如何修复java.lang.ClassCastException：无法将scala.collection.immutable.List的实例分配给字段类型scala.collection.Seq？ [英] How to fix java.lang.ClassCastException: cannot assign instance of scala.collection.immutable.List to field type scala.collection.Seq?

问题描述

此错误一直是最难追踪的。我不知道发生了什么事。我在我的位置机器上运行Spark集群。所以整个火花集群在一个主机下面， 127.0.0.1 ，我在一个独立模式下运行

This error has been the hardest to trace. I am not sure what is going on. I am running a Spark cluster on my location machine. so the entire spark cluster is under one host which is 127.0.0.1 and I run on a standalone mode

JavaPairRDD<byte[], Iterable<CassandraRow>> cassandraRowsRDD= javaFunctions(sc).cassandraTable("test", "hello" )
   .select("rowkey", "col1", "col2", "col3",  )
   .spanBy(new Function<CassandraRow, byte[]>() {
        @Override
        public byte[] call(CassandraRow v1) {
            return v1.getBytes("rowkey").array();
        }
    }, byte[].class);

Iterable<Tuple2<byte[], Iterable<CassandraRow>>> listOftuples = cassandraRowsRDD.collect(); //ERROR HAPPENS HERE
Tuple2<byte[], Iterable<CassandraRow>> tuple = listOftuples.iterator().next();
byte[] partitionKey = tuple._1();
for(CassandraRow cassandraRow: tuple._2()) {
    System.out.println("************START************");
    System.out.println(new String(partitionKey));
    System.out.println("************END************");
}

此错误一直是最难追踪的。它显然发生在 cassandraRowsRDD.collect（），我不知道为什么？

This error has been the hardest to trace. It clearly happens at cassandraRowsRDD.collect() and I dont know why?

16/10/09 23:36:21 ERROR Executor: Exception in task 2.3 in stage 0.0 (TID 21)
java.lang.ClassCastException: cannot assign instance of scala.collection.immutable.List$SerializationProxy to field org.apache.spark.rdd.RDD.org$apache$spark$rdd$RDD$$dependencies_ of type scala.collection.Seq in instance of org.apache.spark.rdd.MapPartitionsRDD
    at java.io.ObjectStreamClass$FieldReflector.setObjFieldValues(ObjectStreamClass.java:2133)
    at java.io.ObjectStreamClass.setObjFieldValues(ObjectStreamClass.java:1305)
    at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:2006)
    at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1924)
    at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1801)
    at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1351)
    at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:2000)
    at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1924)
    at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1801)
    at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1351)
    at java.io.ObjectInputStream.readObject(ObjectInputStream.java:371)
    at org.apache.spark.serializer.JavaDeserializationStream.readObject(JavaSerializer.scala:75)
    at org.apache.spark.serializer.JavaSerializerInstance.deserialize(JavaSerializer.scala:114)
    at org.apache.spark.scheduler.ResultTask.runTask(ResultTask.scala:66)
    at org.apache.spark.scheduler.Task.run(Task.scala:85)
    at org.apache.spark.executor.Executor$TaskRunner.run(Executor.scala:274)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at java.lang.Thread.run(Thread.java:745)

以下是我使用的版本

Scala code runner version 2.11.8  // when I run scala -version or even ./spark-shell


compile group: 'org.apache.spark' name: 'spark-core_2.11' version: '2.0.0'
compile group: 'org.apache.spark' name: 'spark-streaming_2.11' version: '2.0.0'
compile group: 'org.apache.spark' name: 'spark-sql_2.11' version: '2.0.0'
compile group: 'com.datastax.spark' name: 'spark-cassandra-connector_2.11' version: '2.0.0-M3': 

我的gradle文件在引入一些名为提供的内容后看起来像这样，实际上似乎并不存在，但谷歌说要创建一个，所以我的build.gradle看起来像这样

my gradle file looks like this after introducing something called "provided" which actually doesn't seem to exist but google said to create one so my build.gradle looks like this

group 'com.company'
version '1.0-SNAPSHOT'

apply plugin: 'java'
apply plugin: 'idea'

repositories {
    mavenCentral()
    mavenLocal()
}

configurations {
    provided
}
sourceSets {
    main {
        compileClasspath += configurations.provided
        test.compileClasspath += configurations.provided
        test.runtimeClasspath += configurations.provided
    }
}

idea {
    module {
        scopes.PROVIDED.plus += [ configurations.provided ]
    }
}

dependencies {
    compile 'org.slf4j:slf4j-log4j12:1.7.12'
    provided group: 'org.apache.spark', name: 'spark-core_2.11', version: '2.0.0'
    provided group: 'org.apache.spark', name: 'spark-streaming_2.11', version: '2.0.0'
    provided group: 'org.apache.spark', name: 'spark-sql_2.11', version: '2.0.0'
    provided group: 'com.datastax.spark', name: 'spark-cassandra-connector_2.11', version: '2.0.0-M3'
}



jar {
    from { configurations.provided.collect { it.isDirectory() ? it : zipTree(it) } }
   // with jar
    from sourceSets.test.output
    manifest {
        attributes 'Main-Class': "com.company.batchprocessing.Hello"
    }
    exclude 'META-INF/.RSA', 'META-INF/.SF', 'META-INF/*.DSA'
    zip64 true
}

推荐答案

我遇到了同样的问题，可以通过添加来解决我的应用程序的jar用于激活类路径

I had the same issue and could resolve it by adding my application's jar to spark's classpath with

spark = SparkSession.builder()
        .appName("Foo")
        .config("spark.jars", "target/scala-2.11/foo_2.11-0.1.jar")

这篇关于如何修复java.lang.ClassCastException：无法将scala.collection.immutable.List的实例分配给字段类型scala.collection.Seq？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！