Error:Execution failed for task ':app2: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 annotationProcess
出现这种错误 ，在app下Build. gradle里面加如下代码就行
defaultConfig {
javaCompileOptions
{ annotationProcessorOptions { includeCompileClasspath = true } }