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();
         }