Spring Boot | How to publish JSON messages on Apache Kafka

Last Updated : 15 Jul, 2025

Apache Kafka is a publish-subscribe messaging system. A messaging queue lets you send messages between processes, applications, and servers. In this article, we will see how to send JSON messages to Apache Kafka in a spring boot application. In order to learn how to create a spring boot project, refer to this article. The full-form of JSON is JavaScript Object Notation. JSON is a lightweight data format for data interchange which can be easily read and written by humans, easily parsed and generated by machines. Though it is derived from a subset of JavaScript, yet it is Language independent. It is a complete language-independent text format. The following steps can be followed in order to publish JSON messages to Apache Kafka:

Go to spring initializr and create a starter project with following dependencies:
- Spring Web
- Spring for Apache Kafka

Open the project in an IDE and sync the dependencies. In this article, we would be creating a student model where we would be posting the student details. Therefore, create a model class Student. Add data members and create constructor and create getters and setters. The following is the implementation of the student class:

Java

// Java program to implement a // student class // Creating a student class public class Student {  // Data members of the  // student class  int id;  String firstName;  String lastName;  // Constructor of the student  // class  public Student(int id, String firstName,  String lastName)  {  this.id = id;  this.firstName = firstName;  this.lastName = lastName;  }  // Implementing the getters  // and setters  public int getId()  {  return id;  }  public void setId(int id)  {  this.id = id;  }  public String getFirstName()  {  return firstName;  }  public void setFirstName(String firstName)  {  this.firstName = firstName;  }  public String getLastName()  {  return lastName;  }  public void setLastName(String lastName)  {  this.lastName = lastName;  } }

Now, create a new class Controller with the annotation @RestController. Create a GET API and initialize KafkaTemplate with parameter as string and model class object. The following is the implementation of the controller:

Java

// Java program to implement a // controller @RestController @RequestMapping("gfg") public class UserResource {  @Autowired  private KafkaTemplate<String, Student>  kafkaTemplate;  private static final String TOPIC  = "StudentExample";  @GetMapping("/publish/{id}/"  + "{firstName}/{lastName}")  public String post(  @PathVariable("id") final int id,  @PathVariable("firstName") final  String firstName,  @PathVariable("lastName") final  String lastName)  {  kafkaTemplate.send(  TOPIC,  new Student(  id, firstName,  lastName));  return "Published successfully";  } }

Create a class StudentConfig with the annotation @Configuration. In this class we will serialize the object of the model class.

Java

// Java program to serialize the // object of the model class @Configuration public class StudentConfig {  @Bean  public ProducerFactory<String, Student>  producerFactory()  {  // Create a map of a string  // and object  Map<String, Object> config  = new HashMap<>();  config.put(  ProducerConfig.BOOTSTRAP_SERVERS_CONFIG,  "127.0.0.1:9092");  config.put(  ProducerConfig.KEY_SERIALIZER_CLASS_CONFIG,  StringSerializer.class);  config.put(  ProducerConfig.VALUE_SERIALIZER_CLASS_CONFIG,  JsonSerializer.class);  return new DefaultKafkaProducerFactory<>(config);  }  @Bean  public KafkaTemplate<String, Student>  kafkaTemplate()  {  return new KafkaTemplate<>(  producerFactory());  } }

Now, start zookeeper and Kafka server. We need to create a new topic with the name StudentExample. To do so, open a new command prompt window and change directory to the Kafka folder.
Now, create a new topic using the command given below:
For Mac and Linux: bin/kafka-topics.sh --create --zookeeper localhost:2181 --replication-factor 1 --partitions 1 --topic topic_name For Windows: .\bin\windows\kafka-topics.bat --create --zookeeper localhost:2181 --replication-factor 1 --partitions 1 --topic topic_name
Now to see the messages on the Kafka server in the real-time, use the command below:
For Mac and Linux: bin/kafka-console-consumer.sh --bootstrap-server localhost:9092 --topic topic_name --from-beginning For Windows: .\bin\windows\kafka-console-consumer.bat --bootstrap-server localhost:9092 --topic topic_name --from-beginning
Run the application and call the API as:
localhost:8080/gfg/publish/{id}/{first name}/{last name}
Note: If a different port has been used, then replace the port with 8080.