code: private void cleanTargetDirectory(PrintStream logger, String targetDirectory) throws IOException {
          File target = new File(targetDirectory);
          if (target.exists()) {
              File[] subfolders = target.listFiles((FilenameFilter) DirectoryFileFilter.INSTANCE);
              if (subfolders.length > 0) {
                  logger.println("  Cleaning target directory...");
              }
              for (File subfolder : subfolders) {
                  if (subfolder.listFiles((FilenameFilter) new SuffixFileFilter(".vproj")).length > 0) {
                      logger.println("    Deleting subfolder of target directory: " + subfolder.getAbsolutePath());
                      FileUtils.deleteDirectory(subfolder);
                  } else {
                      logger.println("    Skipping delete of directory '" + subfolder.getAbsolutePath() + "' because it does not contain any *.vproj file.");
                  }
              }
          }
      }
docs: Cleans all sub-folders containing *.vproj file.