Building the Realtime User Experience

Server-Side Filters (with Java)

Our liveblog application will allow any number of clients to connect and view the content in realtime, but it also will allow any number of people to publish content. We don’t want to rely on the hope that the users will never find our content creation URL, so we’re going to have to lock it down. This is a great opportunity for us to test out some Java code. If you’re not familiar with Java, don’t worry. It won’t hurt a bit.

To limit posting access to authorized users, we’re going to require a password to be sent along with each publish request. If the password is correct, we’ll publish the content; if it’s wrong, we’ll silently ignore the request. On the server side we can check for this password in a number of places, but we’re going to do it from within the server-side content filter.

Server-side filters are Java-based classes that work very simply. As messages get sent to specific channels on the server, the server checks to see whether those channels have any filters set up. If a filter is configured, the request is sent to the filter before doing any other processing on the request. Inside the filter class, the data may be modified and returned to be operated on by the server or passed back to the clients. But if the filter returns null, the message is dropped and not delivered any further up the chain, and certainly not back to clients who have subscribed to the channel. This makes it a perfect place for us to check for the correct password. ...