Error:Execution failed for task ‘:app:proguardDemoRelease‘.
> java.io.IOException: The same input jar [D:\Users\workspace_studio\Test5\app\libs\fastjson.jar] is specified twice.
解决方案：
删除 -libraryjars libs/***.jar from your proguard-rules.pro file.
原因是build.gradle文件配置了
dependencies { compile fileTree(include: ‘*.jar‘, dir: ‘libs‘)
}
里面已经添加过jar包，混淆文件proguard-rules.pro里面又加了句-libraryjars libs/***.jar,将-libraryjars libs/***.jar 前面用#号注释或者直接删掉即可。
Eclipse混淆文件导入Android Studio Gradle编译报input jar file is specified twice
原文：http://blog.csdn.net/x_i_a_o_h_a_i/article/details/41979983
