Writing to Kafka Topics
- Julia Damerow
Analytics
The setup for this tutorial is the same as for Listening to Kafka Topics. Please refer to its "Dependencies" section for required libraries.
The KafkaTemplate
Writing to a Kafka topic is pretty straight forward. You will need a KafkaTemplate that you can create as follows.
In a Spring managed class, add a new KafkaTemplate class variable:
private KafkaTemplate<Integer, String> template;
Instantiate this variable in a post-construct method:
@PostConstruct
private void init() {
Map<String, Object> senderProps = senderProps();
ProducerFactory<Integer, String> pf =
new DefaultKafkaProducerFactory<Integer, String>(senderProps);
template = new KafkaTemplate<>(pf);
}
where senderProps() is a method that looks like the following:
private Map<String, Object> senderProps() {
Map<String, Object> props = new HashMap<>();
props.put(ProducerConfig.CLIENT_ID_CONFIG, "test.app.producer");
props.put(ProducerConfig.BOOTSTRAP_SERVERS_CONFIG, "localhost:9092");
props.put(ProducerConfig.RETRIES_CONFIG, 0);
props.put(ProducerConfig.BATCH_SIZE_CONFIG, 16384);
props.put(ProducerConfig.LINGER_MS_CONFIG, 1);
props.put(ProducerConfig.BUFFER_MEMORY_CONFIG, 33554432);
props.put(ProducerConfig.KEY_SERIALIZER_CLASS_CONFIG, IntegerSerializer.class);
props.put(ProducerConfig.VALUE_SERIALIZER_CLASS_CONFIG, StringSerializer.class);
return props;
}
Make sure that your client id is unique and that the bootstrap servers config points to your Kafka instance. Depending on your use-case you can change the configurations as needed.
Sending messages
Once this setup is complete, you can send messages to Kafka with one line like this:
template.send("topic", "msg");
where "topic" is the topic you want to send a message to, and "msg" is the message.