Question

所以我之前对如何在java maven项目中使用spark查询cassandra有一些疑问：Querying Data in Cassandra via Spark in a Java Maven Project

我的问题得到了解答并且有效，但是我遇到了一个问题（可能是一个问题）。我现在尝试使用datastax java API。这是我的代码：

package com.angel.testspark.test2;

import org.apache.commons.lang3.StringUtils;
import org.apache.spark.SparkConf;
import org.apache.spark.api.java.JavaRDD;
import org.apache.spark.api.java.JavaSparkContext;
import org.apache.spark.api.java.function.Function;

import java.io.Serializable;

import static com.datastax.spark.connector.CassandraJavaUtil.*;


public class App 
{

    // firstly, we define a bean class
    public static class Person implements Serializable {
        private Integer id;
        private String fname;
        private String lname;
        private String role;

        // Remember to declare no-args constructor
        public Person() { }

        public Integer getId() { return id; }
        public void setId(Integer id) { this.id = id; }

        public String getfname() { return fname; }
        public void setfname(String fname) { this.fname = fname; }

        public String getlname() { return lname; }
        public void setlname(String lname) { this.lname = lname; }

        public String getrole() { return role; }
        public void setrole(String role) { this.role = role; }

        // other methods, constructors, etc.
    }

    private transient SparkConf conf;
    private App(SparkConf conf) {
        this.conf = conf;
    }


    private void run() {
        JavaSparkContext sc = new JavaSparkContext(conf);
        createSchema(sc);


        sc.stop();
    }

    private void createSchema(JavaSparkContext sc) {

        JavaRDD<String> rdd = javaFunctions(sc).cassandraTable("tester", "empbyrole", Person.class)
                .where("role=?", "IT Engineer").map(new Function<Person, String>() {
                    @Override
                    public String call(Person person) throws Exception {
                        return person.toString();
                    }
                });
        System.out.println("Data as Person beans: \n" + StringUtils.join("\n", rdd.toArray()));
               }



    public static void main( String[] args )
    {
        if (args.length != 2) {
            System.err.println("Syntax: com.datastax.spark.demo.JavaDemo <Spark Master URL> <Cassandra contact point>");
            System.exit(1);
        }

        SparkConf conf = new SparkConf();
        conf.setAppName("Java API demo");
        conf.setMaster(args[0]);
        conf.set("spark.cassandra.connection.host", args[1]);

        App app = new App(conf);
        app.run();
    }
}

这是我的错误：

Exception in thread "main" org.apache.spark.SparkException: Job aborted: Task not serializable: java.io.NotSerializableException: com.angel.testspark.test2.App
    at org.apache.spark.scheduler.DAGScheduler$$anonfun$org$apache$spark$scheduler$DAGScheduler$$abortStage$1.apply(DAGScheduler.scala:1020)
    at org.apache.spark.scheduler.DAGScheduler$$anonfun$org$apache$spark$scheduler$DAGScheduler$$abortStage$1.apply(DAGScheduler.scala:1018)
    at scala.collection.mutable.ResizableArray$class.foreach(ResizableArray.scala:59)
    at scala.collection.mutable.ArrayBuffer.foreach(ArrayBuffer.scala:47)
    at org.apache.spark.scheduler.DAGScheduler.org$apache$spark$scheduler$DAGScheduler$$abortStage(DAGScheduler.scala:1018)
    at org.apache.spark.scheduler.DAGScheduler.org$apache$spark$scheduler$DAGScheduler$$submitMissingTasks(DAGScheduler.scala:781)
    at org.apache.spark.scheduler.DAGScheduler.org$apache$spark$scheduler$DAGScheduler$$submitStage(DAGScheduler.scala:724)
    at org.apache.spark.scheduler.DAGScheduler.processEvent(DAGScheduler.scala:554)
    at org.apache.spark.scheduler.DAGScheduler$$anonfun$start$1$$anon$2$$anonfun$receive$1.applyOrElse(DAGScheduler.scala:190)
    at akka.actor.ActorCell.receiveMessage(ActorCell.scala:498)
    at akka.actor.ActorCell.invoke(ActorCell.scala:456)
    at akka.dispatch.Mailbox.processMailbox(Mailbox.scala:237)
    at akka.dispatch.Mailbox.run(Mailbox.scala:219)
    at akka.dispatch.ForkJoinExecutorConfigurator$AkkaForkJoinTask.exec(AbstractDispatcher.scala:386)
    at scala.concurrent.forkjoin.ForkJoinTask.doExec(ForkJoinTask.java:260)
    at scala.concurrent.forkjoin.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1339)
    at scala.concurrent.forkjoin.ForkJoinPool.runWorker(ForkJoinPool.java:1979)
    at scala.concurrent.forkjoin.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:107)

现在我知道我的错误究竟在哪里。它是System.out.println("Data as Person beans: \n" + StringUtils.join("\n", rdd.toArray()));因为我需要将rdd转换为数组。但是，API文档SAID i应该能够执行此操作...这是从文档中复制和粘贴的代码。为什么我不能将RDD序列化为数组？

我已经使用上面链接中包含的帖子中的插入内容将伪数据插入到我的cassandra中。

此外，我解决的先前错误是当我将所有getter和setter更改为小写时。当我在其中使用大写字母时，它会产生错误。为什么我不能在我的吸气剂和制定者中使用大写字母？

谢谢，天使

Answer 1

将public class App更改为public class App implements Serializable可以解决错误。因为java内部类将保留对外部类的引用，所以Function对象将引用App。由于Spark需要序列化您的Function对象，因此App也需要序列化。

RDD不可序列化的Cassandra / Spark连接器java API

1 个答案: