Hexadecimal to Integer in Java

I am trying to convert a String hexadecimal to an integer. The string hexadecimal was calculated from a hash function (sha-1). I get this error : java.lang.NumberFormatException. I guess it doesn't like the String representation of the hexadecimal. How can I achieve that. Here is my code :

public Integer calculateHash(String uuid) {

    try {
        MessageDigest digest = MessageDigest.getInstance("SHA1");
        digest.update(uuid.getBytes());
        byte[] output = digest.digest();

        String hex = hexToString(output);
        Integer i = Integer.parseInt(hex,16);
        return i;           

    } catch (NoSuchAlgorithmException e) {
        System.out.println("SHA1 not implemented in this system");
    }

    return null;
}   

private String hexToString(byte[] output) {
    char hexDigit[] = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
            'A', 'B', 'C', 'D', 'E', 'F' };
    StringBuffer buf = new StringBuffer();
    for (int j = 0; j < output.length; j++) {
        buf.append(hexDigit[(output[j] >> 4) & 0x0f]);
        buf.append(hexDigit[output[j] & 0x0f]);
    }
    return buf.toString();

}

For example, when I pass this string : _DTOWsHJbEeC6VuzWPawcLA, his hash his : 0xC934E5D372B2AB6D0A50B9F0341A00ED029BDC15

But i get : java.lang.NumberFormatException: For input string: "0xC934E5D372B2AB6D0A50B9F0341A00ED029BDC15"

I really need to do this. I have a collection of elements identified by their UUID which are string. I will have to store those elements but my restrictions is to use an integer as their id. It is why I calculate the hash of the parameter given and then I convert to an int. Maybe I am doing this wrong but can someone gives me an advice to achieve that correctly!!

Thanks for your help !!