我正在使用 fs2-kafka阅读 embedded-kafka .
我使用 withRunningKafkaOnFoundPort 创建嵌入式 kafka，创建主题并发布一些消息。然而，当我尝试用 fs2-kafka 读回它时，我得到一个 NullPointerException。我已经隔离了一个测试用例，代码如下。
这是我的代码:
import cats.effect._
import cats.implicits._
import cats.effect.implicits._
import fs2.Stream
import fs2.kafka.{AutoOffsetReset, ConsumerSettings, KafkaConsumer, consumerStream}
import net.manub.embeddedkafka.{EmbeddedKafka, EmbeddedKafkaConfig}
import org.scalatest.{BeforeAndAfterAll, FunSuite}
import scala.concurrent.ExecutionContext
class KafkaSuite extends FunSuite with EmbeddedKafka {
val singleThreadExecutor = ExecutionContext.fromExecutor((task: Runnable) => task.run())
implicit val contextShift = IO.contextShift(singleThreadExecutor)
implicit val timer = IO.timer(singleThreadExecutor)
val topic = "example"
val partition = 0
val clientId = "client"
test("works") {
val userDefinedConfig = EmbeddedKafkaConfig(kafkaPort = 0, zooKeeperPort = 0)
withRunningKafkaOnFoundPort(userDefinedConfig) { implicit actualConfig =>
createCustomTopic(topic)
publishStringMessageToKafka(topic, "example-message1")
publishStringMessageToKafka(topic, "example-message2")
publishStringMessageToKafka(topic, "example-message3")
publishStringMessageToKafka(topic, "example-message4")
val broker = s"localhost:${actualConfig.kafkaPort}"
val consumerSettings = ConsumerSettings[IO, String, String]
.withAutoOffsetReset(AutoOffsetReset.Earliest)
.withBootstrapServers(broker)
.withGroupId("group")
.withClientId(clientId)
val r = consumerStream[IO].using(consumerSettings)
.evalTap(_.subscribeTo(topic))
.evalTap(_.seekToBeginning)
.flatMap { consumer =>
consumer.stream.take(1)
}
.compile
.toList
val res = r.unsafeRunSync()
Console.println(res)
assert(res.size == 1)
}
}
}
build.sbt:
name := "test"
version := "0.1"
scalaVersion := "2.12.6"
libraryDependencies ++= Seq(
"org.scalatest" % "scalatest_2.12" % "3.1.2" % "test",
"org.slf4j" % "slf4j-simple" % "1.7.25",
"com.github.fd4s" %% "fs2-kafka" % "1.0.0",
"io.github.embeddedkafka" %% "embedded-kafka" % "2.4.1.1" % Test
)
这是堆栈跟踪:
java.lang.NullPointerException was thrown.
java.lang.NullPointerException
at java.lang.String.<init>(String.java:515)
at fs2.kafka.Deserializer$.$anonfun$string$1(Deserializer.scala:208)
at fs2.kafka.Deserializer$.$anonfun$lift$1(Deserializer.scala:184)
at fs2.kafka.Deserializer$$anon$1.deserialize(Deserializer.scala:133)
at fs2.kafka.ConsumerRecord$.deserializeFromBytes(ConsumerRecord.scala:166)
at fs2.kafka.ConsumerRecord$.fromJava(ConsumerRecord.scala:177)
at fs2.kafka.internal.KafkaConsumerActor.$anonfun$records$2(KafkaConsumerActor.scala:378)
at cats.data.NonEmptyVectorInstances$$anon$1.traverse(NonEmptyVector.scala:300)
at cats.data.NonEmptyVectorInstances$$anon$1.traverse(NonEmptyVector.scala:245)
at cats.Traverse$Ops.traverse(Traverse.scala:19)
at cats.Traverse$Ops.traverse$(Traverse.scala:19)
at cats.Traverse$ToTraverseOps$$anon$2.traverse(Traverse.scala:19)
at fs2.kafka.internal.KafkaConsumerActor.$anonfun$records$1(KafkaConsumerActor.scala:376)
at cats.instances.VectorInstances$$anon$1.$anonfun$traverse$2(vector.scala:80)
at cats.instances.VectorInstances$$anon$1.loop$2(vector.scala:43)
at cats.instances.VectorInstances$$anon$1.$anonfun$foldRight$2(vector.scala:44)
at cats.Eval$.advance(Eval.scala:271)
at cats.Eval$.loop$1(Eval.scala:350)
at cats.Eval$.cats$Eval$$evaluate(Eval.scala:368)
at cats.Eval$Defer.value(Eval.scala:257)
at cats.instances.VectorInstances$$anon$1.traverse(vector.scala:79)
at cats.instances.VectorInstances$$anon$1.traverse(vector.scala:15)
at cats.Traverse$Ops.traverse(Traverse.scala:19)
at cats.Traverse$Ops.traverse$(Traverse.scala:19)
at cats.Traverse$ToTraverseOps$$anon$2.traverse(Traverse.scala:19)
at fs2.kafka.internal.KafkaConsumerActor.records(KafkaConsumerActor.scala:373)
