis2.
Problems:
I'm stuck in the way to approach. I've realized that there were 2 ways:
1. When the data in server changes, notice to all the clients. Web-service allows us to do this, but I don't know what clients I have to inform!
2. Clients connect to the server, keep the connection alive and whenever there's a change, update data. However, if the client is the handheld, it will consume much power and data exchange over 3G network.
I know that's a complicated problem. So I just want to ask if there is an efficient way to approach? And if possible, anyone can give me one example of realtime web service like this?
I've searched over many pages, but nothing's helpful. Can anyone give me some suggestions? Tkx!
Is it a requirement to use webservices or Axis? Otherwise, you might be interested in WebSockets. These are connections over plain HTTP that provide two way communication. Your clients will connect to your server, and as soon as new data is available your server can push data to every connection it knows of, thus informing all clients that are connected.
Related
I want to monitor firebase client connections from my java server.
I have found a lot of examples on how to use onDisconnect from the client side (iOS), and it works great.
But is it possible to monitor client connections from a java server using the java server sdk? I simply want my server to know about user disconnects, but without the client having to 'tell' the firebase database that it has connected/disconnected.
The reason for this is mostly security, and a wish to trust the client as little as possible to do important tasks. Ideally most of my data should be 'read only' from the client, except for some 'write only' request queues consumed by the java server.
From the firebase java server documentation: https://firebase.google.com/docs/reference/serverreference/com/google/firebase/database/OnDisconnect
The OnDisconnect class is used to manage operations that will be run
on the server when this client disconnects. It can be used to add or
remove data based on a client's connection status. It is very useful
in applications looking for 'presence' functionality.
It seems like what I want to do is possible and supported, but I'm having a hard time figuring out how to make my server monitor 100-1000 connections realtime.
Lets say I'm monitoring a database reference that I know clients are monitoring. In that case none of the options to 'remove on disconnect' or to 'set on disconnect' are useful.
Thanks a lot for reading this, I'm REALLY loving firebase right now, just a few more issues to figure out :-) Also sorry for my english, I'm not a native speaker.
I've been through different questions about this topic, however, none of them have cleared my doubts on the best approach notifying the client side of a server-client IM app.
The Problem:
The whole problem is how to notify the client application of updates. I've alread seen the following approaches:
Clients keeps checking for updates: From time to time, client app performs a check in the server to see if there are updates for that specific user;
Problem: it is not performatic at all. Suppose you have one million users and each one of them checks for new updates every second. Serve would have to deal with one million requests per second. Wont work.
Client app opens a socket: The client app opens a socket and sends its address to the server. Server, by its turn, persists this information and connects to the socket whenever it needs to notify the client of some update.
Problem: Often the client will be connected to a NAT, so, the IP it has access to is in a non-visible range. In order to send messages to this client, a port forwarding in the NAT would have to be configured, which can't be done.
Despite of the technology, I think this approach will always be used, however, I have no idea how the problem described above can be solved.
Google Cloud Message (GCM): use the GCM service to notify the client of any update. Problem: It does't seems right to use a third server to handle the IM and it raises concerns about the scalability of the system. When the number of messages and users increases exponentially, it seems that the service will go down. Despite that, it seems that passing the information for two servers before delivering to the targets just adds bottlenecks in the process.
A combination of 2 and 3: uses GCM to reach the client when the last persist addres is no longer available.
Problem: same as described in 2
XMPP: I've seen many answers indicating the use of XMPP for IM applications, however, XMPP is a protocol - as per what I've foun in the web. I don't see how it can solve the problem described in 2 for instance.
Given the options above, can someone indicate me what line should I try to go for? Which one of these approaches has the best chances of success?
Thank y'all in advanced.
Use Google Cloud Messaging. Opposing to what you stated this service is built to scale to billions of users it will generally not introduce performance bottlenecks.
What you basically want to do is to use the messaging service to wake up devices. If you insist you can then still use your client server approach and thus your own protocol to have the client lookup new messages from the backend.
After a lot of research i am more confused then before on what kind of server to use for an android app.
My question in a nutshell is: which kind of server is easier to use and deploy.
I want to create an android application that communicates with a server to find other clients, the server uses GCM to notify other clients that one client wants to communicate and is used to exchange the address of the clients. Afterwards the clients should be able to communicate directly to one another.
What i found out is that from the android point of view either would be fine, both is likewise possible and neither produces more work then the other.
On the server side it looks like web service would be better to use, because it is easier to find a server provider. I might be wrong here but it looks like most large server providers don't like to give you enough access to run a jar file.
Google and amazon offer servers that can host web services, i am not sure if a socket server would be possible there, so if anyone can give me some tips on good and affordable server providers i would also like to have some insight there.
I need to write an application in java which communicates with a web server.
I know how to do that, using PHP, but I'm afraid it won't cut it in this one.
Here's my situation.
I have multiple clients, when one of them sends a specific message to the server (so far, no problem on PHP), I want it to send a certain message to all other connected clients.
The problem is, I could hardly find any information regarding server socket in PHP, which led me to believe this isn't the proper way of achieving that. I'm using a paid hosting (x10premium) to host my servers so far, so I was thinking of doing it with this one, however, I'm not sure it's even possible with PHP.
