Implement an application to solve a specific real world problem. It can be anything, may be you have already such a project.
Some technology constraints:
Use a database (e.g. MySQL)
Data access to the databases should be realized using an ORM framework (Hibernate)
A user interface should be created for easy interaction with the application (use JSF or JSP, Spring)
The application will expose a set of REST WebServices, which will be consumed by the UI.
Use Maven to build project.
27 freelancers are bidding on average €150 for this job
I've been working with development for a long time using the techs you described. Actually I made a lot of projects like what you want, so I would take about 3 days to implement it.