A transition context stores and validates input data before the processor commits valid data to the process context. To do this, a transition context retains the input data of a form along with their related data elements and any ErrorInfo objects obtained when validating the data. This provides the following benefits:
▪ Security. A transition context acts as a specification of the input from a form. The system ignores any submitted information that is not in the transition context definition. This protects the application by preventing unexpected data from being inserted into the application context.
▪ Data filtering. A transition context defines the set of data related to a specific action in a page. This provides you with the ability to filter data items held within a page.
▪ Data integrity. A transition context preserves application data integrity because the processor only copies validated data into the application context.
▪ Transient error information. The life cycle of a transition context is very short and the toolkit takes advantage of this in its management of error information. The processor attaches an ErrorInfo object to any data elements in the transition context that are in error so that JSP code can use this object. Once the processor discards the transition context, it also discards these ErrorInfo objects.
By preserving input data in a transition context, the processor is able to restore input data should a user return to a canceled page.