Proguard在非Android项目中使用Gradle的问题

我试图用Proguard混淆我的Java项目的代码.该项目已在Intellij上创建,并使用Gradle 2.2.1进行配置.我工作的计算机上有一个代理,因此Intellij无法访问Internet.

我试了几个小时找到一个简单的例子来混淆我的代码.

我试着这样做:

task proguardTask(type: proguard.gradle.ProGuardTask) { println "ha"}
task proguardTask(type: proguard.gradle.ProGuardTask) <<{ println "ha"}

我每次都得到一个例外:

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':proguardTask'.
> Index: 0, Size: 0
java.lang.IndexOutOfBoundsException: Index: 0, Size: 0
        at proguard.ClassPath.get(ClassPath.java:77)

这是我的build.gradle文件:

// Configuration des library java
project.ext.LIBJava = [
        "project1",

        "project2", "project2",
        "project2_OS", "project2_UI",
        "project3",
        "project3_Windows"
]

//----------------------------------------------------------------------------------------------------------

ext.buildOnline= false
ext.buildOnlineMapsforge= false
ext.buildAndroid = false

//----------------------------------------------------------------------------------------------------------

apply plugin: 'idea'
apply plugin: 'eclipse'
apply plugin: 'java'

buildscript {
    repositories {
        mavenLocal()
        mavenCentral()
        flatDir dirs: 'C:/Path/To/Proguard/proguard-5.1/lib'
    }
    dependencies {
        classpath ':proguard'
    }
}

def filterProjects(filter) { return subprojects.findAll { project -> filter.contains(project.name) } }


allprojects {
    group = 'org.libWin'
    version = '0.1.1'
}

// Configuration injection for all subprojects
subprojects {
    repositories {
        mavenLocal()
        mavenCentral()
    }
}

//----------------------------------------------------------------------------------------------------------

task proguardTask(type: proguard.gradle.ProGuardTask) {
    println "ha"
}

configure(filterProjects(project.LIBJava)) {
    apply plugin: 'java'

    dependencies {
        if (buildOnline) { // On-line
            testCompile group: 'junit', name: 'junit', version: 4.11           //  "$jUnitVersion"
        }
    }

    [compileJava, compileTestJava]*.options*.encoding = 'UTF-8'
}

有谁知道问题的来源？如何使用Gradle使用Proguard轻松混淆我的代码？

谢谢.