继承和聚合UML(Inheritance and aggregation UML)

 一般来说回答你的问题：Akka创建了一个用于进行异步消息处理的线程池。 因此，如果你编写如下代码，你的应用程序永远不会终止，因为Akka继续运行。 
 
class Root extends Actor {

  // create some child actors to do some work

  override def receive: Receive = Actor.emptyBehavior
}

object Main {

  def main(args: Array[String]): Unit = {
    val system = ActorSystem("main")
    system.actorOf(Props(new Root))
  }
}
 
 因此，通常如果您需要终止应用程序，您将定义一条消息，表明已完成所有工作并将此消息发送给您的根执行者。 然后，根actor可以调用context.system.terminate()来终止系统。 
 
 回到你的问题，我不明白你为什么要把Akka和Spring Boot结合起来。 你的线程转储，我不确定问题是否与Akka有关。 看起来线程挂在HttpClient中。 您确定已释放并关闭所有打开的连接吗？ 

To answer your question generally: Akka creates a thread pool which is used to do asynchronous message processing. So if you write code like the following, your application would never terminate since Akka keeps on running.
 
class Root extends Actor {

  // create some child actors to do some work

  override def receive: Receive = Actor.emptyBehavior
}

object Main {

  def main(args: Array[String]): Unit = {
    val system = ActorSystem("main")
    system.actorOf(Props(new Root))
  }
}
 
So usually if you need to terminate your application you would define a message which signals that all work has been done and send this message to your root actor. The root actor can then call context.system.terminate() to terminate the system.
 
Coming back to your question, I don't understand why you would want to combine Akka with Spring Boot. Your thread dump, I'm not sure whether the problem is related to Akka at all. It looks like the threads are hanging inside HttpClient. Are you sure you have freed and closed all open connections?