Lagom Server: java.lang.IllegalArgumentException

Question

I am creating a module in lagom project. My module have only kafka consumer for consuming messages and store message events in cassandra. Thanks why, in my LagomApplicationLoader I am not defining any service and initialize lagomServer empty with LagomServer.forServices(). But whenever, I am start my application, I am getting following exception:

java.lang.IllegalArgumentException
    at com.lightbend.lagom.scaladsl.server.LagomServer$$anon$2.<init>(LagomServer.scala:35)
    at com.lightbend.lagom.scaladsl.server.LagomServer$.forServices(LagomServer.scala:31)
    at com.knoldus.consumer.impl.TwitterConsumerApplication.lagomServer$lzycompute(TwitterConsumerLoader.scala:33)
    at com.knoldus.consumer.impl.TwitterConsumerApplication.lagomServer(TwitterConsumerLoader.scala:33)
    at com.lightbend.lagom.scaladsl.server.LagomApplication.<init>(LagomApplicationLoader.scala:187)
    at com.knoldus.consumer.impl.TwitterConsumerApplication.<init>(TwitterConsumerLoader.scala:28)
    at com.knoldus.consumer.impl.TwitterConsumerLoader$$anon$1.<init>(TwitterConsumerLoader.scala:25)
    at com.knoldus.consumer.impl.TwitterConsumerLoader.loadDevMode(TwitterConsumerLoader.scala:25)
    at com.lightbend.lagom.scaladsl.server.LagomApplicationLoader.load(LagomApplicationLoader.scala:54)
    at play.core.server.LagomReloadableDevServerStart$$anonfun$mainDev$1$$anon$2$$anonfun$get$1$$anonfun$apply$1$$anonfun$2$$anonfun$3.apply(LagomReloadableDevServerStart.scala:151)
    at play.core.server.LagomReloadableDevServerStart$$anonfun$mainDev$1$$anon$2$$anonfun$get$1$$anonfun$apply$1$$anonfun$2$$anonfun$3.apply(LagomReloadableDevServerStart.scala:148)
    at play.utils.Threads$.withContextClassLoader(Threads.scala:21)
    at play.core.server.LagomReloadableDevServerStart$$anonfun$mainDev$1$$anon$2$$anonfun$get$1$$anonfun$apply$1$$anonfun$2.apply(LagomReloadableDevServerStart.scala:148)
    at play.core.server.LagomReloadableDevServerStart$$anonfun$mainDev$1$$anon$2$$anonfun$get$1$$anonfun$apply$1$$anonfun$2.apply(LagomReloadableDevServerStart.scala:124)
    at scala.Option.map(Option.scala:146)
    at play.core.server.LagomReloadableDevServerStart$$anonfun$mainDev$1$$anon$2$$anonfun$get$1$$anonfun$apply$1.apply(LagomReloadableDevServerStart.scala:124)
    at play.core.server.LagomReloadableDevServerStart$$anonfun$mainDev$1$$anon$2$$anonfun$get$1$$anonfun$apply$1.apply(LagomReloadableDevServerStart.scala:122)
    at scala.util.Success.flatMap(Try.scala:231)
    at play.core.server.LagomReloadableDevServerStart$$anonfun$mainDev$1$$anon$2$$anonfun$get$1.apply(LagomReloadableDevServerStart.scala:122)
    at play.core.server.LagomReloadableDevServerStart$$anonfun$mainDev$1$$anon$2$$anonfun$get$1.apply(LagomReloadableDevServerStart.scala:114)
    at scala.concurrent.impl.Future$PromiseCompletingRunnable.liftedTree1$1(Future.scala:24)
    at scala.concurrent.impl.Future$PromiseCompletingRunnable.run(Future.scala:24)
    at java.util.concurrent.ForkJoinTask$RunnableExecuteAction.exec(ForkJoinTask.java:1402)
    at java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:289)
    at java.util.concurrent.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1056)
    at java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1692)
    at java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:157)

My Code:

class TwitterConsumerLoader extends LagomApplicationLoader {

  override def load(context: LagomApplicationContext): LagomApplication =
    new TwitterConsumerApplication(context) {
      override def serviceLocator = NoServiceLocator
    }

  override def loadDevMode(context: LagomApplicationContext): LagomApplication =
    new TwitterConsumerApplication(context) with LagomDevModeComponents
}

abstract class TwitterConsumerApplication(context: LagomApplicationContext) extends LagomApplication(context)
  with CassandraPersistenceComponents with AhcWSComponents with LagomKafkaComponents {

  lazy val twitterService = serviceClient.implement[TwitterProducerService]

  override lazy val lagomServer = LagomServer.forServices()
  override lazy val jsonSerializerRegistry = TwitterSerializerRegistry

  persistentEntityRegistry.register(wire[TweetEntity])
  wire[TwitterProducerSubscriber]
}

How can I declare empty services in lagom. If this is not possible, what are the other alternatives? Because may be in future, it may required, for creating some service in this module. How can i resolve this issue?

score 0 · Answer 1 · answered Feb 27 '17 at 23:44

When you don't have any services to bind, you should instead declare a ServiceInfo.

In addition, for a service that only consumes from Kafka and does not publish topics of it's own, it's only necessary to mix in LagomKafkaClientComponents instead of LagomKafkaComponents. LagomKafkaClientComponents does not require a LagomServer, only a ServiceInfo.

You can declare ServiceInfo for a simple consumer that does not include any services like this:

override lazy val serviceInfo = ServiceInfo(clientName, Map.empty)

Where clientName is a unique, identifying string for this project that is used to name the Kafka client ID and default consumer group ID. You might use "twitterConsumer" in this example.

http://www.lagomframework.com/documentation/1.3.x/scala/ServiceInfo.html has more information on ServiceInfo.

Lagom Server: java.lang.IllegalArgumentException

1 Answers1