org.apache.kafka.common.KafkaException: io.confluent.kafka.serializers.KafkaAvroSerializer

Question

Try to construct a kafka consumer with following code

import org.apache.kafka.clients.consumer.ConsumerConfig;
import org.apache.kafka.clients.consumer.ConsumerRecord;
import org.apache.kafka.clients.consumer.ConsumerRecords;
import org.apache.kafka.clients.consumer.KafkaConsumer;
import org.apache.kafka.clients.producer.KafkaProducer;
import org.apache.kafka.clients.producer.ProducerConfig;
import org.apache.kafka.clients.producer.ProducerRecord;
// set up consumer
final Properties consumerProps = new Properties();
consumerProps.put(ConsumerConfig.BOOTSTRAP_SERVERS_CONFIG, CLUSTER.bootstrapServers());
consumerProps.put(ConsumerConfig.GROUP_ID_CONFIG, "consumer-tutorial");
consumerProps.put(ConsumerConfig.KEY_DESERIALIZER_CLASS_CONFIG,
        io.confluent.kafka.serializers.KafkaAvroSerializer.class);
consumerProps.put(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG,
        io.confluent.kafka.serializers.KafkaAvroSerializer.class);
// transactional API
consumerProps.put(ConsumerConfig.ISOLATION_LEVEL_CONFIG, "read_committed");
// consumer --from-beginning
consumerProps.put(ConsumerConfig.AUTO_OFFSET_RESET_CONFIG, "earliest");
consumerProps.put(ConsumerConfig.SESSION_TIMEOUT_MS_CONFIG, "10000");
consumerProps.put(ConsumerConfig.ENABLE_AUTO_COMMIT_CONFIG, false);
consumerProps.put("zookeeper.connect", CLUSTER.zookeeperConnect());
consumerProps.put("schema.registry.url", CLUSTER.schemaRegistryUrl());
final KafkaConsumer<GenericRecord, GenericRecord> consumer = new KafkaConsumer<GenericRecord, GenericRecord>(consumerProps);
consumer.subscribe(Collections.singletonList(inputTopic));

but failed with error

org.apache.kafka.common.KafkaException: Failed to construct kafka consumer
    at org.apache.kafka.clients.consumer.KafkaConsumer.<init>(KafkaConsumer.java:765)
    at org.apache.kafka.clients.consumer.KafkaConsumer.<init>(KafkaConsumer.java:633)
    at org.apache.kafka.clients.consumer.KafkaConsumer.<init>(KafkaConsumer.java:615)
    at com.telefonica.app.test_consumer.KafkaETLConsumerTest.testRunConsumer(KafkaETLConsumerTest.java:192)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at junit.framework.TestCase.runTest(TestCase.java:176)
    at junit.framework.TestCase.runBare(TestCase.java:141)
    at junit.framework.TestResult$1.protect(TestResult.java:122)
    at junit.framework.TestResult.runProtected(TestResult.java:142)
    at junit.framework.TestResult.run(TestResult.java:125)
    at junit.framework.TestCase.run(TestCase.java:129)
    at junit.framework.TestSuite.runTest(TestSuite.java:252)
    at junit.framework.TestSuite.run(TestSuite.java:247)
    at org.junit.internal.runners.JUnit38ClassRunner.run(JUnit38ClassRunner.java:86)
    at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:86)
    at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:539)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:761)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:461)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:207)
Caused by: org.apache.kafka.common.KafkaException: io.confluent.kafka.serializers.KafkaAvroSerializer is not an instance of org.apache.kafka.common.serialization.Deserializer
    at org.apache.kafka.common.config.AbstractConfig.getConfiguredInstance(AbstractConfig.java:248)
    at org.apache.kafka.clients.consumer.KafkaConsumer.<init>(KafkaConsumer.java:673)
    ... 22 more

confluent version 3.0.0

Answer 1

The problem is here:

consumerProps.put(ConsumerConfig.KEY_DESERIALIZER_CLASS_CONFIG,
        io.confluent.kafka.serializers.KafkaAvroSerializer.class);
consumerProps.put(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG,
        io.confluent.kafka.serializers.KafkaAvroSerializer.class);

Note that you are passing a Serializer class to a Deserializer config. Which is exactly what the exception says:

io.confluent.kafka.serializers.KafkaAvroSerializer is not an instance of org.apache.kafka.common.serialization.Deserializer

A serializer is not a deserializer.

Try:

consumerProps.put(ConsumerConfig.KEY_DESERIALIZER_CLASS_CONFIG,
            io.confluent.kafka.serializers.KafkaAvroDeserializer.class);
    consumerProps.put(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG,
            io.confluent.kafka.serializers.KafkaAvroDeserializer.class);