how to configure the plugin to apply on a specific directory of classes?

[aminabs]

Hi, I want to know if there is a way to configure input directory for the retrolambda plugin. It seems to me its not configurable since I can't see any info about it on the home page. To elaborate, please take a look at the retrolambda maven plugin here where you see an option 'retrolambda.inputDir' available for doing so.

[sriharshachilakapati]

I had this exact same issue (I wanted to use libraries which are compiled with Java 8) and I have solved this by making the retrolambda tasks depend on a custom task which extracted the required classes into the javaCompile output directory (build/retrolambda/$variant) so retrolambda will also transform the library classes and this worked beautifully.

// I have the java 8 dependencies as 'provided' scope, so the dex compiler will
// not complain about them. This task occurs before retrolambda and extracts
// them into the retrolambda's input directory.
task beforeRetrolambda << {
    copy {
        // Copy all the classes in debug config
        configurations.provided.asFileTree.each {
            from(zipTree(it))
        }
        into 'build/retrolambda/debug/'
        include '**/*.class'
    }

    copy {
        // Copy all the classes in release config
        configurations.provided.asFileTree.each {
            from(zipTree(it))
        }
        into 'build/retrolambda/release/'
        include '**/*.class'
    }
}

// Hook them to retrolambda, so you get transformed classes for the libraries.
afterEvaluate {
    compileRetrolambdaDebug.dependsOn beforeRetrolambda
    compileRetrolambdaRelease.dependsOn beforeRetrolambda
}

Retrolambda now assumes that all these classes are from your android application module, and includes them in dex file and the apk. This is how it worked for me.