Sequential Guid in Java

See this article: http://www.informit.com/articles/article.aspx?p=25862&seqNum=7 (linked to Page 7).

It contains an algorithm for what the author refers to as "COMB" Guids; I reproduce his code (SQL) below:

SET @aGuid = CAST(CAST(NEWID() AS BINARY(10)) 
+ CAST(GETDATE() AS BINARY(6)) AS UNIQUEIDENTIFIER)

Trivial to convert this to Java, or your desired language. The obvious underlying principle is to make the date a component of the Guid. The entire article is a good read, as he does a nice analysis of the performance of the various approaches.

For sequential UUIDs, you are looking for a version 1 UUID. Java UUID Generator project seems to work quite well and is pretty easy to use:

Generators.timeBasedGenerator().generate().toString()

This page links to a couple of version 1 (sequential) UUID implementations in Java: http://johannburkard.de/blog/programming/java/Java-UUID-generators-compared.html