java Memorymapfile demo

import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.CharBuffer;
import java.nio.channels.FileChannel;
import java.nio.channels.FileChannel.MapMode;

public class memorymapfiledemo {
    final static String filepath = "/home/hadoop/test/java.txt";

    public static void main(String[] args) throws IOException {
        writefile(filepath);
        readfile(filepath);
    }

    static void writefile(String _filepath) throws IOException {
        File _file = new File(_filepath);
        RandomAccessFile raf = new RandomAccessFile(_file, "rw");
        FileChannel fc = raf.getChannel();
        int buffersize = 1024 * 8;
        CharBuffer cb = fc.map(MapMode.READ_WRITE, 0, buffersize)
                .asCharBuffer();
        String lineseperator = java.security.AccessController
                .doPrivileged(new sun.security.action.GetPropertyAction(
                        "line.separator"));
        String content = "";
        long offset = 0;
        for (int i = 1; i <= 1000; i++) {
            content = "Line" + i + " hello java" + lineseperator;
            if ((cb.limit() - cb.position()) < content.length()) {
                offset += cb.position();
                cb = fc.map(MapMode.READ_WRITE, offset, buffersize)
                        .asCharBuffer();
            }
            cb.put(content);
        }
        fc.close();
        raf.close();
    }

    static void readfile(String _filepath) throws IOException {
        File _file = new File(_filepath);
        RandomAccessFile raf = new RandomAccessFile(_file, "rw");
        FileChannel fc = raf.getChannel();
        long totalsize = fc.size();
        int buffersize = 1024 * 8;
        long offset = 0;
        CharBuffer cb = fc.map(MapMode.READ_ONLY, 0, buffersize).asCharBuffer();
        while (offset < totalsize) {
            while (cb.hasRemaining()) {
                System.out.print(cb.get());
            }
            offset += cb.position();
            cb = fc.map(MapMode.READ_ONLY, offset, buffersize).asCharBuffer();
        }
        fc.close();
        raf.close();
    }
}