Presumably you know about File.renameTo(), right? It's just one file at a time, but you can always write a loop. The bigger headache is remembering to check the return value, and if it's false, figuring out why. I hate those methods that return a boolean with no useful diagnostic message if a failure occurs - File has several of these.
Jakarta Commons IO has an assortment of methods that fix some of these problems, e.g. FileUtils.forceDelete() and FileUtils.forceMkDir(), but there's apparently nothing like this for forceRename() or forceMove(). Got to do it yourself I guess.