Spring Boot - Apache Kafka

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Apache Kafka is an open source project used to publish and subscribe the messages based on the fault-tolerant messaging system. It is fast, scalable and distributed by design. If you are a beginner to Kafka, or want to gain a better understanding on it, please refer to this link − www.tutorialspoint.com/apache_kafka/

In this chapter, we are going to see how to implement the Apache Kafka in Spring Boot application.

Configuring Kafka

First, download the Spring Boot project from Spring Initializer page www.start.spring.io and choose the following dependencies −

  • Spring for Apache Kafka
Creating Kafka Project

First, we need to add the Spring Kafka dependency in our build configuration file.

Maven users can add the following dependency in the pom.xml file.

<dependency>
   <groupId>org.springframework.kafka</groupId>
   <artifactId>spring-kafka</artifactId>
</dependency>

Gradle users can add the following dependency in the build.gradle file.

compile group: 'org.springframework.kafka', name: 'spring-kafka'

Producing Messages

To produce messages into Apache Kafka, we need to define the Configuration class for Producer configuration as shown −

KafkaProducerConfig.java

package com.tutorialspoint.kafka;

import java.util.HashMap;
import java.util.Map;

import org.apache.kafka.clients.producer.ProducerConfig;
import org.apache.kafka.common.serialization.StringSerializer;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.kafka.core.DefaultKafkaProducerFactory;
import org.springframework.kafka.core.KafkaTemplate;
import org.springframework.kafka.core.ProducerFactory;

@Configuration
public class KafkaProducerConfig {
   @Bean
   ProducerFactory<String, String> producerFactory() {
      Map<String, Object> configProps = new HashMap<>();
      configProps.put(ProducerConfig.BOOTSTRAP_SERVERS_CONFIG, "localhost:9092");
      configProps.put(ProducerConfig.KEY_SERIALIZER_CLASS_CONFIG, StringSerializer.class);
      configProps.put(ProducerConfig.VALUE_SERIALIZER_CLASS_CONFIG, StringSerializer.class);
      return new DefaultKafkaProducerFactory<>(configProps);
   }
   @Bean
   KafkaTemplate<String, String> kafkaTemplate() {
      return new KafkaTemplate<>(producerFactory());
   }
}

To publish a message, auto wire the Kafka Template object and produce the message as shown.

@Autowired
private KafkaTemplate<String, String> kafkaTemplate;
 
public void sendMessage(String msg) {
   kafkaTemplate.send(topicName, msg);
}

Consuming a Message

To consume messages, we need to write a Consumer configuration class file as shown below.

KafkaProducerConfig.java

package com.tutorialspoint.kafka;

import java.util.HashMap;
import java.util.Map;

import org.apache.kafka.clients.consumer.ConsumerConfig;
import org.apache.kafka.common.serialization.StringDeserializer;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.kafka.annotation.EnableKafka;
import org.springframework.kafka.config.ConcurrentKafkaListenerContainerFactory;
import org.springframework.kafka.core.ConsumerFactory;
import org.springframework.kafka.core.DefaultKafkaConsumerFactory;

@EnableKafka
@Configuration
public class KafkaConsumerConfig {
   @Bean
   public ConsumerFactory<String, String> consumerFactory() {
      Map<String, Object> props = new HashMap<>();
      props.put(ConsumerConfig.BOOTSTRAP_SERVERS_CONFIG, "localhost:2181");
      props.put(ConsumerConfig.GROUP_ID_CONFIG, "group-id");
      props.put(ConsumerConfig.KEY_DESERIALIZER_CLASS_CONFIG, StringDeserializer.class);
      props.put(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG, StringDeserializer.class);
      return new DefaultKafkaConsumerFactory<>(props);
   }
   @Bean
   public ConcurrentKafkaListenerContainerFactory<String, String> kafkaListenerContainerFactory() {
      ConcurrentKafkaListenerContainerFactory<String, String> 
      factory = new ConcurrentKafkaListenerContainerFactory<>();
      factory.setConsumerFactory(consumerFactory());
      return factory;
   }
}

Next, write a Listener to listen to the messages.

@KafkaListener(topics = "tutorialspoint", groupId = "group-id")
public void listen(String message) {
   System.out.println("Received Messasge in group - group-id: " + message);
}

Let us call the sendMessage() method from ApplicationRunner class run method from the main Spring Boot application class file and consume the message from the same class file.

Your main Spring Boot application class file code is given below −

KafkaDemoApplication.java

package com.tutorialspoint.kafka;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.ApplicationArguments;
import org.springframework.boot.ApplicationRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.kafka.annotation.KafkaListener;
import org.springframework.kafka.core.KafkaTemplate;

@SpringBootApplication
public class KafkaDemoApplication implements ApplicationRunner {
   @Autowired
   private KafkaTemplate<String, String> kafkaTemplate;

   public void sendMessage(String msg) {
      kafkaTemplate.send("tutorialspoint", msg);
   }
   public static void main(String[] args) {
      SpringApplication.run(KafkaDemoApplication.class, args);
   }
   @KafkaListener(topics = "tutorialspoint", groupId = "group-id")
   public void listen(String message) {
      System.out.println("Received Messasge in group - group-id: " + message);
   }
   @Override
   public void run(ApplicationArguments args) throws Exception {
      sendMessage("Hi Welcome to Spring For Apache Kafka");
   }
}

The code for complete build configuration file is given below.

