同时使用parceler/butterknife/dagger2出现DuplicateFileException的解决方法

　同时使用parceler、butterknife和dagger2这几个库时，可能是因为都用到了annotation，gradle报错：

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Error:Execution failed for task ':app:transformResourcesWithMergeJavaResForDebug'.

> com.android.build.api.transform.TransformException: com.android.builder.packaging.DuplicateFileException: Duplicate files copied in APK META-INF/services/javax.annotation.processing.Processor

File1: C:\Users\xxx\.gradle\caches\modules-2\files-2.1\org.parceler\parceler\0.2.16\37438b5c380d8eb22bd3ae616077561b7f906ff3\parceler-0.2.16.jar

File2: C:\Users\xxx\.gradle\caches\modules-2\files-2.1\com.jakewharton\butterknife\7.0.1\d5d13ea991eab0252e3710e5df3d6a9d4b21d461\butterknife-7.0.1.jar

　　解决方法为，在build.gradle中加入packagingOptions排除annotation，annotation不需要被打包进APK：

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android {

    ...

    packagingOptions {

        exclude 'META-INF/services/javax.annotation.processing.Processor'

    }

}