OLAP4J - open Java API for OLAP

olap4j is an open Java API for OLAP.

Think of it as like JDBC, except for accessing multi-dimensional data.

olap4j is designed to be a common API for any OLAP server, so you can write an application on one OLAP server and easily switch it to another. And built on that API, there will be a growing collection of tools and components.

You can find more info on website: http://www.olap4j.org/

Source: Chris Webb blog.