Maven pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
   xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
   <modelVersion>4.0.0</modelVersion>
   <parent>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-parent</artifactId>
      <version>3.3.4</version>
      <relativePath/> <!-- lookup parent from repository -->
   </parent>
   <groupId>com.tutorialspoint</groupId>
   <artifactId>kafka</artifactId>
   <version>0.0.1-SNAPSHOT</version>
   <name>kafka</name>
   <description>Demo project for Spring Boot</description>
   <url/>
   <licenses>
      <license/>
   </licenses>
   <developers>
      <developer/>
   </developers>
   <scm>
      <connection/>
      <developerConnection/>
      <tag/>
      <url/>
   </scm>
   <properties>
      <java.version>21</java.version>
   </properties>
   <dependencies>
      <dependency>
         <groupId>org.springframework.boot</groupId>
         <artifactId>spring-boot-starter</artifactId>
      </dependency>
      <dependency>
         <groupId>org.springframework.kafka</groupId>
         <artifactId>spring-kafka</artifactId>
      </dependency>
      <dependency>
         <groupId>org.springframework.boot</groupId>
         <artifactId>spring-boot-starter-test</artifactId>
         <scope>test</scope>
      </dependency>
      <dependency>
         <groupId>org.springframework.kafka</groupId>
         <artifactId>spring-kafka-test</artifactId>
         <scope>test</scope>
      </dependency>
   </dependencies>
   <build>
      <plugins>
         <plugin>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-maven-plugin</artifactId>
         </plugin>
      </plugins>
   </build>
</project>

Gradle build.gradle

buildscript {
   ext {
      springBootVersion = '3.3.4'
   }
   repositories {
      mavenCentral()
   }
   dependencies {
      classpath("org.springframework.boot:spring-boot-gradle-plugin:${springBootVersion}")
   }
}

apply plugin: 'java'
apply plugin: 'eclipse'
apply plugin: 'org.springframework.boot'

group = 'com.tutorialspoint'
version = '0.0.1-SNAPSHOT'
sourceCompatibility = 1.8

repositories {
   mavenCentral()
}
dependencies {
   compile('org.springframework.boot:spring-boot-starter')
   compile group: 'org.springframework.kafka', name: 'spring-kafka')
   testCompile('org.springframework.boot:spring-boot-starter-test')
   testCompile('org.springframework.kafka:spring-kafka-test')
}

Now, create an executable JAR file, and run the Spring Boot application by using the below Maven or Gradle commands as shown −

For Maven, use the command as shown −

mvn clean install

After BUILD SUCCESS, you can find the JAR file under the target directory.

For Gradle, use the command as shown −

gradle clean build

After BUILD SUCCESSFUL, you can find the JAR file under the build/libs directory.

Run the JAR file by using the command given here −

java jar <JARFILE>

You can see the output in console window.


  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/

[32m :: Spring Boot :: [39m              [2m (v3.3.4)[0;39m

[2m2024-09-24T11:51:15.187+05:30[0;39m [32m INFO[0;39m [35m20404[0;39m [2m---[0;39m [2m[kafka] [           main][0;39m [2m[0;39m[36mc.t.kafka.KafkaApplication              [0;39m [2m:[0;39m Starting KafkaApplication using Java 21.0.3 with PID 20404 (E:\Dev\kafka\target\classes started by Tutorialspoint in E:\Dev\kafka)
[2m2024-09-24T11:51:15.189+05:30[0;39m [32m INFO[0;39m [35m20404[0;39m [2m---[0;39m [2m[kafka] [           main][0;39m [2m[0;39m[36mc.t.kafka.KafkaApplication              [0;39m [2m:[0;39m No active profile set, falling back to 1 default profile: "default"
[2m2024-09-24T11:51:16.022+05:30[0;39m [32m INFO[0;39m [35m20404[0;39m [2m---[0;39m [2m[kafka] [           main][0;39m [2m[0;39m[36mo.a.k.clients.consumer.ConsumerConfig   [0;39m [2m:[0;39m ConsumerConfig values: 
	allow.auto.create.topics = true
	auto.commit.interval.ms = 5000
	auto.include.jmx.reporter = true
	auto.offset.reset = latest
	bootstrap.servers = [localhost:2181]
	...
	ssl.trustmanager.algorithm = PKIX
	ssl.truststore.certificates = null
	ssl.truststore.location = null
	ssl.truststore.password = null
	ssl.truststore.type = JKS
	value.deserializer = class org.apache.kafka.common.serialization.StringDeserializer

[2m2024-09-24T11:51:16.080+05:30[0;39m [32m INFO[0;39m [35m20404[0;39m [2m---[0;39m [2m[kafka] [           main][0;39m [2m[0;39m[36mo.a.k.c.t.i.KafkaMetricsCollector       [0;39m [2m:[0;39m initializing Kafka metrics collector
[2m2024-09-24T11:51:16.206+05:30[0;39m [32m INFO[0;39m [35m20404[0;39m [2m---[0;39m [2m[kafka] [           main][0;39m 
...
[2m2024-09-24T11:51:16.247+05:30[0;39m [32m INFO[0;39m [35m20404[0;39m [2m---[0;39m [2m[kafka] [           main][0;39m [2m[0;39m[36mo.a.k.clients.producer.ProducerConfig   [0;39m [2m:[0;39m ProducerConfig values: 
	acks = -1
	auto.include.jmx.reporter = true
	batch.size = 16384
	bootstrap.servers = [localhost:9092]
	buffer.memory = 33554432
	client.dns.lookup = use_all_dns_ips
	client.id = kafka-producer-1
    ...
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