Is there an ANT task for watching a directory for changes? - ant

Question

It sounds a little far fetched to me, but is there an ANT task for watching a directory for changes and then running a particular ANT class when the directory changes?

Answer 1

If files can only be added to or changed in the watched directory, then you can use this simple OutOfDate task from antcontrib.
<property name="watched-dir.flagfile"
location="MUST be not in watched dir"/>
<outofdate>
<sourcefiles>
<fileset dir="watched-dir"/>
</sourcefiles>
<targetfiles>
<pathelement location="${watched-dir.flagfile}"/>
</targetfiles>
<sequential>
<!--Tasks when something changes go here-->
<touch file="${watched-dir.flagfile}"/>
</sequential>
</outofdate>
If files can disappear from the watched-dir, then you have more complicated problem, that you can solve by creating shadow directory structure of the watched dir and checking if its consistent with the watched-dir. This task is more complex, but I'll give you a script to create a shadow directory, as it is not straight forward:
<property name="TALK" value="true"/>
<property name="shadow-dir"
location="MUST be not in watched dir"/>
<touch
mkdirs="true"
verbose="${TALK}"
>
<fileset dir="watched-dir">
<patterns/>
<type type="file"/>
</fileset>
<!-- That's the tricky globmapper to make touch task work -->
<globmapper from="*" to="${shadow-dir}/*"/>
</touch>
<!--
Due to how touch task with mapped fileset is implemented, it
truncates file access times down to a milliseconds, so if you
would have used outofdate task on shadow dir it would always
show that something is out of date.
Because of that, touching all files in ${shadow-dir} again fixes
that chicken and egg problem.
-->
<touch verbose="${TALK}">
<fileset dir="${shadow-dir}"/>
</touch>
With shadow directory created, I'll leave the task of checking directory consistency as an exercise for the reader.

Answer 2

Yes there is an Ant Task that will do this:
https://github.com/chubbard/WatchTask
It requires 1.7+. It can watch any number of filesets, and invoke any target depending on which fileset it came from.

Answer 3

You might be able to use the Waitfor task to achieve what you want. It blocks until one or more conditions (such as the presence of a particular file) become true.

Answer 4

You can combine the apply task with a fileset selector
<apply executable="somecommand" parallel="false">
<srcfile/>
<fileset dir="${watch.dir}">
<modified/>
</fileset>
</apply>
The fileset will check the files against a stored MD5 checksum for changes. You'll need to put ANT into a loop in order to repeatedly run this check. this is easy to do in Unix:
while true
> do
> ant
> sleep 300
> done