获取 Akka 流代码时出错 线程"main" java.lang.NoClassDefFoundError： scala/Function1$class

Question

当我运行 akka 流代码时，我遇到以下 java 错误： ** 线程"main"中的异常 java.lang.NoClassDefFoundError： scala/Function1$class 在akka.stream.Supervision$$anon$1。(监督：57( 在akka.stream.Supervision$。(监督：57( 在akka.stream.Supervision$。(监督斯卡拉( at akka.stream.ActorMaterializerSettings$.apply(ActorMaterializer.scala：268( at akka.stream.ActorMaterializerSettings$.apply(ActorMaterializer.scala：258( at akka.stream.ActorMaterializer$$anonfun$1.apply(ActorMaterializer.scala：42( at akka.stream.ActorMaterializer$$anonfun$1.apply(ActorMaterializer.scala：42( 在斯卡拉。Option.getOrElse(Option.scala：121( at akka.stream.ActorMaterializer$.apply(ActorMaterializer.scala：42( at akka.stream.ActorMaterializer$.create(ActorMaterializer.scala：111( at akka.stream.ActorMaterializer.create(ActorMaterializer.scala( at com.accenture.akka.stream.Sample1.main(Sample1.java：15( 原因：java.lang.ClassNotFoundException： scala.函数1$类 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 更多 ** 爪哇代码：

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。您需要选择一个并始终如一地使用它。在这种情况下，由于您要包含scala-library版本2.12.0，因此应使用以_2.12结尾的项目。不要混合不同版本的 Akka 库也很重要，因此您应该对所有 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。下面是一个更正的示例：

<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的修补程序版本是安全的。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。

我还建议将akka.version和scala.binary.version定义为Maven属性，以便您可以在一个地方轻松更改它们。

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>