Replacing build.xml with Build.java - using Java and the Ant libraries as a build system

Question

I've grown disillusioned with Groovy based alternatives to Ant. AntBuilder doesn't work from within Eclipse, the Groovy plugin for Eclipse is disappointing, and Gradle just isn't ready yet.

The Ant documentation has a section titled "Using Ant Tasks Outside of Ant" which gives a teaser for how to use the Ant libraries from Java code. There's another example here:

http://www.mail-archive.com/dev@ant.apache.org/msg16310.html

In theory it seems simple enough to replace build.xml with Build.java. The Ant documentation hints at some undocumented dependencies that I'll have to discover (undocumented from the point of view of using Ant from within Java).

Given the level of disappointment with Ant scripting, I wonder why this hasn't been done before. Perhaps it has and isn't a good build system.

Has anyone tried writing build files in Java using the Ant libraries?

Answer 1

Our build system is primarily based upon exactly what you describe, and it works very well indeed. We use the Ant tasks (especially the file-manipulation tasks) from custom java programs which assemble the application using auto-discovery of convention-based application module layout.

You may need some glue Ant XML, to do things like compile the build scripts themselves, and to actually invoke the java to perform the build, but it's minor.

Not only is java more readable than Ant, especially when it comes to conditional execution, but it's vastly quicker. Our Ant-based build used to take a minute or so to assemble an EAR, now the java based version takes about 5 seconds.

Answer 2

You had a fine idea. Cliff Click had a similar idea: http://blogs.azulsystems.com/cliff/2008/01/i-hate-makefile.html

If you go through with it I advise you to keep it as simple as possible so your build system doesn't need a [non-trivial] build system itself.

Answer 3

Given that Java is compiled, this is kind of a chicken and egg problem. You need to build your Build.java to build your project.

Ant currently supports inline scripting using BeanShell, Groovy and a bunch of others, that can really help reduce the need for that.

EDIT: In response to Dean's multiple comments, if your build consists strictly of a long proceedure, then indeed you don't need ant's build script. However, the power of the build script is that it ensures that dependencies are only executed once while allowing for mulitiple entry points, something that is far from trivial if you roll your own.

If you don't like the XML format, you are not alone, the author of ANT agrees with you. However, if your view of the build process is something that can be launched from your IDE as its only launch point, I would say that your build needs are quite simple.

EDIT2: I upvoted skaffman's answer because it speaks directly to the question. In the comments we seem to agree that the approach is fine for a procedural build, but would not work for a declarative one, and that you need at least a little ANT xml to get the ball rolling with your Build.java to avoid the chicken and egg problem. That seems to get to the crux of the matter.

Answer 4

An important point seems to have gotten lost here.

Ant is written in Java and what I'm looking for is a better way to use the Ant tasks (APIs in the Ant libraries) than through xml. For the life of me I can't see how using xml to invoke Java would ever be better or easier than using Java to invoke Java.

The one obstacle is that the xml approach is documented whereas the Java approach is not documented so I'll have to download and get familiar with the Ant code.

I held back from posting this question for a couple of weeks because I was sure that someone had done this before and that my google-foo just needed improving. It just seems so obvious to use Java to call the Ant APIs instead of xml that I'm still surprised that there wasn't a parallel Java-based approach developed for Ant as well as the xml approach.

Just because it is obvious doesn't mean that someone has done it before, though.

Answer 5

While I suppose its possible, you would probably be better off with shell scripts then writing a full on java program to simply automate builds.

You would be missing out on one of the key uses for ant, which are the easy-to-specify filesets and easy to read in properties.

I have stuck with ant as Groovy is too close to writing an entire application to just build your real application. Too complicated for the trouble.

Answer 6

While using Ant tasks inside Java programs is fairly easy, I probably would stick to Ant build files if I were you. If you're doing some groovy development, if Eclipse doesn't do what you need, maybe you need to look elsewhere(IntelliJ, NetBeans, etc.).