i would like to know how the update messages in this stack overflow site have been implemented.
To be more precise, for example while i am trying to reply for question and i am in the middle of typing my response, i will see a message on top of the page saying a new answer has been added. How is this feature has been implemented.
AFAIK, the possible way can be HTML5 websocket or serversocket technology.
is there any other way to achieve this kind of push notification system especially using java, spring and jquery environment?
Not sure how to tag this question. correct the tags if i am wrong.
SO uses reverse ajax/comet technology to show those messages. I remember reading some discussion on meta about this feature, couldn't exactly find out the link for it at this moment. Will update as soon as I find.
Based on programming language framework name may change (websockets (or) socket.io etc.,), but at the end they all are from comet framework.
Update:
Here is SO meta discussion on this topic.
I have used the Direct Web Remoting framework with success. (DWR).
There are several ways to achieve that:
Polling: using JQuery you issue a request regularly (every 5sec for examples) which retrieves the updates from the server.
Streaming: you issue a request, the server does not set a Content-Length to the response and "never" close the socket. This way you can send data from server to client whenever you want. But it means that for every client a connection is hold by your server.
Long polling: mix between the two previous ways. The connection is hold by the server but with a timeout. If no new data is available, the server closes the connection and the client reopen a new one after a moment.
Thoses are Push technologies: http://en.wikipedia.org/wiki/Push_technology
Of course there are over ways to achieve that.
Related
I need to create an app which get's it's displayed data from FIX protocol in real time.
How would be best practice to accomplish this?
Should the mobile app read directly the FIX data?
Should I put a server in between to transform the FIX data to JSON or something more prepared for service consumption? And if so... how would I do it to not lose the real time? Creating a websocket in Java which for the mobile apps to call and that websocket would transform the FIX data to JSON that way?
I never worked with the FIX protocol before by the way.
So like, the question is, can you put a FIX client on a mobile phone? I guess you can, and I am sure it will happen soon.
Yes, anything can read FIX data, it's simply text stream name value pairs, where the name is a numbered tag to identify some particular financial data or process, as agreed between the FIX community as a whole, or between direct counterparties using messaging data dictionaries.
These days you could try using SBE throughout, including at the mobile client, but for now current practise is yes, to use JSON for client endpoints (where the JSON name is not a FIX tag but the underlying FIX field name so it's easier for people to understand) and pass JSON messages to the mobile device in some kind of REST data processing.
So yeah, you'd have a FIX server (if you are new to FIX try QuickFix) to connect with your provider. Then what you need between that server and mobile clients is asynchronous messaging. Consider a quote request is not a simple request / response where you can block the request thread until a single response is received, it's a request followed by a stream of many responses. So you want an event handler style to route the responses back to clients asynchronously. With many mobile UI clients making requests and receiving responses you need to demultiplex the responses from the 1 FIX server out to the many mobile clients. That's something that QuickFIX itself kind of already does using a session layer. You need to do the same using sessions or identifiers in the messages you're passing around.
Yeah I guess websockets are intended to be that solution for real time. You could write a native mobile app though, using something like node or react to handle the message events.
So I'm trying to write an executable JAR for a small subreddit I run.
I have a post that Jsoup connects to and reads all the URLs on that page. In another method, it then connects to all those URLs (that are just comments on the post) and gets the HTML from the comments and saves them to a HashMap.
This is great however I am getting a 429 HTTP Error. So to resolve this, I added a short 5 second wait. Now I'm getting a SocketTimeoutException "Read timed out". Once I lowered the time down to 3 seconds, I was bouncing between the two.
Now I run a few Reddit bots with Python and I'm able to make a lot more requests than what I'm doing here. I actually have a single bot that makes thousands of requests every minute. So I know it's possible to make these requests.
My question essentially is, how am I able to make multiple requests to Reddit and avoid the 429 HTTP Error? I'm using Jsoup to connect and read the HTML.
While I'm sure connecting to Reddit via. their OAuth2 API will fix the issues, I have no idea how to actually use OAuth2 in Java (I actually use a wrapper in Python so it's fair to say I don't know at all) and I don't know how to then use that with Jsoup.
My question essentially is, how am I able to make multiple requests to Reddit and avoid the 429 HTTP Error?
You answer this yourself:
While I'm sure connecting to Reddit via. their OAuth2 API will fix the issues,
As specified in the API documentation, you get twice as many requests per second if authenticated using OAuth.
Have you looked around for examples on how to handle OAuth flows in Java?
You might also find it easier to use one of the wrapper libraries for Java, instead of handling all this yourself.
Just set header and you can easily pass it
User-Agent: super happy flair bot by /u/spladug
I am doing an app which renders a web page in an upnp enabled television set. I have implemented the UPnP with Cling UPnP
Now I am not sure how to proceed further. How is the connection between the Television and the device attained? Is it a socket connection? has anybody got any samples or tutorials regarding this topic which help me to implement UPnP streaming.
