File file1 = new File("D:\\dvd.avi");
    InputStream dvdinput = new FileInputStream(file1);
    InputStream in = new BufferedInputStream( dvdinput );
    
    File file2 = new File("D:\\dvd1.avi");
    OutputStream outputStream = new FileOutputStream( file2 );
    OutputStream outputbuffer = new BufferedOutputStream( outputStream, 512 );
    
    System.out.println(in.available());

    if( !file2.exists() ){
        file2.createNewFile();
    }
    byte b[] = new byte[ in.available() ];
    int len= -1;
    while( (len=in.read(b)) != -1 ){ // 这里你弄错了！
        outputbuffer.write(b,0,len); // 这里读完了，马上写入到新文件
    }
    outputbuffer.flush();
    outputbuffer.close();
    in.close();