static int deleteAllFilesInDirectory_minPathLength = 10;

static void deleteAllFilesInDirectory(File dir) {
  deleteAllFilesInDirectory(dir, false, false);
}

static void deleteAllFilesInDirectory(File dir, boolean verbose, boolean testRun) {
  dir = getCanonicalFile(dir);
  assertTrue(f2s(dir), l(f2s(dir)) >= deleteAllFilesInDirectory_minPathLength);
  File[] files = dir.listFiles();
  if (files == null) return;
  for (File f : files) {
    if (!isSymLink(f) && f.isDirectory()) // just delete the symlink, don't follow it
      deleteDirectory(f, verbose, testRun);
    else {
      if (verbose)
        print((testRun ? "Would delete " : "Deleting ") + f.getAbsolutePath());
      if (!testRun)
        f.delete();
    }
  }
}

Began life as a copy of #1001058