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0ne of the benefits to developing using Tapestry is its robust exception handling support. We'll demonstrate these by creating invalid URLs.
As we just demonstrated, Tapestry is quite careful about conversational state. What happens if all the conversation state is lost?
Start up adder application then enter a few numbers. Go back to the window executing Jetty and stop it, then restart it.
Now, try to add an additional number to the list.
Because Tapestry can't find any information about your session, it assumes the session timed out and was discarded, and so presents the default error page for this situation.
Remember that most Tapestry URLs are very conversational, they only make sense as the most recent request in a series of requests exchanged between the client and the server.
This means that many pages in a Tapestry application can't be bookmarked; the URL that would be stored in the client's web browser is not meaningful. Creating bookmarkable pages is a subject of a later tutorial.