Re: partial evaluation / removing directives

On Thu, Jul 12, 2012 at 2:27 PM, Pete <[email protected]> wrote:
> Hi all,
> I'm working with some velocity files where I want to partially evaluate
> them, such that the only things actually evaluated are #parse (includes of
> other velocity templates in the same directory) and  $references to a
> resourceBundle variable passed in the context map.  In essence, all this is
> doing is combining a number of velocity files into one master velocity
> file, and localizing any resource bundle references to a given locale. All
> the main velocity directives in the velocity file(s) should be left
> unevaluated-   #set, #ifelse, #foreach etc. This way, the result could be
> redistributed and modified specific to a particular locale, with just one
> file instead of n based on the #parse structure.

interesting challenge!  glad i don't have to do it though. :)

> Up till now, I've been doing this in a somewhat roundabout way:
> 1. setting strict escape property to true
> 2. pre-processing the velocity templates by regexp replacing all instances
> of #if / #else/ #elseif/ #end / #foreach / #define / #break / #stop  #set /
> #evaluate with  \\#{$1}
> This adds a an escape character before each of these directives, and I can
> then call mergeTemplate on the result.  It works OK, sometimes, but I still
> run into some parsing issues now and again (eg not a robust solution). It
> also seems kind of heavy handed to have to preprocess these files using a
> regular expression and saving them before velocity gets a handle on them.
> It would even be a bit better if I could do this by reading them in and
> doing the rgexp in-memory rather than on the saved files, then using
> evaluate instead of mergeTemplate. But I assume that would cause problems
> for the #parse directives.

Why would evaluate cause problems for #parse??  If the engine is
configured the same, the #parse should work the same whether you enter
via file or string.

> I know velocity added a removeDirective() method in 1.6.2 which seems like
> it should be perfect for me - I could simply rip out all the directives but
> #parse.  However, I tried the and it seems that it only works for certain
> directives, eg  #foreach, #include, etc.  More basic directives like #if
> and #elseif are not in the list of runtimedirectives, or even represented
> as Directive objects, so removing them doesn't work.

Yeah, they are deep in the parser.  Their structure doesn't work as a
normal directive.

> Any suggestions on the best way to proceed with this? Would it be easy to
> change a few velocity files locally, recompile and get this behavior? Or is
> it sufficiently complex removing all these more basic directives that I'm
> better off continuing to try some kind of  preprocessing/ escaping?

You would have to redesign Velocity's parsing deeply.  A major
overhaul.  You're best off preprocessing.   Have you considered using
a different template engine to do the first part (the parse and
resourceBundle resolution)?  Might be overkill, but might be easier,
so long as the syntax has no overlap with VTL.

> thanks,
> Pete