Is Kafka a database?

A look at event driven vs RESTful API design in microservice architecture including best practices and use cases for each.

Event Driven vs REST in Microservice Architecture

REST vs event-driven architecture?

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:

Spring Boot Kafka Consumer example including consumer offsets and multiple consumer examples.

Spring Boot Kafka Consumer

The Promise is still relevant and great for async operations where you are only concerned with the result of one async operation.  While the observable handles this well with Angular, it's still perfectly reasonable to use the Promise library for http requests, etc.

stackchief

Quickly understand JavaScript observables.  Implement the Observable class from scratch and understand what makes observables different from promises.

JavaScript Observables in 5 Minutes

How is index performance achieved in MongoDB?

What are KafkaListener Annotation Properties?

it generates your one to one relationships like magic...

How does a @OneToOne relationship work in Spring Data JPA?

Confused? Chicken before the egg problem?

Yes. Turns out native code/operations are utilized to load initial libraries used by JRE.

Once the main class is located, its dependencies (or the classes it uses) are loaded lazily (dynamically)

This means classes are stored and cached in memory only when they are needed.

This is what makes java a "dynamically compiled" language.  Unlike a statically compiled language like C++, Java doesn't compile everything into bytecode upfront.  Instead it converts class definitions to byte code and loads them into memory.

Learning2Code

Is Kafka a database?

Event Driven vs REST in Microservice Architecture

REST vs event-driven architecture?

Spring Boot Kafka Consumer

JavaScript Observables in 5 Minutes

How is index performance achieved in MongoDB?

What are KafkaListener Annotation Properties?

How does a @OneToOne relationship work in Spring Data JPA?

When are classes loaded in Java?

Learning2Code

Is Kafka a database?

Event Driven vs REST in Microservice Architecture

REST vs event-driven architecture?

Spring Boot Kafka Consumer

JavaScript Observables in 5 Minutes

How is index performance achieved in MongoDB?

What are KafkaListener Annotation Properties?

How does a @OneToOne relationship work in Spring Data JPA?

When are classes loaded in Java?

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