How do I know where I am in the file if I read it with a FileReader?

Question

I have a bit of code like this:

FileReader fr = new FileReader(file);
BufferedReader reader = new BufferedReader(fr);
for (int i=0;i<100;i++) 
{
   String line = reader.readLine(); 
   ...
}

// at this point I would like to know where I am in the file.
// let's assign that value to 'position' 
// then I would be able to continue reading the next 100 lies (this could be done later on ofcourse... )
// by simply doing this: 

FileReader fr = new FileReader(file);
fr.skip(position); 
BufferedReader reader = new BufferedReader(fr);
for (int i=0;i<100;i++) 
{
   String line = reader.readLine(); 
   ...
}

I can't figure out how to get/compute the value for 'position'.

Two things: I don't have obviously a fixed length file (i.e.: every line has a different length) I need to make it work on any system (linux, unix, windows) so I am not sure if I can assume the length of newline (whether it's one or two chars)

Any help very much appreciated.

Thanks,

Answer 1

If you can keep the file opened, you can try with mark() and reset(). If you have to close the file and reopen, try FileInputStream.getChannel().position() and FileInputStream.skip()

Answer 2

I think you should use FileChannel. Example:

import java.io.FileInputStream;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;

public class FileRead {
    public static void main(String[] args) {
    try {
        String path = "C:\\Temp\\source.txt";
        FileInputStream fis = new FileInputStream(path);
        FileChannel fileChannel = fis.getChannel();

        ByteBuffer buffer = ByteBuffer.allocate(64);

        int bytesRead = fileChannel.read(buffer);
        while (bytesRead != -1) {
            System.out.println("Read: " + bytesRead);
            System.out.println("Position: " + fileChannel.position());
            buffer.flip();

            while (buffer.hasRemaining()) {
                System.out.print((char) buffer.get());                    
            }

            buffer.clear();
            bytesRead = fileChannel.read(buffer);
        }

        fis.close();
    } catch (IOException e) {
        e.printStackTrace();
    }
}
}