Using annotation processing in gradle

build.gradle

buildscript {
    repositories {
        mavenCentral()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:0.5.+'
    }
}
apply plugin: 'android'

repositories {
    mavenCentral()
}

configurations {
    apt
}

dependencies {
    compile 'com.android.support:support-v4:13.0.+'
    compile 'com.google.android.gms:play-services:3.1.+'
    compile 'com.jakewharton:butterknife:2.0.+'
    apt 'com.jakewharton:butterknife:2.0.+'
}

android {
    compileSdkVersion 17
    buildToolsVersion "17.0.0"

    defaultConfig {
        minSdkVersion 8
        targetSdkVersion 16
    }
}

android.applicationVariants.each { variant ->
    ext.aptOutput = file("${project.buildDir}/source/apt_generated/${variant.dirName}")
    
    variant.javaCompile.doFirst {
        aptOutput.mkdirs()
        variant.javaCompile.options.compilerArgs += [
                '-processorpath', configurations.apt.getAsPath(),
                '-s', aptOutput
        ]
    }
}