Try some of these
http://www.java-source.net/open-source/content-managment-systems

The choice would depend on what exactly is the requirement. I have
found AtLeap CMS to be a good one. Before sticking to AtLeap I had
tried several other open source and free CMS like InfoGlue and
OpenCMS, I found both of them pretty confusing.

https://atleap.dev.java.net [AtLeap]
The UI is Tile based, I found it easy to configure. Though in my
opinion it would have been better if it was based on Sitemesh.

The Struts is WAF and in Business layer AtLeap uses Spring and
Hibernat.

It has a fairly good Administration module with flexibility to create
user and grant access to a particular resource. Once the basic CMS is
running all the resource is persisted in the Database, hence offers
ease in backing up the data.

--
Ck
http://www.gfour.net

OpenEdit seems to be a nice little CMS. It lacks some features for a
real large sites, but otherwise it looks quite good.

As you have not stated any requirements for your CMS it's more less
impossible to give you any advice.

Thomas

As far as I know PHPNuke is not a CMS but a full portal.

For something similar in Java you should look at
Liferay (www.liferay.com) or JBoss Portal
(www.jboss.com).

If you really want a CMS look at OpenCMS (www.opencms.org).

Arne