Here's a suggestion for a new feature in Ant. I would like to see the
capability for a "default" or dynamic target in Ant. What this would do is
catch all target invocations (or target invocations based on a pattern) after
all explicit targets have been matched. In other words, any targets which now
error out for "target not found" would instead be caught and processed by the
default target.
This is useful for something I'm experimenting with now - dynamic generation of
Ant scripts. In my current project, developers are using different sets of app
servers, each with not only different config values, but with totally different
config parameters sets. Each developer has a different setup, so it is
difficult to write a single Ant file to handle them all, and local changes by
each developer can't be effectively version controlled. (Yes, I know the flaw
in this environment, but I can't control it.)
My experimental solution is to have each developer create a local app server
definition file, which I then apply a set of XSLT sheets to in order to create
an Ant script.
Easy enough so far. The complication comes in when I have a master script to
do the XSLT transforms and then call the generated script. The way Ant is
structured today, the sub-targets will have to be explicitly coded into the
master script in order to have it call the sub-script. I can work around this
by having the developers call the generated script directly with -buildfile,
but I want to avoid this if possible.
So, my proposed solution goes like this. Assume we have a build script like
this:
<target name="target-1">
...
</target>
<target pattern="target-*">
...
</target>
<default-target>
...
</default-target>
Then target invocations would match up like this:
"ant target-1" would invoke target-1, since there is an explicit match.
"ant target-2" would invoke target-*, since there is no explicit match, but
there is a pattern match.
"ant my-target" would invoke the default target, since there is no explicit or
pattern match.
(Let me point out here that pattern targets and default targets are related,
but separate ideas and don't need to be implemented together. I think default
targets would be the simpler and more useful to implement first.)
Now I'll show how this relates to my situation. My master script has a number
of generic targets - the compilation, jars, etc. But I also want it to be able
to pass unknown targets on to the sub-script for processing there. So, imagine
that my master script looks like this:
<target name="compile">
...do some stuff...
</target>
<default-target>
<ant antfile="servers.xml" target="${target.name}"/>
</default-target>
where "target.name" is a property set by the default-target class, containing
the name of the target that was invoked (and fell through to the default
target).
Now, in my sub-file, I have the following:
<target name="deploy-local">
...
</target>
<target name-"deploy-remote">
...
</target>
So, now, an invocation of "ant deploy-local" will be unsatisfied in the main
script and will fall through to the default target. This will invoke the
sub-script, which has a matching target. An invocation of "ant dummy-target"
will fall through the first script to the default target and flow to the
sub-script which also has no match, so we get the usual "target not found"
error.
Without this sort of capability today, I have to resort to something like Perl
scripts to straighten out where each target should go. I would like to have
all of this native to Ant if possible.
For those of you who will answer by saying I shouldn't be generating dynamic
scripts - I get the point, but some situations call for it, and believe me,
it's easier than teaching every developer on the project how to write their own
scripts. (And better than having them spend expensive time on it...)
Any comments would be appreciated.
Roger Vaughn
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