org/apache/flink/streaming/api/scala/StreamExecutionEnvironment :java.lang.NoClassDefFoundError

Question

package com.knoldus
import org.apache.flink.api.java.utils.ParameterTool
import org.apache.flink.streaming.api.scala._
import org.apache.flink.streaming.api.windowing.time.Time

object SocketWindowWordCount {

  def main(args: Array[String]) : Unit = {

    var hostname: String = "localhost"
    var port: Int = 9000

    try {
     val params = ParameterTool.fromArgs(args)
      hostname = if (params.has("hostname")) params.get("hostname") else "localhost"
      port = params.getInt("port")
    } catch {
      case e: Exception => {
        System.err.println("No port specified. Please run 'SocketWindowWordCount " +
          "--hostname <hostname> --port <port>', where hostname (localhost by default) and port " +
          "is the address of the text server")
        System.err.println("To start a simple text server, run 'netcat -l <port>' " +
          "and type the input text into the command line")
        return
      }
    }

    // get the execution environment
    val env: StreamExecutionEnvironment = StreamExecutionEnvironment.getExecutionEnvironment

    // get input data by connecting to the socket
    val text: DataStream[String] = env.socketTextStream(hostname, port, '\n')

    // parse the data, group it, window it, and aggregate the counts
    val windowCounts = text
      .flatMap { w => w.split("\\s") }
      .map { w => WordWithCount(w, 1) }
      .keyBy("word")
      .timeWindow(Time.seconds(5))
      .sum("count")

    // print the results with a single thread, rather than in parallel
    windowCounts.print().setParallelism(1)

    env.execute("Socket Window WordCount")
  }

  /** Data type for words with count */

  case class WordWithCount(word: String, count: Long)

}

最后，当我在Intellij上运行这段代码时，我得到了这个错误

Exception in thread "main" java.lang.NoClassDefFoundError: org/apache/flink/streaming/api/scala/StreamExecutionEnvironment$
    at com.knoldus.SocketWindowWordCount$.main(SocketWindowWordCount.scala:43)
    at com.knoldus.SocketWindowWordCount.main(SocketWindowWordCount.scala)
Caused by: java.lang.ClassNotFoundException: org.apache.flink.streaming.api.scala.StreamExecutionEnvironment$
    at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:581)
    at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:178)
    at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:521)
    ... 2 more

Answer 1

我通过删除maven导入中存在的<scope>provided</scope>解决了这个问题。