Virtual Library Renovations

The Virtual Library example application has now been completely renovated for Tapestry 4.0. It now looks like an application built for Tapestry 4.0 from scratch. It makes heavy use of annotations, friendly URLs (including some custom friendly URLs), application HiveMind services ... all the 4.0 goodies. The only thing that didn't change was the underlying EJBs (except to switch over to HSQL from McKoi).

I'll be writing up some comparison documentation for the next beta.

One of the areas I'm really happy with is the inheritance hierarchy; I was able to flatten it quite a bit. The old code had several levels of inheritance, centered around the pageValidate() method used to restrict portions of the site to logged in users, or to users with admin privilege. The new system moves all that logic to a single base class and drives it by @Meta annotations (with some subclasses overriding the @Meta from the base class).

Part of the transformation was the removal of the VirtualLibraryEngine; all the logic that used to be there is now in various HiveMind services. I borrowed a page from Spring and created a RemoteTemplate service that can execute a RemoteCallback (with retry logic for RemoteExceptions). That removed lots of very ugly loop-and-retry logic from many pages and components, and replaced it with less-ugly RemoteCallback inner classes.

I hope people will take a close look at the new Virtual Library; it continues to be a small, manageable application that can serve as an excellent template for building much more ambitious, real-world projects.

Hopefully in the next beta release, these examples will be distributed as a pre-configured JBoss installation, rather than a patch on top of JBoss. This will be bigger but even easier to setup and execute. Probably in 4.1 we'll shift the code around to use JPox, Cayenne or Hibernate and get away from requiring EJBs or an application server.