Populate list box from selection in drop down menu

How do I populate a list box from selection in drop down menu?
The options in my list box i need are from a field in my sql database and
change according to what is selected in the drop down menu.
The options in the drop down menu are from my database as well.
The page is a .jsp. I can't seem to integrate the java with the javascript.
All i've been able to find on the internet is populated from a static array made
in javascript or its using php or asp. How do I pull an array from my
database and use that in the javascript?
Completely new to javascript. Have no idea where to start. I have no code.