Java实现断点下载Demo

//1、声明URL
        String path="http://localhost:8080/day22_DownLoad/file/a.rmvb";
        URL url=new URL(path);
        //2、设置已下载文件
        String savePath="d:\a.rmvb";
        File file=new File(savePath);
        long size=file.length();//文件当前大小，刚开始时返回0
        System.out.println(size);
        //3、设置连接
        HttpURLConnection conn=  (HttpURLConnection) url.openConnection();
        //4、设置访问类型
        conn.setRequestMethod("GET");
        //5、设置下载区间
        conn.setRequestProperty("range","bytes="+size+"-");
        conn.connect();
        //6、状态码
        int code=conn.getResponseCode();//断点是206
        if(code==206)
        {
            InputStream in=conn.getInputStream();
            int serviceSize=conn.getContentLength();
            //必须使用
            RandomAccessFile out=new RandomAccessFile(file, "rw");
            //从size字节开始写
            out.seek(size);
            byte[] b=new byte[1024];
            int len=-1;
            while((len=in.read(b))!=-1)
            {
                out.write(b,0,len);
            }
            out.close();
        }