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

1. Android Studio 编译时报错如下：

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.

2. 解决方式

在 app 项目目录中的 build.gradle 文件中，找到 defaultConfig 并在这个方法里面添加如下代码：

    javaCompileOptions {
        annotationProcessorOptions {
            includeCompileClasspath true
        }
    }