Gist for creating Dex file for class files in Android Library

build.gradle

/**
 * The Task Below uses the Dex Tool to create classes.dex file for the archive
 * This dex file can be then be loaded at runtime to prevent the 64K Dalvik Method Limit
 */
import org.apache.tools.ant.taskdefs.condition.Os
android.libraryVariants.all { variant ->
    def name = variant.buildType.name
    if (name.equals(com.android.builder.BuilderConstants.DEBUG)) {
        return; // Skip debug builds.
    }

    log.info("========================================")
    log.info("Starting Variant Build")
    log.info("Variant Name: ${variant.name}")
    log.info("Build Type Name: ${variant.buildType}")
    log.info("Variant: ${variant}")
    log.info("========================================")

    String cmdExt = Os.isFamily(Os.FAMILY_WINDOWS) ? '.bat' : ''
    def task = project.tasks.create ("dex${name.capitalize()}", Exec)

    task.dependsOn variant.javaCompile
    task.commandLine "${System.env.ANDROID_HOME}/build-tools/${BUILD_TOOLS_VERSION}/dx${cmdExt}", '--dex',
            "--output=${buildDir}/classes/${variant.name}/classes.dex",
            "${buildDir}/classes/${variant.name}"

    // Make sure we run our Dexing task before the packageReleaseJar Task
    Task packageJar = project.tasks.getByName("package${name.capitalize()}Jar")
    packageJar.dependsOn(task)
}