Creating ant build script to build only when a dependency was updated

I just started working with ant a few days ago. Right now I have a general buildall.xml which should c开发者_StackOverflow中文版all each project's build.xml. Because some projects depend on each other, I need to rebuild some other projects which depend on it. This isn't a problem--I'm just setting the depends property of the target. However, ant is always building the dependencies, even when the files haven't changed.

Let's say project1 has no dependencies; project2 depends on project1; project3 depends on project1, 2; project4 depends on project1, 2, and 3; and so on.

I could hack a solution which looks at project K, and checks if project 1 .. project K have updated files using uptodate. If so, then run the target. This is messy and appears unnecessary.

What is the cleanest way to implement this?

EDIT: So I decided to just hack in a bunch of targets, "check_projectK" where it does the uptodate checks on all of its source files, its build file, and the build files of the 1 .. K-1 projects. Due to dependencies, this is always handled correctly. However, this is still a large amount of copy and paste for a large workspace. I will leave this open.

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Short answer, ANT can't do it, not unless you have some kind of way to connect to your version control system and check if anything has changed (you are using source control right?). Ant doesn't know about when what the last time a file changed and then see if it matches with what was built; it doesn't have the concept of a dependency repository. The whole purpose of Ant is that it just builds.

The solution to your problem isn't Ant, it's Maven. Maven HAS a dependency repository. There's also a very nifty plugin for Maven used specifically with Flex appropriately called FlexMojos. By using this, Maven can know when something was last built because it's uploaded to the repository. Then your other projects can add it's dependencies and download the SWC needed.

On top of that, it mixes great with a continuous integration engine like Hudson, Bamboo and Teamcity, which builds a project every time a file has been committed to your source control system, and then updates all dependent projects automatically!