Extract hexadecimal values from a percent encoded URL

Question

Let's say for example i have URL containing the following percent encoded character : %80
It is obviously not an ascii character.
How would it be possible to convert this value to the corresponding hex string in Java. i tried the following with no luck.Result should be 80.

    public static void main(String[] args) {
        System.out.print(byteArrayToHexString(URLDecoder.decode("%80","UTF-8").getBytes()));
    }
    public static String byteArrayToHexString(byte[] bytes)
    {
      StringBuffer buffer = new StringBuffer();
      for(int i=0; i<bytes.length; i++)
      {
        if(((int)bytes[i] & 0xff) < 0x10)
        buffer.append("0");
        buffer.append(Long.toString((int) bytes[i] & 0xff, 16));
      }
      return buffer.toString();
  }

Answer 1

The best way to deal with this is to parse the url using either java.net.URL or java.net.URI, and then use the relevant getters to extract the components that you require. These will take care of decoding any %-encoded portions in the appropriate fashion.

The problem with your current idea is that %80 does not represent "80", or 80. Rather it represents a byte that further needs to be interpreted in the context of the character encoding of the URL. And if the encoding is UTF-8, then the %80 needs to be followed by one or two more %-encoded bytes ... otherwise this is a malformed UTF-8 character representation.

Answer 2

I don't really see what you are trying. However, I'll give it a try.

• When you have got this String: "%80" and you want to got the string "80", you can use this:

  String str = "%80";
  String hex = str.substring(1); // Cut off the '%'
  

• If you are trying to extract the value 0x80 (which is 128 in decimal) out of it:

  String str = "%80";
  String hex = str.substring(1); // Cut off the '%'
  int value = Integer.parseInt(hex, 16);
  

• If you are trying to convert an int to its hexadecimal representation use this:

  String hexRepresenation = Integer.toString(value, 16);