从一个URL下载原始数据，基于byte字节，得到byte数组

 public static byte[] loadRawDataFromURL(String u) throws Exception {
         URL url = new URL(u);
         HttpURLConnection conn = (HttpURLConnection) url.openConnection();

         InputStream is = conn.getInputStream();
         BufferedInputStream bis = new BufferedInputStream(is);

         ByteArrayOutputStream baos = new ByteArrayOutputStream();
 　　　　　//缓存2KB
         final int BUFFER_SIZE = 2*1024;
         final int EOF = -1;

         int c;
         byte[] buf = new byte[BUFFER_SIZE];

         while (true) {
             c = bis.read(buf);
             if (c == EOF)
                 break;

             baos.write(buf, 0, c);
         }

         conn.disconnect();
         is.close();

         byte[] data = baos.toByteArray();
         baos.flush();

         return data;
     }