Do you know what the browser is sending you when the user submits the form? Do you know how to retrieve parameters from the request? Are you retrieving them from your servlet or are you passing the map of parameters to your form bean? Is there a fixed number of checkboxes? Do you know their names ahead of time? Do your checkboxes have values or are you only checking for null or not null. Do your checkboxes have different names or do they all share a name?
The more information you can give us, the more we can help you.