A Java Lagom service which only consumes from Kafka topic (Subscriber only service)

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Subscriber only service means an application which only consumes, does not produce.

We have generally seen the applications which both produces and consumes data from a Kafka topic but sometimes we need to write an application which only consumes data i.e. consumes data from a 3rd party service. So in this blog I am going to explain how to write a Lagom service which only consumes data (does not produce any data).

Add below dependency to your impl pom.xml:

We need to create a separate module kafka-connect in Lagom project. That module will contain a Service Descriptor declaring the topic service will consume from.

Then, add kafka-connect dependency in impl module:

Then, to consume data implement consumer as below:

Finally, you need to bind KafkaConsumer as Eager singleton and KafkaService in HelloModule:

To connect with external kafka, made below changes in root pom:

and, add below configuration in application.conf file:

That’s it. Now you need to start zookeper and Kafka at your local machine, create topic greetings and then produce any message in Kafka. As a message will be produced in Kafka, consumer will consume data and will print the message.

I hope you enjoyed the blog.

You can get full code here.

Written by 

Rishi is a tech enthusiast with having around 10 years of experience who loves to solve complex problems with pure quality. He is a functional programmer and loves to learn new trending technologies. His leadership skill is well prooven and has delivered multiple distributed applications with high scalability and availability by keeping the Reactive principles in mind. He is well versed with Scala, Akka, Akka HTTP, Akka Streams, Java8, Reactive principles, Microservice architecture, Async programming, functional programming, distributed systems, AWS, docker.

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