Related projects that may prove useful to Prevayled applications

Queries

The JXPath Component

http://commons.apache.org/jxpath
http://commons.apache.org/jxpath/users-guide.html

Related articles

Java Object Querying Using JXPath - by Brian Agnew (08/03/2006)
http://today.java.net/pub/a/today/2006/08/03/java-object-querying-using-jxpath.html
Java object queries using JXPath - Query complex Java object trees using the XPath expression language - by Bart van Riel (21/03/2007)
http://www.javaworld.com/javaworld/jw-03-2007/jw-03-jxpath.html
JXPath Tutorial - by Bart van Riel
http://www.tfo-eservices.eu/wb_tutorials/pages/jxpath-tutorial.php

Groovy

An agile and dynamic language for the Java Virtual Machine
http://groovy.codehaus.org/Mixed+Java+and+Groovy+Applications
Mixed Java and Groovy Applications
http://groovy.codehaus.org/Mixed+Java+and+Groovy+Applications
Collections guide
http://groovy.codehaus.org/Collections
Maps guide
http://groovy.codehaus.org/JN1035-Maps (search for Grouping!)
Interception guide
http://groovy.codehaus.org/JN3515-Interception (intercepting BO methods?)

Collections

GNU Trove

High performance collections for Java
http://trove4j.sourceforge.net

Apache Commons Collections

Commons-Collections seek to build upon the JDK collections classes by providing new interfaces, implementations and utilities.
http://commons.apache.org/collections

The Google Collections Library

A suite of new collections and collection-related goodness for Java 5.0, brought to you by Google. (Still Alpha)
http://code.google.com/p/google-collections