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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i still prefer the Promise myself.  It's just easier to understand and work with (and native to JavaScript at this point).

When you say something like "An Observable can do everything a Promise can but not the other way around"....you should be saying "both can be used to achieve the same async activity in JavaScript

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

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The difference between heap and stack is how the memory is used.

Heap memory is used to store objects you create when your program executes.  It exists as long as your application is running.

Stack memory is used to store primitive data types and references (to things stored in the heap) when your program executes.  It is thread specific.

Blocks of memory are added and removed from the stack as your program executes.  They are created in a LIFO (last in first out) fashion when a method is invoked.  They are released when the method has finished execution.

I'm a novice Java developer and just getting my feet wet with memory management.  Can someone explain heap vs stack and how these work?

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ngOnChanges() == useEffect() in React???

i think the way Angular handles change events is much simpler than ReactJS.  While these ngonchange examples may seem a bit overboard for JavaScript, it's still easier to understand these life cycle hooks than functional components in React (in my opinion).

Does anyone know what is more performant when it comes to things like React hooks (useEffect, useState) etc and things like ngOnChanges???

Steve Jennings

People often get confused when they see ngOnChanges fire before ngOnInit. At a high level you would assume ngOnInit is the first thing called when a component is rendered.

This post does a good job of emphasizing the fact that ngOnChanges is linked to children components and their bound @Input properties.  When you initialize a child component from a parent, you are setting the component's @Input properties as part of the component's initialization....

A child component's @Input properties are updated even before the component is initialized...

Alexander Joseph

hoopmiester

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You should ALWAYS use SimpleChanges with these lifecycle hooks...

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