Re: [jsr-314-open] Evaluating EL in resource files

Ken Paulsen wrote: > > Question: How does EL parsing in a resource effect the caching > headers sent by the resource handler? > I was wondering the same thing. Ideally every resource that we serve up should specify http headers to encourage browser caching. Allowing EL expressions in resource content of course complicates this. If we want to allow arbitrary expressions then either: 1. We cannot allow these resources to be cached (bad). Or... 2. We need some way to ensure that every resource URL is always mapped to the same content (ie. EL expressions will always evaluate to the same result for any given URL). For #2, this might mean allowing a resource to tweak the URL in order to add information that ensures that the URL reflects the any EL dependencies. In the examples that Ed gave, it seems possible that the EL expressions such as this: #{resource['this:layout.css']} Would in fact always evaluate to the same value for any particular resource URL. If this were the case, then we could safely set cache headers for such resources. However, if arbitrary EL is allowed (eg. EL that references request/session scope data), then we must either do #1 or #2 above. Should we consider placing some limits on what types of EL expressions are allowed/resolved? For starters, possibly only provide access to #{resource} expressions? If these are guaranteed to evaluate the same for each requested URL, we should be able to cache these resources.

Imposing such a limitation might also help us to reduce the chance of collisions with Prototype's use of #{}. BTW, Weblets provides similar functionality: https://weblets.dev.java.net/doc_11/longdoc/usageresources.html The solution appears to be limited to resolving Weblet resource URLs (does not support arbitrary expressions). This functionality is similar in scope to my suggestion above. Andy