Selective dependencies in Gradle - gradle

Question

I'm setting up a multi-project Gradle build to replace an existing Ant build, where all the sub projects have their own build.gradle file in which the sub-project's dependencies are defined.
My sub projects all have their own dependencies, and there's a small subset of those (all 3rd party jars) that are only needed as a compile-time dependency in all the sub projects, like Maven's provided scope. (I have already found how I can create a configuration in Gradle that behaves like that.)
However, since this is a small set of jars, and they're the same for all sub projects, I'd like to extract the knowledge of which jars are provided out of the individual sub projects's dependency lists, and into the main build script, somehow. I want this so that developers who add a sub project to the system, don't need to know about which dependencies are provided and which aren't.
In other words, I would like to have a configuration that behaves as provided for a specific list of dependencies, and as compile for all the others.
I have this in the main build.gradle:
ext.providedDependencies = [
"org.apache.log4j:log4j:1.2.16",
"joda-time:joda-time:2.0"
]
...
configurations { myconfig }
And one or more of the sub projects have a build.gradle like this:
dependencies {
myconfig "org.apache.log4j:log4j:1.2.16"
myconfig "org.apache.commons:commons-lang3:3.3.2"
}
Then I want the behavior to be like this:
dependencies {
provided "org.apache.log4j:log4j:1.2.16"
compile "org.apache.commons:commons-lang3:3.3.2"
}
Because log4j is in ext.providedDependencies, and commons-lang3 isn't. I want this same behavior for all of my subprojects.
I have tried to (partially) implement myconfig like this:
subprojects {
dependencies {
configurations.myconfig.dependencies.each { dep ->
if (providedDependencies.contains(dep)) {
compile dep
}
}
}
}
But that does not work, because it turns out that configurations.myconfig.dependencies is empty (I don't understand why, though). In other words, the dependencies don't get added.
I also tried this, but here the opposite happens: all the dependencies are added, including those that are in the list of provided dependencies.
subprojects {
dependencies {
compile(configurations.myconfig) {
providedDependencies.each { exclude it }
}
}
}
Please let me know how I can make this work, or if there is a different, better way to achieve what I want.
EDIT Partially re-written for clarity

Answer 1

ext{
dependencies = [
"dependencyGroup:dependencyName:dependencyVersion",
"dependency2Group:dependency2Name:dependency2Version"
]
}
subprojects{
dependencies {
provided dependencies
}
configurations {
compile.exclude group: 'dependencyGroup'
compile.exclude group: 'dependency2Group'
}
}
In the above example, we have defined a list of dependencies with the name dependencies.
EDIT -- We are excluding the dependencies from the compile configuration if they need to be provided. This means that all even if a subproject adds a dependency that you want to be provided as compile, it won't happen.