在线程“ main”中获取Akka流代码时出错，异常java.lang.NoClassDefFoundError：scala / Function1 $ class

Question

当我运行akka流代码时，我遇到了Java错误：**线程“主”中的异常java.lang.NoClassDefFoundError：scala / Function1 $ class在akka.stream.Supervision $$ anon $ 1。（Supervision.scala：57）在akka.stream.Supervision $。（Supervision.scala：57）在akka.stream.Supervision $。（Supervision.scala）在akka.stream.ActorMaterializerSettings $ .apply（ActorMaterializer.scala：268）在akka.stream.ActorMaterializerSettings $ .apply（ActorMaterializer.scala：258）在akka.stream.ActorMaterializer $$ anonfun $ 1.apply（ActorMaterializer.scala：42）在akka.stream.ActorMaterializer $$ anonfun $ 1.apply（ActorMaterializer.scala：42）在scala.Option.getOrElse（Option.scala：121）在akka.stream.ActorMaterializer $ .apply（ActorMaterializer.scala：42）在akka.stream.ActorMaterializer $ .create（ActorMaterializer.scala：111）在akka.stream.ActorMaterializer.create（ActorMaterializer.scala）在com.accenture.akka.stream.Sample1.main（Sample1.java:15）引起原因：java.lang.ClassNotFoundException：scala.Function1 $ class在java.net.URLClassLoader.findClass（URLClassLoader.java:381）在java.lang.ClassLoader.loadClass（ClassLoader.java:424）在sun.misc.Launcher $ AppClassLoader.loadClass（Launcher.java:349）在java.lang.ClassLoader.loadClass（ClassLoader.java:357）...另外12个**Java代码：

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代码：

<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>

请告诉我们我在做什么错

Answer 1

您的依赖项混合了为不同的Scala版本编译的库。通常，Scala不保证次要版本之间的二进制兼容性，这就是为什么依赖项在工件ID中包含_2.11或_2.12的原因。您需要选择一个并持续使用它。在这种情况下，由于要包括scala-library版本2.12.0，因此应使用以_2.12结尾的工件。同样重要的是不要混合使用不同版本的Akka库，因此对于所有Akka依赖项都应使用2.5.11。我也建议像akka-stream-testkit一样，将test依赖项分配给junit范围。这是一个更正的示例：

    <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>

注意，可以安全地更新scala-libary的补丁程序版本，而无需更改其他依赖项。当前，Scala 2.12的最新版本是2.12.11。使用最新版本将确保您具有所有错误修复：

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

同样，Akka 2.5的最新版本是2.5.31。我建议您使用它而不是2.5.11。

[我也建议将akka.version和scala.binary.version定义为Maven properties，以便您可以轻松地在一个地方进行更改。

将所有建议汇总在一起：

<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>