JAVA the smartest embedded persistance solution

I'm developing GWT application, so I hav开发者_StackOverflow社区e JAVA server with next to nothing configuration. And I'm in need of persisting my DomainObjects.

It's a tree with root Class containing String id, List<ClassB>, ClassC, List<ClassD> CLassB,C,D contains only String and primitives.

I need to be able to search by String id of root class and retrieve whole tree. I need to be able to update as well.

Whta is teh simpliest/smartest solution? (I know how to do that with Spring,Hibernate and HSQLDB - but that seems like an overkill) I want it to be as much portable as possible so embedded solution is the one I seek.

We use ORMLite http://ormlite.com/ for our handheld data-entry devices. It is very lightweight and simple to set up and use, and follows the same annotation-based configuration model as hibernate.

One thing to note is that although Hibernate may be overkill, there are many things it makes nice and simple. ORMLite is more suited where you want a lightweight implementation or more control over the output database, whereas a tool like Hibernate makes development a bit easier.