Simple gradle proguard task for use with the java-plugin.

proguard_build.gradle

ant.taskdef(resource: 'proguard/ant/task.properties',
            classpath: "/usr/local/java/proguard/lib/proguard.jar")

task proguard << {
    description = "Process classes and JARs with ProGuard"
    group = "ProGuard"

    def proguardDir = new File(getProguardDir(project))
    proguardDir.mkdir()

    ant.proguard(configuration: project.ext.proguardConfig,
                 printmapping: project.ext.proguardMapping) {

        libraryjar(file: project.ext.proguardLibraryjar)
        injar(file: project.ext.proguardInjar, filter: '!META-INF/**')
        outjar(file: project.ext.proguardOutjar)
    }

    ant.move(file: project.ext.proguardOutjar, toFile: project.ext.proguardInjar, overwrite: true)
}

def getProguardDir(project) {
   return "$project.buildDir/proguard"
}