DLite offer a set of nifty C++ classes to store data in indexed files. It is fast, scalable reliable and easy to use (No libraries!!). I have gotten up to 10,000 io/sec using DLite.
JStore is a front end to DLite to store straight Java objects. Convenient for startup/personal projects and blazing fast !!! Where you don't exactly want to install or configure huge database systems (Just to use JDBC ? ) to test your ideas, put JStore in use.
Package contains two exhaustive examples, one in C++ and one in Java, besides ample test code.
Have fun.