Error getting Akka stream code Exception in thread "main" java.lang.NoClassDefFoundError: scala/Function1$class

Question

当我是 运行 akka 流代码时，我遇到了 java 以下错误： ** 线程 "main" java.lang.NoClassDefFoundError 中的异常：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$.create(ActorMaterializer.scala:111) 在 akka.stream.ActorMaterializer.create(ActorMaterializer.scala) 在 com.accenture.akka.stream.Sample1.main(Sample1.java:15) 由以下原因引起：java.lang.ClassNotFoundException：scala.Function1$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) ... 还有 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>

请告诉我们我做错了什么

Answer 1

您的依赖项混合了为不同 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。您需要选择一个并始终如一地使用它。在这种情况下，由于您包含 scala-library 版本 2.12.0，因此您应该使用以 _2.12 结尾的工件。不要混合不同版本的 Akka 库也很重要，因此您应该为所有 Akka 依赖项使用 2.5.11。我还建议将 akka-stream-testkit 依赖项分配给 test 范围，就像 junit 一样。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>

请注意，在不更改其他依赖项的情况下更新 scala-libary 的补丁版本是安全的。目前，Scala 2.12 的最新版本是 2.12.11。使用最新版本将确保您拥有所有错误修复：

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

同理，Akka 2.5最新版本为2.5.31。我建议您使用它而不是 2.5.11。

我还建议将 akka.version 和 scala.binary.version 定义为 Maven properties，以便您可以轻松地在一个地方更改它们。

将所有建议放在一起：

<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>