Last week I created a new Java package named “net.gredler.app.converter” during a bit of refactoring. I know, I know. Pretty impressive stuff. But there’s more.
If you’ve used Eclipse before, you know that it provides feedback as you type, alerting you if your package name is not valid as is. For example, if you type “net.gredler.app.”, Eclipse will helpfully throw up the following error:
Invalid package name. A package name cannot start or end with a dot.
Well, I eventually got to “net.gredler.app.con”, and received the following error message:
Invalid package name. con is an invalid name on this platform.
Weird, no? It turns out that there are some limitations on directory names in Windows: you can’t have directories named “con”, “prn”, “aux” or “nul”, among others.
Apparently these were reserved words in DOS back in the day, and this restriction has propagated to the latest versions of Windows in the name of backward compatibility.
So if you’re coding in Linux or Mac OS X and want to ensure that your Java web application isn’t deployable on Windows, adding a package named “con” ought to do the trick (assuming your servlet container explodes WARs) 
