The first step in writing messages to Kafka is to create a producer object with the properties you want to pass to the producer. A Kafka producer has three mandatory properties:

• bootstrap.servers: list of host:port pairs of brokers that the producer will use to establish initial connection to the Kafka cluster. This list doesn’t need to include all brokers, since the producer will get more information after the initial connection. But it is rec‐ ommended to include at least two, so in case one broker goes down, the producer will still be able to connect to the cluster.

• key.serializer: name of a class that will be used to serialize the keys of the records we will pro‐ duce to Kafka. Kafka brokers expect byte arrays as keys and values of messages. However, the producer interface allows, using parameterized types, any Java object to be sent as a key and value. This makes for very readable code, but it also means that the producer has to know how to convert these objects to byte arrays. key.serializer should be set to a name of a class that implements the org.apache.kafka.common.serialization.Serializer interface. The producer will use this class to serialize the key object to a byte array. The Kafka client pack‐ age includes ByteArraySerializer (which doesn’t do much), StringSerializer, and IntegerSerializer, so if you use common types, there is no need to implement your own serializers. Setting key.serializer is required even if you intend to send only values.

• value.serializer: name of a class that will be used to serialize the values of the records we will pro‐ duce to Kafka. The same way you set key.serializer to a name of a class that will serialize the message key object to a byte array, you set value.serializer to a class that will serialize the message value object.

Send Message Type

• Fire-and-forget: we send a message to the server and don’t really care if it arrives succesfully or not. Most of the time, it will arrive successfully, since Kafka is highly available and the producer will retry sending messages automatically. However, some mes‐ sages will get lost using this method.

• Synchronous send: we send a message, the send() method returns a Future object, and we use get() to wait on the future and see if the send() was successful or not.

• Asynchronous send: we call the send() method with a callback function, which gets triggered when it receives a response from the Kafka broker.

Source: confluent-kafka-definitive-guide-complete