base64的解码

来源：互联网发布：数据点阵笔考试编辑：程序博客网时间：2024/06/05 09:35

开发百度地图的时候涉及到google地图坐标装换成百度地图坐标，百度有个api做这个转换，但是返回的数据是Base64编码的，所以需要对其进行解码。

  /*
   * base64的解码
   */
   public static String decodeBase64(String s)
   {

   ByteArrayOutputStream bos = new ByteArrayOutputStream();
   try
   {
   decodeBase64(s, bos);
   }
   catch (IOException e)
   {
   throw new RuntimeException();
   }
   String result = bos.toString();
   try
   {
   bos.close();
   bos = null;
   } catch (IOException ex) {
   System.err.println("Error while decoding BASE64: " + ex.toString());
   }
   return result;
   }

   private static void decodeBase64(String s, OutputStream os) throws IOException
   {
   int i = 0;

   int len = s.length();

   while (true)
   {
   while (i < len && s.charAt(i) <= ' ')
   i++;

   if (i == len)
   break;

   int tri = (decodeBase64(s.charAt(i)) << 18)
   + (decodeBase64(s.charAt(i + 1)) << 12)
   + (decodeBase64(s.charAt(i + 2)) << 6)
   + (decodeBase64(s.charAt(i + 3)));

   os.write((tri >> 16) & 255);
   if (s.charAt(i + 2) == '=')
   break;
   os.write((tri >> 8) & 255);
   if (s.charAt(i + 3) == '=')
   break;
   os.write(tri & 255);

   i += 4;
   }
   }
   private static int decodeBase64(char c)
   {
   if (c >= 'A' && c <= 'Z')
   return ((int) c) - 65;
   else if (c >= 'a' && c <= 'z')
   return ((int) c) - 97 + 26;
   else if (c >= '0' && c <= '9')
   return ((int) c) - 48 + 26 + 26;
   else
   switch (c)
   {
   case '+':
   return 62;
   case '/':
   return 63;
   case '=':
   return 0;
   default:
   throw new RuntimeException("unexpected code: " + c);
   }
   }