public static InputStream skipFully(InputStream in,long howMany)throws Exception{
        long remainning = howMany;
        long len = 0;
        while(remainning>0){
            len = in.skip(len);
            remainning -= len;
        }
        return in;
    }

------解决方案--------------------

Java code
Thread dl = new Thread(){
                    public void run(){
                        try{
                            String n = jtf.getText();
                            int s = n.lastIndexOf("/");
                            String tar = n.substring((s+1));

                            URL url = new URL(jtf.getText());
                            URLConnection uc = url.openConnection();
                            long total = uc.getContentLength();

                            InputStream is = uc.getInputStream();
                            BufferedInputStream bis = new BufferedInputStream(is,1024*1024*10);
                            FileOutputStream fos = new FileOutputStream(tar,true);
                            BufferedOutputStream bos = new BufferedOutputStream(fos,1024*1024*10);

                            File tarFile = new File(tar);
                            long count = tarFile.length();
                            is.skip(count);

                            byte[] data = new byte[1024*1024*10];
                            int (Stri