I was looking for Java based OLAP servers or APIs and found OLAP4ALL, Oracle9i Java OLAP API and Mondrian Java OLAP Server. I liked Mondrian's tag library support through JPivot OLAP client project for interacting with Mondrian OLAP server which is a lot better than applet based approch of OLAP4ALL. Besides only Mondrian is open source. Any comment on Mondrian and OLAP4ALL please?
JOLAP was not correctly implemented by any vendors and has been quietly forgotten. Even though Oracle now owns both the Oracle OLAP Option (which has a proprietary Java OLAP API) and Essbase (which also has a proprietary Java OLAP API), we do not expect JOLAP to be resurrected.
I would also like to recommend a book on OLAP.The book is available on Amazon & you can buy an e-book directly from the publisher by writing OLAPWorldPress@gmail.com.
www.icCube.com is a new JAVA based OLAP server. As for a JAVA API, I do not know any widely accepted ones - during the development of icCube we've developped a thin JAVA layer to access XML/A server in an easier way. The source code is available both for the server and the API.