java - Delete last line in text file

Question

I am tying to erase the last line in a text file using Java; however, the code below deletes everything.

public void eraseLast()
{
    while(reader.hasNextLine()) {
        reader.nextLine();

        if (!reader.hasNextLine()) {
            try {
                fWriter = new FileWriter("config/lastWindow.txt");

                writer = new BufferedWriter(fWriter);
                writer.write("");
                writer.close();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    }
}

Answer 1

If you wanted to delete the last line from the file without creating a new file, you could do something like this:

RandomAccessFile f = new RandomAccessFile(fileName, "rw");
long length = f.length() - 1;
do {                     
  length -= 1;
  f.seek(length);
  byte b = f.readByte();
} while(b != 10);
f.setLength(length+1);
f.close();

Start off at the second last byte, looking for a linefeed character, and keep seeking backwards until you find one. Then truncate the file after that linefeed.

You start at the second last byte rather than the last in case the last character is a linefeed (i.e. the end of the last line).