at fs2.kafka.internal.KafkaConsumerActor.$anonfun$poll$2(KafkaConsumerActor.scala:405)
at cats.effect.internals.IORunLoop$.liftedTree1$1(IORunLoop.scala:95)
at cats.effect.internals.IORunLoop$.cats$effect$internals$IORunLoop$$loop(IORunLoop.scala:95)
at cats.effect.internals.IORunLoop$.startCancelable(IORunLoop.scala:41)
at cats.effect.internals.IOBracket$BracketStart.run(IOBracket.scala:86)
at cats.effect.internals.Trampoline.cats$effect$internals$Trampoline$$immediateLoop(Trampoline.scala:70)
at cats.effect.internals.Trampoline.startLoop(Trampoline.scala:36)
at cats.effect.internals.TrampolineEC$JVMTrampoline.super$startLoop(TrampolineEC.scala:93)
at cats.effect.internals.TrampolineEC$JVMTrampoline.$anonfun$startLoop$1(TrampolineEC.scala:93)
at scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:12)
at scala.concurrent.BlockContext$.withBlockContext(BlockContext.scala:81)
at cats.effect.internals.TrampolineEC$JVMTrampoline.startLoop(TrampolineEC.scala:93)
at cats.effect.internals.Trampoline.execute(Trampoline.scala:43)
at cats.effect.internals.TrampolineEC.execute(TrampolineEC.scala:44)
at cats.effect.internals.IOBracket$BracketStart.apply(IOBracket.scala:72)
at cats.effect.internals.IOBracket$BracketStart.apply(IOBracket.scala:52)
at cats.effect.internals.IORunLoop$.cats$effect$internals$IORunLoop$$loop(IORunLoop.scala:136)
at cats.effect.internals.IORunLoop$RestartCallback.signal(IORunLoop.scala:355)
at cats.effect.internals.IORunLoop$RestartCallback.apply(IORunLoop.scala:376)
at cats.effect.internals.IORunLoop$RestartCallback.apply(IORunLoop.scala:316)
at cats.effect.internals.IOShift$Tick.run(IOShift.scala:36)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
最佳答案
原来问题是 ConsumerSettings[IO, String, String] 中的键类型是 String 但 embedded-kafka 写入 Null作为 key ，因此在反序列化 key 时它会因 NullPointerException 而失败。将键类型设置为 Unit 解决了异常问题。
另一个问题是 withRunningKafkaOnFoundPort 在 IO 评估开始之前完成。要让它运行，需要从 embedded-kafka 创建一个 Resource 并将 IO 包装到其中。
val embeddedKafka = Resource.make(IO(EmbeddedKafka.start()))((kafka) => IO(kafka.stop(true)))
下一个问题是 fs2-kafka 无法与单线程执行器一起工作，因此您必须为其提供一个执行器池(例如 ExecutionContext.global)。
这是一个完整的工作示例:
import cats.effect._
import fs2.Stream
import fs2.kafka.{AutoOffsetReset, ConsumerSettings, consumerStream}
import net.manub.embeddedkafka.{EmbeddedKafka, EmbeddedKafkaConfig}
import org.scalatest.FunSuite
import scala.concurrent.ExecutionContext
class KafkaSuite extends FunSuite with EmbeddedKafka {
implicit val ec = ExecutionContext.global
implicit val contextShift = IO.contextShift(ec)
implicit val timer = IO.timer(ec)
val topic = "example"
val partition = 0
val clientId = "client"
val userDefinedConfig = EmbeddedKafkaConfig(kafkaPort = 0, zooKeeperPort = 0)
def broker(port: Long) = s"localhost:${port}"
val consumerSettings = ConsumerSettings[IO, Unit, String]
.withAutoOffsetReset(AutoOffsetReset.Earliest)
.withEnableAutoCommit(true)
.withGroupId("group")
.withClientId(clientId)
val embeddedKafka = Resource.make(IO(EmbeddedKafka.start()))((kafka) => IO(kafka.stop(true)))
test("works") {
val r = Stream.resource(embeddedKafka).flatMap { kafka =>
implicit val actualConfig: EmbeddedKafkaConfig = kafka.config
createCustomTopic(topic)
publishStringMessageToKafka(topic, "example-message1")
publishStringMessageToKafka(topic, "example-message2")
publishStringMessageToKafka(topic, "example-message3")
publishStringMessageToKafka(topic, "example-message4")
consumerStream(consumerSettings.withBootstrapServers(broker(actualConfig.kafkaPort)))
.evalTap(_.subscribeTo(topic))
.evalTap(_.seekToBeginning)
.flatMap(_.stream)
.map(_.record.value)
.take(1)
}
val res = r.compile.toList.unsafeRunSync()
assert(res.contains("example-message1"))
}
}
关于scala - 如何使用 fs2-kafka 从 embedded-kafka 读取数据，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/62598197/