public static void combineFiles(String dir, String outputTxt)
			throws IOException {
		File directory = new File(dir);
		File file = new File(outputTxt);
		if (!file.exists()) {
			file.createNewFile();
		}
		File[] files = directory.listFiles();
		BufferedWriter bw = new BufferedWriter(new FileWriter(file));
		for (File f : files) {
			if (f.isFile() && isTxtFile(f.getName())) {
				getLogger().info("file name : " + f.getAbsolutePath());
				List<String> sentences = CoreNLPHelper.getHelper().sentencesFromText(f.getAbsolutePath());
				for (String sentence : sentences) {
					bw.write(sentence.toLowerCase());
					bw.write("\n");
				}
			} else if (f.isDirectory()) {
				recur(f, bw);
			}
		}
		bw.close();
	}