Dave wrote: > When a backing bean is dependent on some data that are initialized > by previous page, it works fine normally. But if user click Back/Refresh > on browser, then the data is not available anymore to the backing bean. > This will result in NullPointerException because the data is null. How > to catch this issue and display a nice informative message, definitely > not Exception? Thanks for ideas. Dave > Sorry, my first answer was too short, to clarify things a little bit, the problem you encounter is due to the request scope, a bean declared in request scope lives only one request, now if you do a refresh you might lose important data along the way, the same goes for back.
There are various solutions to the problem, the shale token stuff, I yet have to check out, but one solution is to use constructs which enable scopes bigger than request. One solution definitely would be to dump the backend bean into the session that way non traversed values would survive a refresh. Another one would be to use a lot of hidden fields, for the non visible data which has to survive which is a maintenance nightmare. Generally the currently possibly best approach would be to use x:saveState which stores beans for every page where a x:saveState tag is hit with the same declaration, or to use some kinde of dialog-scoping system: Following systems currently are available: Shale Dialog Seam Seam at least is rather heavy on the configuration side, but it looks like the most interesting approach in this area. Shale Dialog I have not looked into yet, the possible most lightweight approach however probably is x:saveState...
