如何使用FileInputStream和BufferReader实现RandomAccessFile的seek（）和getFilePointer（）？

Question

I would like to Open a file containing UTF-8 encoded text, Can able to set position, Read 25 lines, Can able to get position.

Unfortunately RandomAccessFile does not support UTF-8 encoding. So I have written this code. I recursive call getParsedLines() method with the returned offset value to read next 25 lines but it prints first 1-25 rows, then print 349-373, 695-719 and so on.

public long getParsedLines(File file, long offset) {


    int counter = 0;
    FileInputStream fis = null;
    InputStreamReader streamReader = null;
    BufferedReader br = null;
    try {
        fis = new FileInputStream(file);
        fis.getChannel().position(offset);
        streamReader = new InputStreamReader(fis, "UTF8");
        br = new BufferedReader(streamReader);
        String str;
        while (counter <= 24) {
            if ((str = br.readLine()) != null) {
                System.out.println(str);
            } else {
                offset = -1;
                break;
            }
            counter++;
        }
        if (fis != null) {
            offset = fis.getChannel().position();

        }
    } catch (IOException ex) {
    } finally {
        try {
            if (fis != null) {
                fis.close();
            }
        } catch (IOException ex) {
        }

    }

    return offset;
}

how can I get last offset correct so I can print 1-25, 26-50, 51-75. 76-100 and so on.

Yes.. For some backward compatibility I have some constraint that I have to read text file "line by line" using readLine() and read only 25-25 lines at a time not the whole text.

Answer 1

The BufferedReader reads ahead,so the position on the underlying file > the logical position the BufferedReader has reached. You could try DataInputStream.readLine(), which doesn't, and which is deprecated, and which doesn't handle the issues mentioned in the Javadoc against the deprecation.

Answer 2

It does support utf. please refer this url: http://www.tutorialspoint.com/java/io/randomaccessfile_seek.htm

Answer 3

If you must do it this way, you can use the BufferedReader.skip method to skip characters (having kept a count of the number of chars already read). But if possible, I'd suggest to just keep the same BufferedReader around (without closing it), so that it's automatically in the right place in any case.