Is Maven really flexible? - maven

Question

I understand how Maven works with .java files in src/java/main. But may it be used for a more general case? Let us put it more abstract: Suppose I already have some a.exe that reads some (not necessarily only .java) sources from directories A1, A2, A3 and puts some files (maybe some are generated .java) to directories B1, B2. I also have some b.exe that currently reads files from B1, B2, B3 and generates something else. Some more similar steps. (A real life problem stands behind).
I would like to write a POM.xml file so that maven will do this work. Is that possible? I assume that a.exe and b.exe should be warped as maven plugings.
Next, in Maven docs I see :
<build>
<sourceDirectory>${basedir}/src/main/java</sourceDirectory>
<scriptSourceDirectory>${basedir}/src/main/scripts</scriptSourceDirectory>
<testSourceDirectory>${basedir}/src/test/java</testSourceDirectory>
<outputDirectory>${basedir}/target/classes</outputDirectory>
<testOutputDirectory>${basedir}/target/test-classes</testOutputDirectory>
...
</build>
What bothers me is that "sourceDirectory" looks by itself as a hard coded name. Will Maven accept A1 and A2 tags instead?

Answer 1

(Will you consider accepting some of your previous questions, so that other people will be more willing to answer you?)
Maven stress for Convention over Configuration. You can treat sourceDirectory as one of the conventions, which we have predefined some elements to use with the (Java) compiler plugin.
What you want to do can be achieved. You can write a plugin/MOJO yourself, which read from whatever directory you want and invoke whatever external exe you want. By having reasonable default values in your MOJO, you can have your project POM look something like
<project>
:
:
<build>
<plugins>
<plugin>
<groupId>yourPluginGroup</group>
<artifactId>generate-A-data</artifactId>
<!-- if you want extra configuration, you can have <configuration> elements -->
</plugin>
<plugin>
<groupId>yourPluginGroup</group>
<artifactId>generate-B-data</artifactId>
</plugin>
</plugins>
</build>
<project>
Not that bad huh?
However, it is quite questionable to say whether Maven is "flexible". I believe flexibility is never the aim of Maven. Maven is specialized for building, it defines different skeletons for you to follow (e.g. build phases, dependency scopes), you can never make Maven as "flexible" as other script-based tools like Ant.

Answer 2

The answer is: NO, MAVEN IS NOT FLEXIBLE. Here is a simple task I could not solve even with the help from all the maven forums of this world: Write a POM that
compiles some directory full of Java files
does something else (if you please - executes a sample Hello World Mojo plugin)
compiles some other directory with some other Java files.
NO WAY !

Answer 3

You may be able to do this without writing plugins, by binding the exec plugin and the compiler plugin to the 'generate-sources' or 'process-classes' phases. The build helper plugin might also be useful for adding source paths.
For the original case, you could try the following bindings:
build-helper-maven-plugin bound to the initialize phase, adding any necessary source directories (eg B1 and B2)
exec-maven-plugin bound to the generate-sources phase, with two executions, one for a.exe and one for b.exe
For the Hello World Mojo case, what if you add the following to the process-classes phase (in order)?
Hello World Mojo plugin
Build Helper plugin to add source directory
Compiler plugin
The only downside I can see is that the first source directory will be recompiled. But the compiler should be smart enough to know that nothing has changed, and whether it's a problem depends on why you actually want to do this. Why do you need the class files from directory A before you run Hello World? Perhaps you're really looking at two separate pieces of code that should become separate modules?