我安装了spark-2.4.4-bin-hadoop2.7，我想运行一些用Java编写的示例。为此，我使用了Intellij，创建了一个maven项目，并在程序包src -> main -> java中创建了Java类，并在其中复制了示例文件夹JavaSparkPi中的代码。
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import org.apache.spark.api.java.JavaRDD;
import org.apache.spark.api.java.JavaSparkContext;
import org.apache.spark.sql.SparkSession;
import java.util.ArrayList;
import java.util.List;
/**
* Computes an approximation to pi
* Usage: JavaSparkPi [partitions]
*/
public final class JavaSparkPi {
public static void main(String[] args) throws Exception {
SparkSession spark = SparkSession
.builder()
.appName("JavaSparkPi")
.getOrCreate();
JavaSparkContext jsc = new JavaSparkContext(spark.sparkContext());
int slices = (args.length == 1) ? Integer.parseInt(args[0]) : 2;
int n = 100000 * slices;
List<Integer> l = new ArrayList<>(n);
for (int i = 0; i < n; i++) {
l.add(i);
}
JavaRDD<Integer> dataSet = jsc.parallelize(l, slices);
int count = dataSet.map(integer -> {
double x = Math.random() * 2 - 1;
double y = Math.random() * 2 - 1;
return (x * x + y * y <= 1) ? 1 : 0;
}).reduce((integer, integer2) -> integer + integer2);
System.out.println("Pi is roughly " + 4.0 * count / n);
spark.stop();
}
}
在pom.xml中，我添加了以下依赖项：
<?xml version="1.0" encoding="UTF-8"?>
<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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>demo3</groupId>
<artifactId>demo3</artifactId>
<version>1.0-SNAPSHOT</version>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<configuration>
<source>8</source>
<target>8</target>
</configuration>
</plugin>
</plugins>
</build>
<dependencies>
<!-- https://mvnrepository.com/artifact/org.apache.spark/spark-sql -->
<dependency>
<groupId>org.apache.spark</groupId>
<artifactId>spark-sql_2.12</artifactId>
<version>2.4.4</version>
</dependency>
<!-- https://mvnrepository.com/artifact/org.apache.spark/spark-core -->
<dependency>
<groupId>org.apache.spark</groupId>
<artifactId>spark-core_2.12</artifactId>
<version>2.4.4</version>
</dependency>
</dependencies>
</project>
我构建了项目，但是当我尝试运行它时，出现以下错误：
Exception in thread "main" java.lang.NoSuchMethodError: scala.Product.$init$(Lscala/Product;)V
at org.apache.spark.SparkConf$DeprecatedConfig.<init>(SparkConf.scala:810)
at org.apache.spark.SparkConf$.<init>(SparkConf.scala:644)
at org.apache.spark.SparkConf$.<clinit>(SparkConf.scala)
at org.apache.spark.SparkConf.set(SparkConf.scala:95)
at org.apache.spark.SparkConf.set(SparkConf.scala:84)
at org.apache.spark.sql.SparkSession$Builder.$anonfun$getOrCreate$6(SparkSession.scala:928)
at scala.collection.mutable.HashMap$$anonfun$foreach$1.apply(HashMap.scala:130)
at scala.collection.mutable.HashMap$$anonfun$foreach$1.apply(HashMap.scala:130)
at scala.collection.mutable.HashTable$class.foreachEntry(HashTable.scala:236)
at scala.collection.mutable.HashMap.foreachEntry(HashMap.scala:40)
at scala.collection.mutable.HashMap.foreach(HashMap.scala:130)
at org.apache.spark.sql.SparkSession$Builder.$anonfun$getOrCreate$5(SparkSession.scala:928)
at scala.Option.getOrElse(Option.scala:121)
at org.apache.spark.sql.SparkSession$Builder.getOrCreate(SparkSession.scala:926)
at JavaSparkPi.main(JavaSparkPi.java:36)
为澄清起见，在第36行的.getOrCreate()中有一个SparkSession。
-------更新------- 现在我得到了这个错误：
19/11/18 13:23:40 ERROR SparkContext: Error initializing SparkContext.
org.apache.spark.SparkException: A master URL must be set in your configuration
at org.apache.spark.SparkContext.<init>(SparkContext.scala:368)
at org.apache.spark.SparkContext$.getOrCreate(SparkContext.scala:2520)
at org.apache.spark.sql.SparkSession$Builder.$anonfun$getOrCreate$5(SparkSession.scala:935)
at scala.Option.getOrElse(Option.scala:138)
at org.apache.spark.sql.SparkSession$Builder.getOrCreate(SparkSession.scala:926)
at JavaSparkPi.main(JavaSparkPi.java:36)
19/11/18 13:23:40 ERROR Utils: Uncaught exception in thread main
java.lang.NullPointerException
at org.apache.spark.SparkContext.postApplicationEnd(SparkContext.scala:2416)
at org.apache.spark.SparkContext.$anonfun$stop$2(SparkContext.scala:1931)
at org.apache.spark.util.Utils$.tryLogNonFatalError(Utils.scala:1340)
at org.apache.spark.SparkContext.stop(SparkContext.scala:1931)
at org.apache.spark.SparkContext.<init>(SparkContext.scala:585)
at org.apache.spark.SparkContext$.getOrCreate(SparkContext.scala:2520)
at org.apache.spark.sql.SparkSession$Builder.$anonfun$getOrCreate$5(SparkSession.scala:935)
at scala.Option.getOrElse(Option.scala:138)
at org.apache.spark.sql.SparkSession$Builder.getOrCreate(SparkSession.scala:926)
at JavaSparkPi.main(JavaSparkPi.java:36)
19/11/18 13:23:40 INFO SparkContext: Successfully stopped SparkContext
Exception in thread "main" org.apache.spark.SparkException: A master URL must be set in your configuration
at org.apache.spark.SparkContext.<init>(SparkContext.scala:368)
at org.apache.spark.SparkContext$.getOrCreate(SparkContext.scala:2520)
at org.apache.spark.sql.SparkSession$Builder.$anonfun$getOrCreate$5(SparkSession.scala:935)
at scala.Option.getOrElse(Option.scala:138)
at org.apache.spark.sql.SparkSession$Builder.getOrCreate(SparkSession.scala:926)
at JavaSparkPi.main(JavaSparkPi.java:36)