public static void main(String[] args) throws IOException {

        String charsetName = "GBK";

        String fileName = "data.txt";

        bufferToTxt(charsetName, fileName);

        txtToBuffer(charsetName, fileName);

    }

    public static void txtToBuffer(String charsetName, String fileName) {

        try {

            RandomAccessFile file = new RandomAccessFile(fileName, "rw");

            FileChannel fileChannel = file.getChannel();

            ByteBuffer buffer = ByteBuffer.allocate();

            int count = fileChannel.read(buffer);

            while (count != -) {

                buffer.flip();

                CharBuffer charBuffer = CharBuffer.allocate();

                Charset charset = Charset.forName(charsetName);

                CharsetDecoder decoder = charset.newDecoder();

                decoder.decode(buffer, charBuffer, true);

                charBuffer.flip();

                while (charBuffer.hasRemaining()){

                    System.out.print(charBuffer.get());

                }

                buffer.clear();

                count = fileChannel.read(buffer);

            }

            fileChannel.close();

            file.close();

        } catch (Exception e) {

            e.printStackTrace();

        }

    }

    public static void bufferToTxt(String charsetName, String fileName){

        try {

            RandomAccessFile file = new RandomAccessFile(fileName, "rw");

            FileChannel fileChannel = file.getChannel();

            ByteBuffer buffer = ByteBuffer.allocate();

            buffer.put("世界如此美妙！ good luck".getBytes(charsetName));

            buffer.flip();

            fileChannel.write(buffer);

            fileChannel.close();

            file.close();

        } catch (FileNotFoundException e) {

            e.printStackTrace();

        } catch (UnsupportedEncodingException e) {

            e.printStackTrace();

        } catch (IOException e) {

            e.printStackTrace();

        }

    }