How to control selecting a single item in a rich:pickList

[josdaniel]

We have a requirement to select only one element from rich:pickList. How do you disable the controls or prevent folks from moving additional data from the left hand side after an item is selected.

[ilya_shaikovsky]

I think you could

1) attach the validator which will check that condition

2) put a4j:ajaxValidator to onlistchanged which will validate the condition and put the message if the user selected more than two items.