I just got started with Java Web Application Development and I've been developing a Web Application with Java Servelts using Apache Tomcat where customers can book appointments with hair stylists. Now I want to add a feature where stylists are notified by a push notification in real time once a client makes an appointment. I did my research and I found out the following ways:
Long Polling
Server Sent Events/ Event Source
Web Sockets
Since the necessary communication is asynchronous from the server, I feel that the Server Sent Events would be the right choice.
I came up with an idea where the book event generates a notification which is stored in a separate table. A thread monitors the data source for any new notifications and notifies the targeted receiver once a new nofication is found.
The issue I am facing here is how to identify the necessary active client out of several clients and target the data to it.
I've been looking everywhere in the internet and I couldn't find any Java Servlet and Tomcat implementations for reference.
Is it possible to implement my idea using just Servlets in a Tomcat container?
If there is a better approach to this problem, please let me know.
Related
I'm building a website using springboot as RestAPI and angular in frontend. Also, i will be getting data in my rest(consumer) from around 40-50 swing standalone apps(producers) through kafka. I need to implement online status for those swing apps. Basically, i need to know when and which one of swing apps went offline or back online. Is there a way to implement this? If this is impossible with kafka can you recommend something else for communication?
Clarification:
By online status i mean whether device on which swing app is installed has internet connection or not.
Swing app will be installed on around 40-50 devices on remote locations.
Eventually i got rid of kafka and used websockets. Using WebSocketHandler i had information when certain standalone app is connected or disconnected. When standalone app looses internet connection server is notified relatively quickly (within 60 seconds). Keep in mind that in my case standalone app will be sending data quite often. If this is not the case for you then i recommend looking for some other solutions and taking a look at #OneCriketeer comment regarding Nagios.
I am creating an app using React-Native for the front-end, Java for the back-end and PostgreSQL for the database.
One feature of this app is to allow users to add each other as friends and instant message them - just like other social networks. At the moment, security is not a priority but I don't want to create something that I will have to completely redo when I do have to make it secure!
The goal here is to give each user the ability to send/receive messages to/from their friends. They also need to be able to view the message history with each contact.
I just need some advice on the following points to get me going as I haven't gotten very far on my own:
How should I send messages from the front-end, to the Java server and then to the receiver? This will involve the app having to listen for new messages so would the Socket.IO library be the way to go for this?
How I should store the messages in the database? E.g. have a table for messages with user_ids to be used for retrieval?
I should point out that I am very new to React-Native, databases and networking so I am finding this very challenging!
I will massively appreciate any help and any examples would be fantastic!
You should use WebSocket on the server. Spring supports it
Here's a tutorial I wrote about sending messages from PostgreSQL to the browser using WebSocket, which isn't exactly what you're going to do, but can hopefully get you started:
http://blog.databasepatterns.com/2014/04/postgresql-nofify-websocket-spring-mvc.html
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
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.
I'm implementing a client-server GPS application. Client side is a J2ME midlet that sends GPS location via HTTP/XML to a Java Webservice (Tomcat servlet). The servlet stores positions in SQL database. The other client app is a web browser that can login and see the actual position of midlet using Google Maps. This client is written using GWT. All is deployed on the same Tomcat container. Now I'm wondering how to dynamically update current position in webrowser Google Maps of the mobile so that the client can see how the mobile moves. How to do it in GWT - should I create a timer object in GWT client and asynchronously send HTTP request to server for getting the actual positions? Or is there any mechanism in AJAX/GWT to notify client (web browser) about the data update?
Thanks
Dominik
Regardless of all the talk about "push", the standard HTTP model is still one where the client has to ask the server for updates.
In a GWT app, you should use the well-supported Ajax functionality to request small-granular updates (polling, I guess) from the server at regular intervals (5 seconds, maybe?) and use the newly obtained information to update your map info.
There is a detailed article on the GWT incubator web site about Server Push and how to achieve it with GWT. From the article:
Explains Server Push, sometimes known as 'comet', and how you can achieve this with GWT.
Then, if you take a look at the comments, you can find interested related information and open implementations as gwt-comet, GWTEventService ...
I agree with rok.
If your deployment is going to be small enough to be able to support one permanent connection per web browser client go with Server Push/ Hanging RPC/ Long Polling or whatever you want to call it.