android.applicationVariants.all { variant ->

        variant.outputs.each { output ->

            def outputFile = output.outputFile

            if (outputFile != null && outputFile.name.endsWith('.apk')) {

                //在这里修改apk文件名

                def fileName = "想要的文件名.apk"

                output.outputFile = new File(outputFile.parent, fileName)

            }

        }

}

android.applicationVariants.all {

    variant ->

        variant.outputs.all {

            //在这里修改apk文件名

            outputFileName = "${variant.name}-v${variant.versionName}.apk"

        }

}