获取 Akka stream 代码错误“主”线程 java.lang.NoClassDefFoundError: scala/Function1$class

Question

I am getting below java error, when I am running the akka stream code: ** Exception in thread "main" java.lang.NoClassDefFoundError: scala/Function1$class at akka.stream.Supervision$$anon$1.(Supervision.scala:57) at akka.stream.Supervision$.(Supervision.scala:57) at akka.stream.Supervision$.(Supervision.scala) at akka.stream.ActorMaterializerSettings$.apply(ActorMaterializer.scala:268) at akka.stream.ActorMaterializerSettings$.apply(ActorMaterializer.scala:258) at ZBF0937 FCB05B460E447A0BEA7537218AZ.stream.ActorMaterializer$$anonfun$1.apply(ActorMaterializer.scala:42) at akka.stream.ActorMaterializer$$anonfun$1.apply(ActorMaterializer.scala:42) at scala.Option.getOrElse(Option.scala:121) at akka.stream.ActorMaterializer$.apply(ActorMaterializer.scala:42) at akka.stream.ActorMaterializer$.create(ActorMaterializer.scala:111) at akka.stream.ActorMaterializer.create(ActorMaterializer.scala) at com.accenture.akka.stream.Sample1.main(Sample1.Z93F 725A07423FE1C889F448B33D21F46Z:15) Caused by: java.lang.ClassNotFoundException: scala.Function1$class at java.net.URLClassLoader.findClass(URLClassLoader.java:381) at java.lang.ClassLoader.loadClass(ClassLoader.java:424) at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:349) at java.lang.ClassLoader.loadClass(ClassLoader.java:357)... 12 more ** Java Code:

import java.io.IOException;
import java.util.Arrays;

import akka.NotUsed;
import akka.actor.ActorSystem;
import akka.stream.ActorMaterializer;
import akka.stream.javadsl.Source;
public class Sample1 {
  public static void main(String[] args) throws IOException {
    final ActorSystem system = ActorSystem.create("Sys");
    final ActorMaterializer materializer = ActorMaterializer.create(system);

    final String text =
      "Lorem Ipsum is simply dummy text of the printing and typesetting industry. " +
      "Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, " +
      "when an unknown printer took a galley of type and scrambled it to make a type " +
      "specimen book.";

    Source.from(Arrays.asList(text.split("\\s"))).
      // transform
      map(e -> e.toUpperCase()).
      // print to console
      runForeach(System.out::println, materializer).
      handle((done, failure) -> {
        system.terminate();
        return NotUsed.getInstance();
      });
  }

}

Maven code:

<project xmlns="http://maven.apache.org/POM/4.0.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>com.accenture.akka</groupId>
    <artifactId>AkkaDemo</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <build>
        <sourceDirectory>src</sourceDirectory>
        <plugins>
            <plugin>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.8.0</version>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                </configuration>
            </plugin>
        </plugins>
    </build>
    <dependencies>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
            <scope>test</scope>
        </dependency>


        <!-- akka dependency -->
        <dependency>
            <groupId>com.typesafe.akka</groupId>
            <artifactId>akka-actor_2.12</artifactId>
            <version>2.5.11</version>
        </dependency>
        <dependency>
            <groupId>org.apache.kafka</groupId>
            <artifactId>kafka_2.11</artifactId>
            <version>1.1.0</version>
        </dependency>
        <dependency>
            <groupId>com.typesafe.akka</groupId>
            <artifactId>akka-stream_2.11</artifactId>
            <version>2.5.2</version>
        </dependency>
        <dependency>
            <groupId>com.typesafe.akka</groupId>
            <artifactId>akka-stream-testkit_2.11</artifactId>
            <version>2.5.2</version>
        </dependency>
        <dependency>
            <groupId>org.scala-lang</groupId>
            <artifactId>scala-library</artifactId>
            <version>2.12.0</version>
        </dependency>
    </dependencies>
</project>

Please tell us what I am doing wrong

Answer 1

Your dependencies mix libraries that have been compiled for different Scala versions. In general, Scala does not guarantee binary compatibility between minor versions, which is why the dependencies contain _2.11 or _2.12 in the artifact IDs. You need to choose one and use it consistently. In this case, since you are including scala-library version 2.12.0 , you should use artifacts ending with _2.12 . It's also important not to mix different versions of Akka libraries, so you should use 2.5.11 for all of the Akka dependencies. I would also recommend assigning the akka-stream-testkit dependency to the test scope, as with junit . Here's a corrected example:

    <dependency>
        <groupId>com.typesafe.akka</groupId>
        <artifactId>akka-actor_2.12</artifactId>
        <version>2.5.11</version>
    </dependency>
    <dependency>
        <groupId>org.apache.kafka</groupId>
        <artifactId>kafka_2.12</artifactId>
        <version>1.1.0</version>
    </dependency>
    <dependency>
        <groupId>com.typesafe.akka</groupId>
        <artifactId>akka-stream_2.12</artifactId>
        <version>2.5.11</version>
    </dependency>
    <dependency>
        <groupId>com.typesafe.akka</groupId>
        <artifactId>akka-stream-testkit_2.12</artifactId>
        <version>2.5.11</version>
        <scope>test</scope>
    </dependency>

Note that it is safe to update the patch version of scala-libary without changing other dependencies. Currently, the latest version of Scala 2.12 is 2.12.11. Using the latest version will ensure you have all of the bug fixes:

    <dependency>
        <groupId>org.scala-lang</groupId>
        <artifactId>scala-library</artifactId>
        <version>2.12.11</version>
    </dependency>

Similarly, the latest version of Akka 2.5 is 2.5.31. I would recommend you use that instead of 2.5.11.

I would also recommend defining akka.version and scala.binary.version as Maven properties , to allow you to easily change them in one place.

Putting all of the recommendations together:

<project xmlns="http://maven.apache.org/POM/4.0.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>com.accenture.akka</groupId>
    <artifactId>AkkaDemo</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <build>
        <sourceDirectory>src</sourceDirectory>
        <plugins>
            <plugin>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.8.0</version>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                </configuration>
            </plugin>
        </plugins>
    </build>
    <dependencies>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
            <scope>test</scope>
        </dependency>


        <!-- akka dependency -->
        <dependency>
            <groupId>com.typesafe.akka</groupId>
            <artifactId>akka-actor_${scala.binary.version}</artifactId>
            <version>${akka.version}</version>
        </dependency>
        <dependency>
            <groupId>org.apache.kafka</groupId>
            <artifactId>kafka_${scala.binary.version}</artifactId>
            <version>1.1.0</version>
        </dependency>
        <dependency>
            <groupId>com.typesafe.akka</groupId>
            <artifactId>akka-stream_${scala.binary.version}</artifactId>
            <version>${akka.version}</version>
        </dependency>
        <dependency>
            <groupId>com.typesafe.akka</groupId>
            <artifactId>akka-stream-testkit_${scala.binary.version}</artifactId>
            <version>${akka.version}</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.scala-lang</groupId>
            <artifactId>scala-library</artifactId>
            <version>2.12.11</version>
        </dependency>
    </dependencies>
    <properties>
        <akka.version>2.5.31</akka.version>
        <scala.binary.version>2.12</scala.binary.version>
    </properties>
</project>