Why BufferedWriter is not writing into the file over the opened FileChannel?

Question

Below is my code. I am able to successfully read the file. But not able to re-write onto it with the replaced content using BufferedWriter. But can do it with ByteBuffer. Any suggestions please where I am going wrong.

myFile.txt content:

Key1-Value1
Key2-Value2
Key3-Value3

Java code below:

String fileAbsolutePath = "C:\\myPath\\myFile.txt";

        try {
            RandomAccessFile file = new RandomAccessFile(fileAbsolutePath, "rw");
            FileChannel fileChannel = file.getChannel();
            FileLock lock = fileChannel.lock();
            // read from the channel
            BufferedReader bufferedReader = new BufferedReader(Channels.newReader(fileChannel, "UTF-8"));
        List<String> filteredList = bufferedReader.lines().filter(line -> !line.contains("KEY1-VALUE1")).onClose(() -> {
            try {
                bufferedReader.close();
            } catch (IOException ex) {
                throw new UncheckedIOException(ex);
            }
        }).collect(Collectors.toList());
            fileChannel.truncate(0);
            BufferedWriter bufferedWriter = new BufferedWriter(Channels.newWriter(fileChannel, "UTF-8"));
            for (String string : list) {
                bufferedWriter.write(string);//does n't work
                bufferedWriter.newLine();
            }
            lock.release();
            file.close();
            fileChannel.close();
        } catch (Exception e) {
            e.printStackTrace();
        }

ByteBuffer part which works:

ByteBuffer buff = null;
            for (int i = 0; i < filteredList.size(); i++) {
                buff = ByteBuffer.wrap(filteredList.get(i).concat("\n").getBytes(StandardCharsets.UTF_8));
                fileChannel.write(buff);
            }

The challenge is achieving the same with the help of BufferedWriter

Updated code after trying try-with-resources

try (RandomAccessFile file = new RandomAccessFile(fileAbsolutePath, "rw");
                FileChannel fileChannel = file.getChannel();
                FileLock lock = fileChannel.lock();
                BufferedReader bufferedReader = new BufferedReader(Channels.newReader(fileChannel, "UTF-8"));
                BufferedWriter bufferedWriter = new BufferedWriter(Channels.newWriter(fileChannel, "UTF-8"))) {

            // read from the channel
            List<String> list = bufferedReader.lines().filter(line -> !line.contains("Key1-Value1"))
                    .collect(Collectors.toList());
            fileChannel.truncate(0);
            list.forEach(item -> {
                try {
                    bufferedWriter.write(item.concat("\n"));
                } catch (IOException e) {
                    e.printStackTrace();
                }
            });
            bufferedWriter.flush();
        }

Answer 1

You do not flush the BufferedWriter at the end, which means it contains some or all of the lines you wish to write back. Add a flush() before you close the channels to ensure the buffer is written out:

bufferedWriter.flush();
lock.release();

Ideally you should use try() with resources so that all your files are cleanly closed at appropriate time.