后来自己写了task，实现了这个功能

jar {
    String someString = ''
    configurations.runtime.each {someString = someString + " lib//"+it.name}
    manifest {
        attributes 'Main-Class': 'cc.gnaixx.tools.core.Hidex'
        attributes 'Class-Path': someString
    }
}

task clearPj(type:Delete){
    delete 'build','target'
}

//copy 运行时依赖
task copyJar(type:Copy){
    from configurations.runtime
    into ('build/libs/lib')
}

task release(type: Copy,dependsOn: [build,copyJar]) {
    //
}

在依赖这个jar的工程中的build.gradle文件中依赖一下fastjson，如

dependencies {
    compile 'com.alibaba:fastjson:1.2.13'
}