public static void deleteFiles(File dir, FilenameFilter filter) {
        // validations
        if(dir == null) {
            throw new DataUtilException("The delete directory parameter can not be a null value");
        } else if(!dir.exists() || !dir.isDirectory()) {
            throw new DataUtilException("The delete directory does not exist: " + dir.getAbsolutePath());
        }

        // delete files
        File [] files;
        if(filter == null) {
            files = dir.listFiles();
        } else {
            files = dir.listFiles(filter);
        }
        if (files != null) {
            for(File file : files) {
                if(file.isFile()) {
                    if(!file.delete()) {
                        throw new DataUtilException("Failed to delete file: " + file.getAbsolutePath());
                    }
                }
            }
        }
    }