Obfuscate a jar with Gradle

obfuscate.gradle

ext {
  mainClassName = "foo.bar.buz.mainClass"
  basename = "fooBar"
  version = "42.0"
}

task obfuscate(type: proguard.gradle.ProGuardTask) {
  injars "./build/libs/${basename}-${version}.jar"
  outjars "./build/libs/${basename}-${version}-obf.jar"

  libraryjars "${System.getProperty('java.home')}/lib/rt.jar"

  dontwarn
  overloadaggressively
  repackageclasses 'foo'
  printmapping "./build/libs/${basename}.map"

  keep 'class !foo.bar.buz**,!foo.bar.baz.** { *; }'

  keepclasseswithmembers "public class ${mainClassName} { \
    public static void main(java.lang.String[]); \
  }"

  keepclassmembers allowshrinking:true, 'enum * { \
    public static **[] values(); \
    static boolean contains(java.lang.String); \
  }'

} 

@maru2213 sound like you haven't include proguard as a dependance in your gradle file

Add this line to the beginning of your gradle file. @maru2213

buildscript {
    repositories {
        mavenCentral()
    }
    dependencies {
        classpath 'net.sf.proguard:proguard-gradle:5.3.3'
    }
}