public static boolean mergeFiles(String[] fpaths, String resultPath) {

  if (fpaths == null || fpaths.length < 1 || TextUtils.isEmpty(resultPath)) {

    return false;

  }

  if (fpaths.length == 1) {

    return new File(fpaths[0]).renameTo(new File(resultPath));

  }

 

  File[] files = new File[fpaths.length];

  for (int i = 0; i < fpaths.length; i ++) {

    files[i] = new File(fpaths[i]);

    if (TextUtils.isEmpty(fpaths[i]) || !files[i].exists() || !files[i].isFile()) {

      return false;

    }

  }

 

  File resultFile = new File(resultPath);

 

  try {

    int bufSize = 1024;

    BufferedOutputStream outputStream = new BufferedOutputStream(new FileOutputStream(resultFile));

    byte[] buffer = new byte[bufSize];

 

    for (int i = 0; i < fpaths.length; i ++) {

      BufferedInputStream inputStream = new BufferedInputStream(new FileInputStream(files[i]));

      int readcount;

      while ((readcount = inputStream.read(buffer)) > 0) {

        outputStream.write(buffer, 0, readcount);

      }

      inputStream.close();

    }

    outputStream.close();

  } catch (FileNotFoundException e) {

    e.printStackTrace();

    return false;

  } catch (IOException e) {

    e.printStackTrace();

    return false;

  }

 

  for (int i = 0; i < fpaths.length; i ++) {

    files[i].delete();

  }

 

  return true;

}

public static void main(String[] args) {

     mergeFiles(new String[]{"D:/in_1.txt", "D:/in_2.txt", "D:/in_3.txt"}, "D:/output.txt");

}