title: Dynamicaly populating a combobox with values from a Map based on what's selected in another combobox
body: <p>Ok, here's one for the Java/JavaScript gurus:</p>
  
  <p>In my app, one of the controllers passes a TreeMap to it's JSP. This map has car manufacturer's names as keys and Lists of Car objects as values. These Car objects are simple beans containing the car's name, id, year of production etc.
  So, the map looks something like this (this is just an example, to clarify things a bit):</p>
  
  <p>Key: Porsche<br/>
  Value: List containing three Car objects(for example 911,Carrera,Boxter with their respectable years of production and ids)<br/>
  Key: Fiat<br/>
  Value: List containing two Car objects(for example, Punto and Uno)<br/>
  etc...</p>
  
  <p>Now, in my JSP i have two comboboxes. One should receive a list of car manufacturers(keys from the map - this part I know how to do), and the other one should <strong>dynamicaly change</strong> to display the names of the cars when the user selects a certain manufacturer from the first combobox. So, for example, user selects a "Porsche" in the first combobox, and the second immediately displays "911, Carrera, Boxter"...</p>
  
  <p>After spending a couple of days trying to find out how to do this, I'm ready to admit defeat. I tried out a lot of different things but every time I hit a wall somewehere along the way. Can anybody suggest how I should approach this one?
  Yes, I'm a JavaScript newbie, if anybody was wondering...
  <br/></p>
  
  <p>EDIT: I've retagged this as a code-challenge. Kudos to anybody who solves this one without using any JavaScript framework (like JQuery).</p>