Struts doesn't define anything for the data access layer.
It helps you write MVC applications, and provides a translator between your view (jsp pages) and your model (action forms/actions), but once you get to that point its all standard java code.
You have a few alternatives
1 - write java classes to handle the data access layer: Data Access Objects (or DAOs) using standard java/jdbc.
2 - Use a tool like hibernate to do your data layer handling.
Struts itself though won't help at all with this.