Java : Read last n lines of a HUGE file

Question

I want to read the last n lines of a very big file without reading the whole file into any buffer/memory area using Java.

I looked around the JDK APIs and Apache Com

Answer 1

Here is the best way I've found to do it. Simple and pretty fast and memory efficient.

public static void tail(File src, OutputStream out, int maxLines) throws FileNotFoundException, IOException {
    BufferedReader reader = new BufferedReader(new FileReader(src));
    String[] lines = new String[maxLines];
    int lastNdx = 0;
    for (String line=reader.readLine(); line != null; line=reader.readLine()) {
        if (lastNdx == lines.length) {
            lastNdx = 0;
        }
        lines[lastNdx++] = line;
    }

    OutputStreamWriter writer = new OutputStreamWriter(out);
    for (int ndx=lastNdx; ndx != lastNdx-1; ndx++) {
        if (ndx == lines.length) {
            ndx = 0;
        }
        writer.write(lines[ndx]);
        writer.write("\n");
    }

    writer.flush();
}