generate a 16 character unique key in java

Question

I want to know what is the best approach in java to generate a 16 char unique key ? Is there any open source library which already provides such functionality. Also I need the uniqueness to be mentained even after server restart.

Could you suggest the best approach for above requirement.

Also could someone point me to, where can i get reference for writing a robust hashcode method where the hashcode would be genarated out of many alphanumeric fields?

Answer 1

You could use the UUID class in the JRE. It generates a 128-bit key.

As for hash codes, this is also available in the JRE:

MessageDigest md = MessageDigest.getInstance("MD5");
byte[] hashCode = md.digest(...);

Answer 2

Random r = new SecureRandom();
byte[] b = new byte[16];
r.nextBytes(b);
String s = org.apache.commons.codec.binary.Base64.encodeBase64String(b);
return s.substring(0, 16); 

Good and robust way