Merging Velocity Output w/ Existing File

["Stratton, Jason" <Ja...@us.ing.com>]

Hi All,

I have been using Velocity to generate files and it has been working quite well for me. Thank you.

Now I have been asked to look at the ability to merge the output from Velocity with the existing files. To clarify, when my tool is run once and the files have been generated, the user will potentially change the files and we do not want to lose the changes when Velocity is run again. Right now the Velocity output overwrites the files. It is understood that only the static content in the files can possibly be preserved.

My questions are:
- Is this possible/practical with Velocity?
- If not, is there another technology that I should investigate?

Thank you very much.
Jason

Re: Merging Velocity Output w/ Existing File

[Dave Newton <da...@solaraccess.com>]

On Tue, 2003-09-09 at 13:16, Stratton, Jason wrote:
> Now I have been asked to look at the ability to merge the output 
> from Velocity with the existing files. To clarify, when my tool
> is run once and the files have been generated, the user will
> potentially change the files and we do not want to lose the changes
> when Velocity is run again. Right now the Velocity output overwrites
> the files. It is understood that only the static content in the files
> can possibly be preserved.

I'm not sure what you mean.

If there are chunks in the output file that a user can change and then
you want to run velocity but not lose those changes then maybe you
should consider a two-step velocity process so that the velocity chunks
are inserted into a different template; the one the user can change.

I use this technique in a few places, for instance, I create a dynamic
email which is then merged with the mailing list (so the first velocity
run is actually creating a velocity template that is used in the
mailmerge)

Dave

Re: Merging Velocity Output w/ Existing File

[Mike Kienenberger <mk...@alaska.net>]

"Stratton, Jason" <Ja...@us.ing.com> wrote:
> Hi All,
> 
> I have been using Velocity to generate files and it has been working quite 
well for me. Thank you.
> 
> Now I have been asked to look at the ability to merge the output from 
Velocity with the existing files. To clarify, when my tool is run once and 
the files have been generated, the user will potentially change the files 
and we do not want to lose the changes when Velocity is run again. Right now 
the Velocity output overwrites the files. It is understood that only the 
static content in the files can possibly be preserved.
> 
> My questions are:
> - Is this possible/practical with Velocity?
> - If not, is there another technology that I should investigate?
> 
> Thank you very much.
> Jason

It depends on the details.

If you're generating java code, you can generate things in a "Gap 
Generation" design patern

public class GENERATED_SUPERCLASS // generated by Velocity every time.
{
}

public class MY_CLASS extends GENERATED_SUPERCLASS // generated by Velocity 
only if it doesn't exist
{
}

Other possiblities including using #include to include the static content.

Idealistically, your users should be changing the templates, not the 
generated files....

Of course, it may not be possible in your environment, but if that's the 
case, no template engine will probably be any better.

-Mike