Java.net maven repository outage
Java.net maven repositories have been offline throughout yesterday, but they are back now. Sorry for the trouble it caused.
There was a bug in Maven that made this outage worse, too. Once in a while, maven checks the updates to plugins by talking to the remote repository. And when it fails to connect (like in this case, because the server was out), it clobbers the maven-metadata.xml entirely, and it ends up making your local versions unusable.
And once this happens, retrying with the -o option do you no good.
As a result of this, despite the fact that many people had all the relevant versions of artifacts they needed to do a build, projects become non-buildable nontheless during the outage.