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If you're brand new to Kafka, be sure to check out this <a id=0 href='https://www.stackchief.com/blog/Kafka%20Architecture%20Explained'>intro to Kafka architecture</a> first.

<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">

<groupId>org.springframework.boot</groupId>

<artifactId>spring-boot-starter-parent</artifactId>

<description>Demo project for Spring Boot</description>

<groupId>org.springframework.boot</groupId>

<artifactId>spring-boot-starter</artifactId>

<groupId>org.springframework.kafka</groupId>

<groupId>com.fasterxml.jackson.core</groupId>

<artifactId>jackson-databind</artifactId>

<artifactId>spring-boot-starter-test</artifactId>

<artifactId>spring-kafka-test</artifactId>

<groupId>org.springframework.boot</groupId>

<artifactId>spring-boot-maven-plugin</artifactId>

The pom.xml defines the dependencies we need for our Maven build. Notice how we include the dependencies needed for Spring Boot along with those needed for running and testing Kafka.

Note that the jackson-databind dependency is included to account for bugs in older versions of the Spring Kafka library. You may not need to include this depending on which version of Kafka you're using..

	public static void main(String[] args) {

		SpringApplication.run(DemoApplication.class, args);

The DemoApplication.java class runs our Spring Boot application.

Spring Boot automatically configures Kafka via @SpringBootApplication. With this annotation, Spring provides/configures a KafkaAutoConfiguration class for you.

import org.springframework.kafka.annotation.KafkaListener;

import org.springframework.stereotype.Component;

    public void processMessage(String content){

        System.out.println("Message received: " + content);

The Consumer.java class is what actually listens for messages. Notice how we specify the topics to listen to within the @KafkaListener annotation.

By simply using the annotations provided by the Spring Boot Kafka library, we are able to easily set up a consumer for a given topic.

spring.kafka.bootstrap-servers=localhost:9092

Thanks to auto-configuration, you only need to define a few things in application.properties to configure the consumer. Notice how our app is configured to use Kafka locally.

This example is configured to consume from a local Kafka topic.  You'll need to have Kafka installed and running locally to see messages being consumed from the Spring Boot app.

To start Kafka locally, you need to start both the Zookeeper and Kafka servers locally...

./zookeeper-server-start /usr/local/etc/kafka/zookeeper.properties

This will start the zookeeper server with the default configurations.  Please note the path to your local Kafka install may vary.

./kafka-server-start /usr/local/etc/kafka/server.properties 

This will start the Kafka server with the default configurations.  Please note the path to your local Kafka install may vary.

To test the application consumer, you'll need to produce some messages for the test topic.  To start a Kafka console producer:

./kafka-console-producer --bootstrap-server=localhost:9092 --topic test

This starts a Kafka producer for the test topic. Notice how both the bootstrap-server and topic arguments match what we've defined in our application.properties file.

Once the producer is up and running, you can send a message to the test topic like this:

If everything is working correctly, you should see the message being logged through the Spring application like this:

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What is OAuth?

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