java nio buffer读取数据乱码问题

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(1024);

int count = fileChannel.read(buffer);
while (count != -1) {
buffer.flip();
CharBuffer charBuffer = CharBuffer.allocate(1024);
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(1024);
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();
}
}