Distributed web service. What technology to use?

Question

Hi all,
I need advice on what technology, architecture and platforms to use for the following:
I have 1 thousand remote clients. These clients must receive notifications from my server on certain events that happen specific to that client.
I would like to create a web based application that the client can log into and then whenever the specific event occurs it must show on his/her screen - I don't want the web page to refresh every 10 seconds and check a database (or some variable on the server) to check for the event. I want the server to send a message to that persons browser notifying them of the event.
What is the best way to do this?
Regards,

Answer 1

Sounds like applets would do the job. Will require installation of the JRE on clients.
One problem: applets can open socket connections only to the computer from which they were loaded. Unless you sign them. If there is a web server sitting at port 80, where do you put the push server... A hack is to use port 443 (HTTPS) for the push. 80 and 443 are probably most often open in firewalls.
If a user has a proxying firewall no push scheme will get through. There may be other push-unfriendly firewall schemes too, such as forcefully closing all connections after a few minutes' timeout.
Also - If I could have a java app/applet on the client's machine -
what is best practice to maintain a thousand connections if I
use sockets? (usually I spawn a thread for new sockets, but
I surely can't do that with 1000 clients?)1000 threads is indeed a bit on the high side. If the client never sends anything back you could simply not read from the sockets in the server. No need for per-client threads then. If you need to read use a NIO selector. I'd probably code a selector even if I didn't need to read from the clients, just for cleanliness.