Gradle: Plugin with id appengine not found - google-app-engine

Question

I m working on Mac, with Android Studio.
I m trying to build a Android App with a Google App Engine BackEnd.
I've installed Maven and Gradel and exported the M2_HOME et GRADLE_HOME
Whenever I run any of the Gradle commends I get this :
Error:(21, 0) Gradle: A problem occurred evaluating project
':backend'. Plugin with id 'appengine' not found.
the Build.gradle file :
buildscript {
repositories {
mavenCentral()
}
dependencies {
}
}
repositories {
mavenCentral()
}
apply plugin: 'java'
apply plugin: 'war'
apply plugin: 'appengine'
sourceCompatibility = 1.7
targetCompatibility = 1.7
dependencies {
appengineSdk 'com.google.appengine:appengine-java-sdk:1.9.3'
compile 'javax.servlet:servlet-api:2.5'
compile 'com.googlecode.objectify:objectify:5.0.+'
compile 'com.google.guava:guava:16.0.+'
}
appengine {
downloadSdk = true
appcfg {
oauth2 = true
}
}

Answer 1

From description on plugin github page you need to define plugin JAR file in the classpath of your build script.
So here is how it can be done:
buildscript {
repositories {
mavenCentral()
}
dependencies {
classpath 'com.google.appengine:gradle-appengine-plugin:1.9.3'
}
}
....