尝试在命令行上运行Java Spark应用程序时的NoClassDefFoundError

java -cp /path/to/spark/jars/*:/path/to/your/application.jar com.yourcompany.YourMainClass

<build>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-dependency-plugin</artifactId>
            <version>3.1.2</version>
            <executions>
                <execution>
                    <id>copy-dependencies</id>
                    <phase>package</phase>
                    <goals>
                        <goal>copy-dependencies</goal>
                    </goals>
                    <configuration>
                        <outputDirectory>${project.build.directory}/dependencies</outputDirectory>
                    </configuration>
                </version>
            </executions>
        </plugin>
    </plugins>
</build>

java -cp /path/to/your/application.jar:/path/to/dependencies/* com.yourcompany.YourMainClass

<build>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-assembly-plugin</artifactId>
            <version>3.3.0</version>
            <configuration>
                <descriptorRefs>
                    <descriptorRef>jar-with-dependencies</descriptorRef>
                </descriptorRefs>
                <archive>
                    <manifest>
                        <mainClass>com.yourcompany.YourMainClass</mainClass>
                    </manifest>
                </archive>
            </configuration>
            <executions>
                <execution>
                    <id>make-assembly</id>
                    <phase>package</phase>
                    <goals>
                        <goal>single</goal>
                    </goals>
                </execution>
            </executions>
        </plugin>
    </plugins>
</build>

java -jar /path/to/your/application-jar-with-dependencies.jar

package com.example;

import org.apache.spark.api.java.JavaSparkContext;
import org.apache.spark.api.java.JavaRDD;
import org.apache.spark.SparkConf;

public class WordCount {
    public static void main(String[] args) {
        SparkConf conf = new SparkConf().setAppName("wordCount").setMaster("local");
        JavaSparkContext sc = new JavaSparkContext(conf);

        JavaRDD<String> lines = sc.textFile("data.txt");
        JavaRDD<String> words = lines.flatMap(line -> Arrays.asList(line.split(" ")).iterator());
        JavaRDD<Integer> wordCounts = words.mapToPair(word -> new Tuple2<>(word, 1)).reduceByKey((a, b) -> a + b);

        wordCounts.saveAsTextFile("output");

        sc.stop();
    }
}

<dependencies>
    <dependency>
        <groupId>org.apache.spark</groupId>
        <artifactId>spark-core_2.12</artifactId>
        <version>3.1.2</version>
    </dependency>
</dependencies>