Processes a form submit. If the form is finished, i.e. the form should not be redisplayed to the user, then this method returns true, otherwise it returns false. To know if the form was sucessfully validated, use the {@link #isValid()} method.
Form processing consists in multiple steps:
- all widgets read their value from the request (i.e. {@link #readFromRequest(FormContext)} is called recursively onthe whole widget tree)
- if there is an action event, call the FormHandler
- perform validation.
This processing can be interrupted by the widgets (or their event listeners) by calling {@link #endProcessing(boolean)}.