Android studio 引用 butterKnife包错误解决

 错误提示：

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-compiler-8.8.1.jar (com.jakewharton:butterknife-compiler:8.8.1)
  Alternatively, set 

提示：工程里的module依赖了butterknife的jar包，而jar里面又用到了注解。在新的gradle版本里，需要写新的groovy代码来对每个引用注解的地方单独配置。 
而在以往的版本中，gradle会默认给每个module都依赖一个annotationProcess，导致很多多余的对annotationProcess的依赖。
 

方案（一）：在相应的module的gradle文件中，使用javaCompileOptions

defaultConfig {
        applicationId "com.breakloop.httpurlconnectiondemo"
        minSdkVersion 15
        targetSdkVersion 26
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
        //添加了javaCompileOptions 
        javaCompileOptions {
            annotationProcessorOptions {
                includeCompileClasspath = true
            }
        }
    }

方案（二）：在相应的module的gradle文件中，使用annotationProcessor

dependencies {
    compile fileTree(include: ['*.jar'], dir: 'libs')
    androidTestCompile('com.android.support.test.espresso:espresso-core:2.2.2', {
        exclude group: 'com.android.support', module: 'support-annotations'
    })
    compile 'com.android.support:appcompat-v7:26.+'
    compile 'com.android.support.constraint:constraint-layout:1.0.0-alpha7'
    testCompile 'junit:junit:4.12'
    implementation 'com.jakewharton:butterknife:8.8.1'
    implementation 'com.jakewharton:butterknife-compiler:8.8.1'
    //添加了annotationProcessor
    annotationProcessor "com.jakewharton:butterknife-compiler-8.8.1"
}

然后项目就构建成功了。