How to use Java nio. channels. Filechannel reads ByteBuffer and implements similar behavior similar to BufferedReader #readline()

I want to use Java nio. channels. Filechannel to read the file, but I want to read each line, just like BufferedReader #readline() The reason why I need to use Java nio. channels. Filechannel instead of Java IO is because I need to lock the file and read it line by line from the locked file So I forced the use of Java nio. channels. FileChannel. Please help

Edit this is my code trying to use FileInputStream to get filechannel

public static void main(String[] args){
    File file = new File("C:\\dev\\harry\\data.txt");
    FileInputStream inputStream = null;
    BufferedReader bufferedReader = null;
    FileChannel channel = null;
    FileLock lock = null;
    try{
        inputStream = new FileInputStream(file);
        channel  = inputStream.getChannel();
        lock = channel.lock();
        bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
        String data;
        while((data = bufferedReader.readLine()) != null){
            System.out.println(data);
        }
    }catch(IOException e){
        e.printStackTrace();
    }finally{
        try {
            lock.release();
            channel.close();
            if(bufferedReader != null) bufferedReader.close();
            if(inputStream != null) inputStream.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

When the code is here, lock = channel lock();, It immediately goes to finally and lock is still null, so lock Release() generates NullPointerException I don't know why?

Solution

The reason is that you need to use fileoutpustream instead of FileInputStream

FileOutputStream outStream = null;
        BufferedWriter bufWriter = null;
        FileChannel channel = null;
        FileLock lock = null;
        try{
            outStream = new FileOutputStream(file);
            channel  = outStream.getChannel();
            lock = channel.lock();
            bufWriter = new BufferedWriter(new OutputStreamWriter(outStream));
        }catch(IOException e){
            e.printStackTrace();
        }

This code is very good for me

NullPointerException actually hides the real exception, notwritablechannelexception For locking, I think we need to use OutputStream instead of InputStream