找不到 Spring kafka AVRO 生成的类

Question

I'm using confluent JDBC connector to connect to a postgres database to retrieve changes and put them in a kafka topic. Now I want to consume these messages with a spring boot consumer. These messages are in AVRO format. I have the schema from the connector and generated a POJO class for it with the avro maven plugin.

But when the listener starts there are only the following error

   java.lang.IllegalStateException: This error handler cannot process 'SerializationException's directly; please consider configuring an 'ErrorHandlingDeserializer' in the value and/or key deserializer
       at org.springframework.kafka.listener.SeekUtils.seekOrRecover(SeekUtils.java:194) ~[spring-kafka-2.7.2.jar:2.7.2]
       at org.springframework.kafka.listener.SeekToCurrentErrorHandler.handle(SeekToCurrentErrorHandler.java:112) ~[spring-kafka-2.7.2.jar:2.7.2]
       at org.springframework.kafka.listener.KafkaMessageListenerContainer$ListenerConsumer.handleConsumerException(KafkaMessageListenerContainer.java:1598) ~[spring-kafka-2.7.2.jar:2.7.2]
       at org.springframework.kafka.listener.KafkaMessageListenerContainer$ListenerConsumer.run(KafkaMessageListenerContainer.java:1210) ~[spring-kafka-2.7.2.jar:2.7.2]
       at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:515) ~[na:na]
       at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264) ~[na:na]
       at java.base/java.lang.Thread.run(Thread.java:832) ~[na:na]
   Caused by: org.apache.kafka.common.errors.SerializationException: Error deserializing key/value for partition ps_git_repo-0 at offset 0. If needed, please seek past the record to continue consumption.
   Caused by: org.apache.kafka.common.errors.SerializationException: Could not find class ps_git_repo specified in writer's schema whilst finding reader's schema for a SpecificRecord.

When I do not use avro to deserialise the data then I will receive data but unreadable.

In the pom.xml I have the following dependencies

    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
    <dependency>
        <groupId>org.springframework.kafka</groupId>
        <artifactId>spring-kafka</artifactId>
    </dependency>
    
    <dependency>
        <groupId>org.apache.avro</groupId>
        <artifactId>avro</artifactId>
        <version>1.10.2</version>
    </dependency>
    <dependency>
        <groupId>io.confluent</groupId>
        <artifactId>kafka-avro-serializer</artifactId>
        <version>6.2.0</version>
        <exclusions>
            <exclusion>
                <artifactId>netty</artifactId>
                <groupId>io.netty</groupId>
            </exclusion>
        </exclusions>
    </dependency>

and in the application.properties i've added the deserialiser and schema registry url.

    spring.kafka.consumer.key-deserializer = org.apache.kafka.common.serialization.StringDeserializer
    spring.kafka.consumer.value-deserializer = io.confluent.kafka.serializers.KafkaAvroDeserializer
    spring.kafka.bootstrap-servers = http://localhost:9092
    spring.kafka.consumer.properties.specific.avro.reader = true
    spring.kafka.consumer.properties.schema.registry.url = http://localhost:8081

In the build I use the avro maven plugin to generate a POJO from the schema created by the connector.

plugin in pom.xml

    <plugin>
        <groupId>org.apache.avro</groupId>
        <artifactId>avro-maven-plugin</artifactId>
        <version>1.10.2</version>
        <executions>
            <execution>
                <phase>generate-sources</phase>
                <goals>
                    <goal>schema</goal>
                </goals>
                <configuration>
                    <sourceDirectory>${project.basedir}/src/main/avro/</sourceDirectory>
                    <outputDirectory>${project.basedir}/src/main/java/</outputDirectory>
                    <stringType>String</stringType>
                </configuration>
            </execution>
        </executions>
    </plugin>

I've put the following schema into the folder and generate to pojo with mvn generate-sources

Schema.avsc

    {
      "connect.name": "ps_git_repo",
      "fields": [
        {
          "name": "id",
          "type": "long"
        },
        {
          "default": null,
          "name": "name",
          "type": [
            "null",
            "string"
          ]
        }
      ],
      "name": "ps_git_repo",
      "namespace": "com.company.api.kafkademo",
      "type": "record"
    }

I get the ps_git_repo.java class in the correct then I have this listener to retrieve the messages.

    @SpringBootApplication
    @EnableKafka
    public class KafkaDemoApplication {
    
        @KafkaListener(groupId = "test123", topics = "ps_git_repo_test")
        public void handleMessage(ps_git_repo message) {
            System.out.println(message);
        }
    
        public static void main(String[] args) {
            SpringApplication.run(KafkaDemoApplication.class, args);
        }
    
    }

The schema cannot be found.

Does anybody know what is wrong?

Answer 1

The deserialiser used the connect.name field instead of the namespace to find the correct class.

I've added the following lines to the config of the JDBC_connector to let the connector generate the correct namespace

"transforms":"AddNamespace",
"transforms.AddNamespace.type":"org.apache.kafka.connect.transforms.SetSchemaMetadata$Value",
"transforms.AddNamespace.schema.name": "com.company.api.kafkademo.ps_git_repo"