ss =  new  ServerSocket( 44444 );
Socket s = ss.accept();
BufferedInputStream bis =  new  BufferedInputStream(s.getInputStream());
BufferedOutputStream bos =  new  BufferedOutputStream( new  FileOutputStream("file"));
Пишешь примерно так:
 byte [] buffer =  new   byte [ 4096 ];
 int  read = bis.read(buffer);
 while  (read !=  0 ){
    bos.write(buffer,  0 , read);
    read = bis.read(buffer);
}

bos.flush();
bos.close();
bis.close();
s.close();

Socket s =  new  Socket("Your host",  44444 );
BufferedInputStream bis =  new  BufferedInputStream( new  FileInputStream("file"));
BufferedOutputStream bos =  new  BufferedOutputStream(s.getOutputStream());
Пишешь примерно так:
 byte [] buffer =  new   byte [ 4096 ];
 int  read = bis.read(buffer);
 while  (read !=  0 ){
    bos.write(buffer,  0 , read);
    read = bis.read(buffer);
}

bos.flush();
bos.close();
bis.close();
s.close();