is it a must to use kodo jdo if want to integrate with spring? from my understanding kodo is not free. any free implementation of jdo with spring? any such demo come with source code?
Spring JDO support should be able to work with any implementation that is compliant to the JDO spec.
For example, here is a tutorial for using the open source JPox JDO implementation with Spring.
Datanucleus. They are the maintainer of JPOX, the reference implementation of JDO. The HUGE advantage of using Datanucleus for your application development is that the Google App-Engine uses it. That means it can be easily deployed to the Google Cloud and you don't have to worry a bit about what happens to persist the data, or that it will scale in a high reliability, high availability manner.