I have searched on google but it mainly points to existing apps available in google play.
Thanks
Ok, so the service descriptor xml (SCPD) contains <actionList> of <action>s with their parameters, which can be in (to the TV) or out (will be in the TV's response to the action). You need to "call" the action, which means that Cling serializes it to SOAP RPC and sends it to the device as HTTP request. In the response, you will get the overall result of the call as with plain HTTP, 200 for OK, 500 for Bad Request, etc. Each code has a specific explanation in context of the particular action call. The response will also hold out parameters as specified in the SCPD.
But this all is not as much of your interest when using an abstraction library like Cling. It will do everything for you. Disclaimer: i am not familiar with Cling, just with enough other UPnP libs to know where to look for things.
As a TV set, the 3 services you mention will be undoubtely AVTransport,ConnectionManager and RenderingControl. So to present a simple example which will actually do something observable on the TV, let's call RenderingControl.SetVolume. The method you need is org.teleal.cling.support.renderingcontrol.callback.SetVolume. I can't help you to the level of knowing where to obtain the Service parameter, but you should be able to figure out.
I am not saying that you don't need to know how UPnP works under the hood. Grabbing the UPnP specs bundle and reading at least the DeviceArchitecture pdf is indispensable. And you will definitely need the specs to understand the more complicated services like AVTransport. Hint: don't care about InstanceID and ConnectionID. It's all 0 unless you connect to a very advanced renderer (which the TVs nowadays are not).
This question already has answers here:
Real time updates from database using JSF/Java EE
(3 answers)
Closed 2 years ago.
The backend of my web application receives updates from several clients. When such an update happens it should be communicated to all other clients.
How can I initiate an update from the server to all web browser clients when my backend is updated?
I'm using JBoss, JSF and the Spring framework.
See similar Stack overflow quetion : WebSockets vs. Server-Sent events/EventSource
I'm assuming, as DarthVader did, that your frontend is a (generally) stateless HTML page of some sort. Something in a browser. If you want all clients to be pushed changes automatically, you have three options:
Comet: (deprecated)
Comet is essentially making AJAX requests that have no request timeout limit. You make the request, and it sits there and streams data through it as is neccessary. This can be done with hidden iFrames or standard XMLHTTPRequests (which jQuery can wrap for you). You can read more about this method here.
Long Polling:
Essentially, you use the javascript setInterval method to continuously poll your server for changes. Simply set an interval that does a standard AJAX GET request to the server, and upon every success, update your page accordingly.
Browser APIs
HTML5 WebSockets
Using any type of Event-Based backend (Twisted, EventMachine, node.js, etc) makes WebSockets the ideal solution. Simply have all clients register with the backend, and upon a submit from any given client, push the changes to all other clients. You can read more (and see a nice example) of WebSockets on this page. Browser support => canIuse
Server-sent event (SSE)
With server-sent events, it's possible for a server to send new data to a web page at any time, by pushing messages to the web page. These incoming messages can be treated as Events + data inside the web page.
Browser suppport => canIuse
When you say front end, you are talking about stateless http client.
You cant push anything from your web servers to http or stateless clients.
The "trick" to do this if using asynchronous calls from front end to your back end, periodically.
Think about gmail, how do you think it displays that you have an email when you recieve a new email. You browser contantly, sending Asynch calls to gmail servers, if and when there is a new message, it displays it.
So Clients are stateless. use Ajax.
is this clear?
There are a couple of ways to go around this.. The way it should be in the future is following standards like Websockets
For now you are stuck with Comet which is essentially sending a request to the server and keeping it open (not signaling a response end) and just streaming data through it (Parking the request they call it). Or periodic polling, where you just do an AJAX request to the server every predefined interval to ask if the server has something new to say. Needless to say the first work around requires streaming support on both the server and browser but is more efficient in most scenarios.
I a deveveloping a web site that comunicates with a custom made webserver by me in Java. The web site is made in PHP/JavaScript/JQuery running on Apache and i made a simple second webserver in Java to support some designed features by me, and this server runs under another port XXXXX. The problem is, i want to make requests in jQuery to second server the domain is diferent, the page runs on domain and the $.getJSON function calls domain:XXXXX wich is not allowed. I thought user $.getJSONP but im concerning concerned issues. The connections between two points is authed (i was think by passing a token beyond the callback generated by jquery). The two poins are supported by. Is there safe in this case use $.getJSONP or exists other alternatives thinking in browsers support(IE7+ and FF3+).
Sorry for my english :)
Best regards lealoureiro
JSONP should work for your needs, however your other option would be to have a proxy service on your second server that would make the request server side. Your client-side code could then access all the data natively via json instead of jsonp.