title: Spring-Kafka cannot convert AVRO GenericData.Record to Acknowledgment
body: <p>Using Spring Boot, I am trying to set up my Kafka consumers in batch receiving mode:</p>
  
  <pre><code>@Bean
  public ConcurrentKafkaListenerContainerFactory&lt;String, GenericData.Record&gt; kafkaListenerContainerFactory() {
      ConcurrentKafkaListenerContainerFactory&lt;String, GenericData.Record&gt; factory = new ConcurrentKafkaListenerContainerFactory&lt;&gt;();
      factory.setConsumerFactory(consumerFactory());
      factory.setMessageConverter(new StringJsonMessageConverter()); // I know this one won't work
      factory.setBatchListener(true);
      return factory;
  }
  
  @Bean
  public ConsumerFactory&lt;GenericData.Record, GenericData.Record&gt; consumerFactory() {
      Map&lt;String, Object&gt; dataRiverProps = getDataRiverProps();
      dataRiverProps.put(ConsumerConfig.BOOTSTRAP_SERVERS_CONFIG, env.getProperty("bootstrap.servers"));
      return new DefaultKafkaConsumerFactory&lt;&gt;(dataRiverProps);
  }
  </code></pre>
  
  <p>And this is what the actual consumer looks like:</p>
  
  <pre><code>@KafkaListener(topics = "#{'${kafka.topics}'.split(',')}", containerFactory = 'kafkaListenerContainerFactory')
  public void consumeAvro(List&lt;GenericData.Record&gt; list, Acknowledgment ack) {
      messageProcessor.addMessageBatchToExecutor(list);
      while (messageProcessor.getTaskSize() &gt; EXECUTOR_TASK_COUNT_THRESHOLD) {
          try {
              Thread.sleep(100);
          } catch (InterruptedException e) {
              LOGGER_ERROR.error(ExceptionUtils.getStackTrace(e.getCause()));
          }
      }
  }
  </code></pre>
  
  <p>The exceptions I am getting look like this:</p>
  
  <pre><code>nested exception is org.springframework.core.convert.ConverterNotFoundException: No converter found capable of converting from type [org.apache.avro.generic.GenericData$Record] to type [org.springframework.kafka.support.Acknowledgment]
          at org.springframework.core.convert.support.ConversionUtils.invokeConverter(ConversionUtils.java:46)
          at org.springframework.core.convert.support.GenericConversionService.convert(GenericConversionService.java:191)
          at org.springframework.core.convert.support.GenericConversionService.convert(GenericConversionService.java:174)
          at org.springframework.messaging.converter.GenericMessageConverter.fromMessage(GenericMessageConverter.java:66)
  </code></pre>
  
  <p>The Kafka messages are AVRO messages, and I would like to retrieve them as JSON strings. Is there a ready-for-use AVRO converter for GenericData.Record that I can plug in the ConcurrentKafkaListenerContainerFactory? Thanks!</p>