Simpler: knowing that a seek on a RAF will move the FD with it,
you can reposition buffered streams on it. Here:
(I was too lazy to implement the DataInput and DataOutput, but you get
the point)

-----------

import java.io.*;

public class SuperRAF {
   
    public final RandomAccessFile raf;
    public final MyBIS bis;
    public final BufferedOutputStream bos;
    public final DataInputStream dis;
    public final DataOutputStream dos;
   
    public SuperRAF(RandomAccessFile raf, int bufsize) throws
IOException {
        this.raf = raf;
        bis = new MyBIS(new FileInputStream(raf.getFD()), bufsize);
        bos = new BufferedOutputStream(new FileOutputStream(raf.getFD
()), bufsize);
        dis = new DataInputStream(bis);
        dos = new DataOutputStream(bos);
    }
   
   
    public void flush() throws IOException {
        bos.flush();
    }
   
    public void seek(long pos) throws IOException {
        bos.flush();
        bis.clear();
        raf.seek(pos);
    }
   
    //=======
   
    static class MyBIS extends BufferedInputStream {
        MyBIS(InputStream is, int size) {
            super(is, size);
        }
       
        MyBIS(InputStream is) {
            super(is);
        }
       
        void clear() {
            super.count = 0;
            super.markpos = -1;
            super.pos = 0;
            super.marklimit = 0;
            //super.buf = don't waste that
        }
    }
   
}