You can autowire the following bean and consult its javadoc for how to use it:
@Autowired
private ITransactionalKafkaMessageSender transactionalKafkaMessageSender;
You may also want to use the following to create Json messages without much effort:
@Autowired
private ITkmsMessageFactory tkmsMessageFactory;
Most common use case will be sending a single message:
transactionalKafkaMessageSender.sendMessage(tkmsMessageFactory.createJsonMessage(value).setTopic(topic).setKey(key));