This questions was asked during one of the interview. How to transfer data from one server to another using AJAX? Is it really possible?
AJAX is generally used on the client side, not usually the server side.
It sends requests to a server.
You probably need to provide more information about what you are trying to achieve to get a decent answer.
If you are wanting to transfer data from a "client" to a server then you could send the data in a variety of ways - especially with AJAX. Just how depends on what data type and size. Requests from a client to server (HTTP) can include POST data, which can carry your data to the server.
If you are using AJAX on a client and wanting to use it to transfer data from one remote server to another then you could get AJAX on your client to call a script on the server that would instigate the transfer from the server to another server in some way. (such as FTP or SCP maybe - or even using a server to server HTTP POST)
If you can be a little more specific about what you need to do then I will try and give you a better answer.
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I am a beginner in web and server side development and have just read about Ajax. It is used on client side to access any resource over the internet.
But I am thinking of some utility on the server side as ajax so that server is able to send request to the client and client responds to the request.
Do you people know how to achieve this? Basically what I want to achieve is that I have a server which sends the curent server time to the connected client each second.
Thank you!
This can be achieved with websockets.
In .NET we use SignalR to achieve what you need. Server sends a message and client replies to it. This is pubsub scenario.
https://hackernoon.com/create-your-own-pubsub-client-server-use-websocket-65dd1820e997
I have a Client that tell my server to contact another server and save the data there upon saving if successful I can receive a callback, how can I then tell the Client to refresh the page because this 2nd Server is also sending data to the Client, can I do it using headers?
There is no tranditional ways to push messages (refresh request and so on) to the webpage directly from the server.
Before giving some solutions, I'm sorry to say that your description to your question is quite ambiguous. server, another server, this 2nd Server is also sending data to the Client does not make much sense. You may reorganize your description to show the whole business logic better. Giving necessary code will be better.
So focusing on sending message from server to client within browser environment, there are several ways you could consider:
Ajax
You could use ajax to request the server at client side. You can poll the server at regular intervals, checking the response to determine whether the page should be refreshed.
Pro: widely supported, easy for both client side and server side
Con: polling is not a real-time solution and will make some redundant requests
Websocket
Pro: real-time bidirectional socket-like communication
Con: may be too heavy for the simple task you mentioned
Server push
Part of PWA specification
Pro: allow direct communication from server to client
Con: complexity, insufficient browser support
Is there any way in spring where I can POST the requests to another domain from My controller? I have parameters which I need to pass in POST from the controller to another third party domain, is this possible?
What you probably want is for your server to act like a HTTP client and send some data via HTTP POST to a third server:
Your web app client ---> Your web server ---> Another web server
If that is indeed what you need, yes, it is possible. The fact that your application is a web server itself isn't important, although it can be confusing - it's easier to think about it as if you wanted to post the data from an ordinary command-line Java application.
One of the many tools that can help you is Apache HttpClient.
I have an intranet based CRM application developed in CodeIgniter 2.1 where the application is running on a local Apache server and around 20 clients are accessing it over LAN. This is to be connected to a call center setup where the call center application (running on a separate server) will do a HTTP post with caller's number as well as terminal number of the agent where the call is arriving to a URL of my Codeigniter application. I am using this data to populate a database table of call records.
Now from the terminal number (each terminal has static IP, and a session in Codeigniter is linked to IP as well) I can find out which user (login session) of my application is about to receive the call. I want to find a way out how I can send data from server side (it will be regarding the call like the number who is calling, past call records etc.) to that specific user's browser via AJAX or something similar? The agent's browser needs to display this information sent from server.
Periodic polling from browser by jquery etc. is not possible as the data needs to be updated almost instantaneously and rapid polling up to this extent will lead to high CPU usage at client end as well as extra load on network.
P.S.: I only want to know how to modify the browser data from server end.
In AJAX, asynchronous request/response doesn't involve polling; there's just an open TCP connection and non-blocking I/O. The client makes a request but returns immediately; when the server sends the response, the client is notified. So you can achieve what you want with AJAX's XMLHttpRequest without polling[1]. All you need is a url from which to serve your notifications. You could have one request thread and a general dispatch method, or different urls and different threads for each, depending on how you needed to scale.
[1] Well, to be honest, with very little polling. You'd really need to establish what the session/global timeout was and reissue requests within that time limit.
I've developed a web-based application in which a signed in user should send a message to the server telling he is still online every 3 seconds. The message is then processed by the server and a stored procedure is called in Mysql to set the user's status to online.
I've looked in to similar issues in which Comet and Ajax are compared (here or here) but considering that 3 second delay is acceptable and maximum users of 1000 are online in the system, is using Ajax a wise choice or Comet should be used?
For this kind of feature comet is more appropriate:
Your clients send messages (i'm online)
Your server broadcast the processed message (user X is still online)
In an ajax way you are only serving messages to server.
In order to get the "broadcast effect" in an ajax way. You will end up doing something similar to comet but with less efficient bandwidth.
Ajax:
Client send server - i'm in
Server process
Server send back to client list of user in.
In this case every client ask every 3 second the database for the COMPLETE "in" list.
In comet:
Client X send server - i'm in
Server process
Server send back to client S that user X is still online
In this case every client tell the server every 3 second that he is in.
The server send back to every connected client ONLY that x is still in
Comet is just the technique to broadcast back and push messages to client
Ajax is the technique to push client information to the server without having to refresh all the page.
Quoting wikipedia:
http://en.wikipedia.org/wiki/Comet_%28programming%29
Comet is known by several other names, including Ajax Push, Reverse Ajax , Two-way-web, HTTP Streaming,and HTTP server push among others.
So go comet :)
If you do not broadcast anything, then simple Ajax is the best option
In this particular case, since you do not need to send any information from the server to the client(s), I believe Ajax is the more appropriate solution. Every three seconds, the client tells the server it is connected, the database is updated, and you're done.
It could certainly be done using Comet, in which case you would basically ping each registered client to see if it is still connected. But, you would still need to run a query on the database for each client that responds, plus you would still need the client to notify the server on its initial connection. So, it seems to me that Comet would be more trouble than it's worth. The only thing that might make sense is if you could ping each registered client and store the responses in memory, then once all clients have been pinged you can run one single query to update all of their statuses. This would give you the added bonus of knowing as soon as a client disconnects as opposed to waiting for a timeout. Unfortunately, that is beyond the scope of my expertise with Comet so, at this point, I can't help to actually implement it.