At the moment I'm having each of the clients periodically check with the server if he received a message from any of the other clients, but I don't like this solution...
I hope someone could point me to the right direction. I don't know too much about Ruby and other languages which are used to do stuff like that, But if necessary, I would gladly learn it.
Thanks in advance
EDIT:
Forgot to mention, the server (currently the PHP) would also communicate with a MySQL table. If it matters.
This is a good example of PHP socket server/client:
http://tech.navarr.me/2010/07/how-to-create-a-socket-server-in-php.html
You could do it just like with JAVA, but remember that PHP does not support multithreading or multiprocessing so if 10 clients connect at once to your server, you will process them one by one, so eventually 1 will have to wait for the other 9 to finish - everything, database and connection overhead.
If you do it with JAVA or Python for example, you could handle each request in separate thread so that DB & Network communication overhead is handled simultaneosly.
Python has build in socket server components and nice and easy to use mysql component, that would make it a breez to achieve this, without even having to understand threading at all.
For the python socket server see here:
http://docs.python.org/library/socketserver.html
Basically you just define a function that will be executed for each new client connection and tell the server to serve_forever() - until it dies, it will do what you want.
I am developing a chat website using jsp/servlet.I will be hosting my website on gooogle appengine .Now i have some doubts regarding whether to use server push or client pull technology
1)If i use server push and if i dont close the response of servlet will it cause the server to go slow?How many simultanious connection can a tyicall tomcat server can handle if i keep the socket open for the entire chat session between 2 clinets??
2)Will server push or clinet push be better??
If you are using a servlet (prior to 3.0), then I guess you'll have to go with pull because of the programming model of servlet. However, there ARE advantages in using a push model. Primarily, wasted load on server and the limitation in latency. That's why there are technologies such as comet. Servlet 3.0 also supports push model. These are commonly used in ajax based apps.
In fact I believe a push model is more suited for a chatting app. because of the fast response time (=better user experience) it can provide.
If you use a nio based implementation for push-model, you can support thousands or even more than 10k concurrent connections (obviously, your millage varies).
If you use a conventional IO based implementation, it will be likely in the range of hundreds of concurrent connections (don't take this estimation too seriously though. I'm just giving these numbers to give a very, very rough feeling).
As for tomcat, last time I checked, people were saying that it won't have a good push-model support until version 7.0. But I'm not following the current status so I'm not sure (Sorry, perhaps somebody else can help you on this). If that is the case, you might want to check out comet support of jetty.
grizzly and netty are also good NIO based network frameworks, but if you want to use JSP, and find that tomcat is not sufficient, I guess jetty would be the best bet.
edit: (some additional info)
In this "push models", it's not like the server opens a connection to the client. The connection will be kept alive, and the server will push messages as it sees fit.
Also, it's not like there are only "push" and "pull" models. You can have a hybrid, like long polling.
I don't know how are you thinking of achieving server push here. As far as I can see, server needs a request to respond over HTTP. So, when there is a request, server will respond to that.
If i use server push and if i dont close the response of servlet will it cause the server to go slow?
App Engine will not let you do that. You have to finish your response within thirty seconds, or it will be killed. The thirty seconds is also an edge case, most calculations they do (for quota and such) are based on a 75 millisecond response time.
How many simultanious connection can a tyicall tomcat server
Tomcat? I thought you are planning to use App Engine?
Pull. Always pull.
I know it's a manufacturing-oriented book but the advice from Lean Thinking (Womack & Jones) is invaluable in any context (roughly, from memory):
Start by defining value,
line up the activities that create value in the value-stream,
create flow across the value-stream,
let customers pull value from the value-stream,
compete against perfection rather than other organizations
If I misquoted them, I apologize. Anyway, all of those principles can easily be applied in the development of any software product just as they could in the production of any physical product but the one that matters for you is pull.
Letting consumers of a service pull rather than pushing to them not only makes your programming model easier, it aligns activity with demand. You can still use queuing to load-level over time, if you have to, just the way you could with push but, this way, you have complete visibility into what, exactly happens in any given transaction.
I don't quite get your first question but the answer is still pull.
The answer to your query depends on what underlying protocol you wish to use.
Since you have mentioned JSP/servlets, your app will be implemented over the HTTP protocol.
HTTP is a protocol over TCP. TCP is connection oriented and remains alive, until the connection is ended. However, HTTP connections are persistent, only for the duration of a single request-response cycle. The TCP connection is broken after every request-response cycle. So that should answer your doubt with regards to how many socket connections a typical TOMCAT server will be able to handle. The connections will not be persistent, at all. They will only last the duration of a HTTP request-response cycle.
Given this basic idea, I would suggest , you use a client pull strategy, to implement your app.
Even with server push, over HTTP, even though the name says "server push", it is always the web client that polls the server at regular intervals, which just gives an illusion of "server-push". HTTP specification mandates that the client makes a request to which the server responds.
I have considerable experience in developing chat applications (both mobile and web).
Let me know , if you need any assistance. I will be more that willing to help.