`即使使用默认目录结构,gradlew run也找不到主kotlin类

我的项目 gradle/kotlin 目录结构遵循默认/推荐的方法:

MYPROJ
      /src/main/kotlin
                       app/OnsetsWebapp.kt

这是 build.gradle.kts :我们指定的通知 mainClassName = app.OnsetsWebapp :

plugins {
  application
  kotlin("jvm") version "1.3.71"
}

application {
  mainClassName = "app.OnsetsWebapp"
}

dependencies {
  compile(kotlin("stdlib"))
  compile("org.slf4j:slf4j-simple:1.7.25")
  compile("io.javalin:javalin:3.8.0")
  compile("org.json:json:20160810")
  compile("com.j2html:j2html:1.3.0")
}

repositories {
  jcenter()
}

让我们构建它: ./gradlew build

BUILD SUCCESSFUL in 1s
8 actionable tasks: 5 executed, 3 up-to-date

现在让我们运行它:

 $./gradlew run

这导致

> Task :run FAILED
Error: Could not find or load main class app.OnsetsWebapp
Caused by: java.lang.ClassNotFoundException: app.OnsetsWebapp

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':run'.
> Process 'command '/Library/Java/JavaVirtualMachines/openjdk-11.0.2.jdk/Contents/Home/bin/java'' finished with non-zero exit value 1

* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.

* Get more help at https://help.gradle.org

BUILD FAILED in 0s
4 actionable tasks: 1 executed, 3 up-to-date

那么为什么这个班 app.OnsetsWebapp 未找到?