app:javaPreCompileDebug和transformDexArchiveWithExternalLibsDexMergerForDebug

出现这个错误之后在App的build.gradle(Module：app)

Error:Execution failed for task ‘:app:javaPreCompileDebug’.
> Annotation processors must be explicitly declared now.  The following dependencies on the compile classpath are found to contain annotation processor.  Please add them to the annotationProcessor configuration.
    – butterknife-7.0.1.jar (com.jakewharton:butterknife:7.0.1)
  Alternatively, set android.defaultConfig.javaCompileOptions.annotationProcessorOptions.includeCompileClasspath = true to continue with previous behavior.  Note that this option is deprecated and will be removed in the future.
  See https://developer.android.com/r/tools/annotation-processor-error-message.html for more details.

在app的build中

android {

    …
    defaultConfig {

        …
        //添加如下配置就OK了
        javaCompileOptions { annotationProcessorOptions { includeCompileClasspath = true } }
    }
    …
}

但是紧接着build后又出现Error:Execution failed for task ‘:app:transformDexArchiveWithExternalLibsDexMergerForDebug

最终在这里找到答案 http://it72.com/thread-12286.htm

查了下也没发找到答案，什么删除.gradle重新clean没用，

Clean Project 和Rebuild Project全都没有用，删除.idea和其它配置，重新导入工具再编译一样没用，最后看到一篇文章，说是.jar包重复，说是去掉就可以解决。但我工程里面是没有重复引用的jar库，但是真的是解决了。打开工程的依赖项，删除里面的项包support:appcompat-v7就行了

出现问题自己先找问题，这种异常不是配置文件丢失，或者就是依赖 及Jar重复，总之细心规范编程，养成良好的习惯！

书到用时方恨少，纸上得来终觉浅，希望对您有所帮助！