Java Kafka Consumer noClassDefFoundError

Question

I am learning using a test Kafka consumer & producer however facing below error.

Kafka consumer program:

package kafka001;

import java.util.Arrays;
import java.util.Properties;
import java.util.Scanner;
import org.apache.kafka.clients.consumer.*;
import org.apache.kafka.common.errors.WakeupException;

public class ConsumerApp {
    private static Scanner in;
    private static boolean stop = false;

    public static void main(String[] args) throws Exception {
        System.out.println(args[0] + args.length);
        if (args.length != 2) {
            System.err.printf("Usage: %s <topicName> <groupId>\n");
            System.exit(-1);

        }

        in = new Scanner(System.in);
        String topicName = args[0];
        String groupId = args[1];
        ConsumerThread consumerRunnable = new ConsumerThread(topicName, groupId);
        consumerRunnable.start();
        //System.out.println("Here");   
        String line = "";
        while (!line.equals("exit")) {
            line = in.next();
        }
        consumerRunnable.getKafkaConsumer().wakeup();
        System.out.println("Stopping consumer now.....");
        consumerRunnable.join();

    }

    private static class ConsumerThread extends Thread{
        private String topicName;
        private String groupId;
        private KafkaConsumer<String,String> kafkaConsumer;
        public ConsumerThread(String topicName, String groupId){
            //System.out.println("inside ConsumerThread constructor");  
            this.topicName = topicName;
            this.groupId = groupId;
        }

        public void run() {
            //System.out.println("inside run"); 
            // Setup Kafka producer properties
            Properties configProperties = new Properties();
            configProperties.put(ConsumerConfig.BOOTSTRAP_SERVERS_CONFIG, "aup7727s.unix.anz:9092");
            configProperties.put(ConsumerConfig.KEY_DESERIALIZER_CLASS_CONFIG, "org.apache.kafka.common.serialization.StringDeserializer");
            configProperties.put(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG, "org.apache.kafka.common.serialization.StringDeserializer");
            configProperties.put(ConsumerConfig.GROUP_ID_CONFIG, groupId);
            configProperties.put(ConsumerConfig.CLIENT_ID_CONFIG, "simple");

            // subscribe to topic
            kafkaConsumer = new KafkaConsumer<String, String>(configProperties);
            kafkaConsumer.subscribe(Arrays.asList(topicName));

            // Get/process messages from topic and print it to console
            try {while(true) {
                ConsumerRecords<String, String> records = kafkaConsumer.poll(100);
                for (ConsumerRecord<String, String> record : records)
                    System.out.println(record.value());

            }
          } catch(WakeupException ex) {
              System.out.println("Exception caught " + ex.getMessage());
          }finally {
              kafkaConsumer.close();
              System.out.println("After closing KafkaConsumer");
          }

        }

        public KafkaConsumer<String,String> getKafkaConsumer(){
            return this.kafkaConsumer;
         }


    }
}

When I compile the code, I am noticing following class files:

ConsumerApp$ConsumerThread.class and ConsumerApp.class

I've generated jar file named ConsumerApp.jar through eclipse and when I run this in Hadoop cluster, I get noclassdeffound error as below:

java -cp ConsumerApp.jar kafka001/ConsumerApp console1 group1
or
hadoop jar ConsumerApp.jar console1 group1

Exception in thread "main" java.lang.NoClassDefFoundError: org.apache.kafka.common.errors.WakeupException
        at kafka001.ConsumerApp.main(ConsumerApp.java:24)
Caused by: java.lang.ClassNotFoundException: org.apache.kafka.common.errors.WakeupException
        at java.net.URLClassLoader.findClass(URLClassLoader.java:607)
        at java.lang.ClassLoader.loadClassHelper(ClassLoader.java:846)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:825)
        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:325)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:805)
        ... 1 more

I am using Eclipse to compile, maven build and generate jar file. Line number 24 correspond to creation of ConsumerThread instance.

I am unable to resolve if its due to ConsumerThread class name being incorrectly saved (Class file generated as ConsumerApp$ConsumerThread.class instead of ConsumerThread.class) ? or something to be taken care while generating jar file ?

Answer 1

Since I can't view the entire project, I would try this: Right click on the project -> go to Maven 2 tools -> click generate artifacts (check for updates). That should create any missing dependencies. Also make sure you check out other similar posts that may resolve your issue like this.