生产环境下Play Framework读取public目录静态文件异常问题

基本信息 #

• 静态文件路径：public/robots.txt
• 访问地址：http://localhost:9000/robots.txt
• 预期：正常加载文件无错误
• 现状：本地运行正常，Docker部署后访问抛出异常

报错日志 #

[error] a.a.OneForOneStrategy - null
java.lang.NullPointerException: null
    at kamon.instrumentation.akka.instrumentations.akka_26.InstrumentNewExecutorServiceOnAkka26$.around(DispatcherInstrumentation.scala:109)
    at akka.dispatch.ThreadPoolConfig$ThreadPoolExecutorServiceFactory.createExecutorService(ThreadPoolBuilder.scala)
    at akka.dispatch.Dispatcher$LazyExecutorServiceDelegate.executor$lzycompute(Dispatcher.scala:44)
    at akka.dispatch.Dispatcher$LazyExecutorServiceDelegate.executor(Dispatcher.scala:44)
    at akka.dispatch.ExecutorServiceDelegate.execute(ThreadPoolBuilder.scala:219)
    at akka.dispatch.ExecutorServiceDelegate.execute$(ThreadPoolBuilder.scala:219)
    at akka.dispatch.Dispatcher$LazyExecutorServiceDelegate.execute(Dispatcher.scala:43)
    at akka.dispatch.Dispatcher.registerForExecution(Dispatcher.scala:127)
    at akka.dispatch.MessageDispatcher.attach(AbstractDispatcher.scala:152)
    at akka.actor.dungeon.Dispatch.start(Dispatch.scala:121)
[error] p.c.s.n.PlayRequestHandler - Cannot invoke the action
akka.stream.AbruptTerminationException: Processor actor [Actor[akka://application/system/Materializers/StreamSupervisor-0/flow-1-0-headSink#-440110538]] terminated abruptly

当前路由配置（conf/routes） #

GET     /robots.txt        controllers.Assets.at(path="/public", file="robots.txt")

解决建议 #

• 检查Kamon与Akka/Play版本兼容性：报错来自Kamon对Akka 2.6的Instrumentation代码空指针，大概率是版本不匹配，升级或降级Kamon到适配当前框架版本的稳定版。
• 临时禁用Kamon的Akka Dispatcher监控：在Kamon配置文件中添加kamon.instrumentation.akka.dispatchers.enabled = false，绕过有问题的监控逻辑。
• 排查Docker镜像依赖打包：确认构建镜像时所有依赖（包括Kamon相关）都完整打包，无版本冲突或缺失。
• 改用Play默认静态文件路由：Play框架默认会把public/目录下的文件映射到根路径，无需手动配置robots.txt的路由，直接删除自定义路由后重试访问。

内容的提问来源于stack exchange，提问作者Nandha