I have a Java Play Framework 2.5 project where periodically I have to update the registries of our customer. I can't do a simple SQL insert/update because I to do some logic and operation on every single row.
I ended up uploading on my website an xlsx file (asynchronous way) with JS and then working on it with Apache POI.
My only problem is that I don't know how to inform the user who uploaded the file on the progress of the processing of the file.
I'll like to simple show every 10% a message with the percentage.
I've searched on the net, I think the best way is to use websockets with Akka (BroadcastHub), but i'm only finding examples in Scala or for 2-way communication that send output only when an input is received.
If you know a different way to do it you are welcome!
I suggest you look at https://github.com/playframework/play-java-websocket-example : It gives an example of a websocket and an actor interaction.
In your case, you would create a named actor (useractor-someid), which manages the mutations. The controller then would reference the same actor (or have an other actor send to useractor-someid), so that it can fetch the status. I suggest you use a JsonNode flow, so you can send / receive JSON in the websocket connection.
Related
I have the most basic problem ever. The user wants to export some data which is around 20-70k records and can take from 20-40 seconds to execute and the file can be around 5-15MB.
Currently my code is as such:
User clicks a button which makes an API call to a Java Lambda
AWS Lambda Handler calls a method to get the data from DB and generate excel file using Apache POI
Set Response Headers and send the file as XLSX in the response body
I am now faced with two bottlenecks:
API Gateway times out after 29 seconds; if file takes longer to
generate it will not work and user get 504 in the browser
Response from lambda can only be 6MB, if file is bigger the user will
get 413/502 in the browser
What should be my approach to just download A GENERATED RUNTIME file (not pre-built in s3) using AWS?
If you want to keep it simple (no additional queues or async processing) this is what I'd recommend to overcome the two limitations you describe:
Use the new AWS Lambda Endpoints. Since that option doesn't use the AWS API Gateway, you shouldn't be restricted to the 29-sec timeout (not 100% sure about this).
Write the file to S3, then get a temporary presigned URL to the file and return a redirect (HTTP 302) to the client. This way you won't be restricted to the 6MB response size.
Here are the possible options for you.
Use Javascript skills to rescue. Accept the request from browser/client and immediately respond from server that your file preparation is in progress. Meanwhile continue preparing the file in the background (sperate job). Using java script, keep polling the status of file using separate request. Once the file is ready return it back.
Smarter front-end clients use web-sockets to solve such problems.
In case DB query is the culprit, cache the data on server side, if possible, for you.
When your script takes more than 30s to run on your server then you implement queues, you can get help from this tutorial on how to implement queues using SQS or any other service.
https://mikecroft.io/2018/04/09/use-aws-lambda-to-send-to-sqs.html
Once you implement queues your timeout issue will be solved because now you are fetching your big data records in the background thread on your server.
Once the excel file is ready in the background then you have to save it in your s3 bucket or hard disk on your server and create a downloadable link for your user.
Once the download link is created you will send that to your user via email. In this case, you should have your user email.
So the summary is Apply queue -> send a mail with the downloadable file.
Instead of some sophisticated solution (though that would be interesting).
Inventory. You will split the Excel in portions of say 10 k rows. Calculate the number of docs.
For every Excel generation called you have a reduced work load.
Whether e-mail, page with links, using a queue you decide.
The advantage is staying below e-mail limits, response time-outs, denial of service.
(In Excel one could also create a master document, but I have no experience.)
I'm trying to make a simple tic-tac-toe online multiplayer game in Play Framework in Java (but I can read Scala too) and I need to notify one client when the other client has made a move - has inserted a new database entry. The frontend uses HTML and JS.
Do I use WebSockets or Server Sent Events for this and how?
Thanks a lot guys, the Play framework documentation for both is still not updated and it's a well known issue https://github.com/playframework/playframework/issues/5057 as well.
EDIT: The main question here is really how to do it?
Personally for a game I would establish a Web Socket connection over a SSE.
Fast data transfers
A two way stream of message, where SSE would require the client to send ajax requests and listen to SSE where WS all sits in one place.
Allows you to establish when one of the 2 clients looses connections, thus pausing or notifying the other player.
Resource you can use to Implement this:
https://www.playframework.com/documentation/2.5.x/ScalaWebSockets
Edit: Latest version https://www.playframework.com/documentation/2.6.x/ScalaWebSockets
My setup consists of a Weblogic server that runs various REST services that accepts an HTTP request from a client(an android app), reads data from a MySql database and sends this data as a response to the client.
My requirement is that the client should be notified as soon as the database is updated. I have implemented a "polling" mechanism. The client constantly sends requests and checks for any changes made in the database. However this is not a very efficient mechanism.
Can you please suggest any efficient ways of achieving this?
Thanks in advance!
One of the way to use writing a CRON job for observation of Database change.
also, SO has already discussed this topic. refer below link,
Oracle database to send notification / Invoke a java method on reaching Time specified in a column
I'm building an Android app in which I want to display some real time data (updated every second) which I want to stream directly from my server to the App. There will be multiple Apps connected at the same time, which should all get the same stream. I am now looking for a way to do this from both the server and the client/Android side. From the server side I can basically build anything, so I thought I'd start from the client side.
In the Android docs I found the inputStream class which I guess is what I need for this. So my first question: is the inputStream class the right tool for the job?
If so, I guess I can set it up (found some examples on the net), but from here I'm still unsure of how to build this service from the server side? Do I need to build a simple page which I constantly update, or should I use a messaging lib such as zeromq with multicasting? Any more tips/hints/pointers on which technology to use for the server side would be very welcome as well!
This depends on your data. For example if you need to keep your clients updated on some values, like weather data in a location, a simple polling mechanism will suffice. You would have to build a web page that shows the current values and the clients would have to keep polling and parsing the page in the time intervals desired.
On the other hand, if you've got a stream of binary data that need to be transferred to the client, you would need to do some socket programming. There are tons of samples like this to help you get started. Also keep in mind that to maintain your sockets with the server, you will have to keep them running in the background as a service.
I think I'm just missing a little detail that is preventing me from seeing the whole picture.
I have a web application which use ajax request every x time to update client with new information or tasks.
I also have a long running process on the server which is a java computation engine. I would like this engine to send update to the client.
I am wondering how to migrate my web app to using websocket. Probably phpwebsocket or similar. Can my server 'decide' to send information to a specific client? It seems possible looking at the php-websocket.
Can my java backend long process use the websocket server to send notification to a specific client. How? well I can say that my java app could use a class that could send over websocket instead of http.
But how the websocket server knows to which client to send the 'info'. I am puzzle by all this. Any document that explain this in more details? It seems that the websocket could create an instance of my web application.
Thanks
Your server, which will have an arbitrary number of active client sockets, decides which ones to write to (possibly in response to input from the user).
phpwebsocket (which is still very rough around the edges) has a User class with $id, $socket (this is the underlying TCP socket), and $handshake fields. You could extend that class with additional metadata about the User (e.g. a computation identifier). Or you could use an array mapping from computation id to User.
Perhaps when Java computation n finishes, you can look up the socket associated with that computation, and write to its socket.