https://docs.spring.io/spring-cloud-stream/docs/current/reference/html/spring-cloud-stream.html#_batch_consumers
    // spring.cloud.stream.bindings.<binding-name>.consumer.batch-mode=true
    @Bean
    public Function<List<Person>, Person> findFirstPerson() {
        return persons -> persons.get(0);
    }
https://docs.spring.io/spring-cloud-stream/docs/current/reference/html/spring-cloud-stream.html#_batch_producers
    @Bean
    public Function<String, List<Message<String>>> batch() {
      return p -> {
        List<Message<String>> list = new ArrayList<>();
        list.add(MessageBuilder.withPayload(p + ":1").build());
        list.add(MessageBuilder.withPayload(p + ":2").build());
        list.add(MessageBuilder.withPayload(p + ":3").build());
        list.add(MessageBuilder.withPayload(p + ":4").build());
        return list;
      };
    }