How to change java.srcDirs in gradle sourceSets dynamically?

Question

By default, thejava.srcDirs in sourceSets is declare like the following:

android {
    sourceSets {
        gdt{
            java.srcDirs = ['src/gdt/java']
        }
        open {
            java.srcDirs = ['src/open/java']
        }
    }
}

How to change it dynamically.

...What i wanna do is to select different files to build an aar according to the input from command line.

Any better idea for achieving this？