Recently we were trying to upgrade to the latest release of Java 5 (the J2SE05_04 version to be exact) so we could make use of the various bug fixes in the VM, and just to stay on the bleeding edge. After running our entire test suite (I could not imagine life without it!), we found that the URLConnection.connect() had a regression, throwing errors when you have a URL containing foreign characters such as éâäàåçêëÇèïîÄèïîÄ (basically anything after %8x through to %FF). Kudos has to be given to Ajit George who did all of the investigation work but does not have a blog to post this on.

For example:

URL foreignURL = new URL("http://java.sun.com/%80/");
URLConnection connection = foreignURL.openConnection();
connection.connect(); // IllegalArgumentException thrown here

We were lucky enough that only our test code exercised this API, but be warned if your application makes use of this and you upgrade to the latest version. A bug report for this can be found here. According to sun, the underlying class that is apparently the problem, sun.net.www.ParseUtil, has had this issue since the latest JDK1.4 version, but this regression appears when you use the URLConnection.connect() only in J2SE05_03 and the current release J2SE05_04 but works fine for J2SE05_02.