Micronaut Kafka Consumer Producer example.

Micronaut Kafka consumer and producer example.

Micronaut is a java framework and it’s been popular to develop microservice-based applications because of lower memory footprint and fast startup.

In this article, we will see how to write down simple Kafka consumers and producers using the micronaut framework. 

You can read my articles on micronaut framework on https://www.techwasti.com/

Start generating project using https://micronaut.io/launch/

You can create a project either using the launch site or using CLI tool.

$ mn create-app techwastikafkaexample --features kafka

Micronaut version for this demo is 2.0.0 and Java 8.

generating project and adding Kafka profile CLI provides powerful option such as;

$ mn create-app techwasti-kafka-service --profile kafka


  1. Java programming
  2. Kafka
  3. Micronaut

I am assuming the people. You know about this if you don’t know then learn it.

Micronaut features dedicated support for defining both Kafka Producer and Consumer instances.

Kafka Producer:-

We will create one simple Producer using annotation.

package com.techwasti.kafkaex;

import io.micronaut.configuration.kafka.annotation.KafkaClient;
import io.micronaut.configuration.kafka.annotation.KafkaKey;
import io.micronaut.configuration.kafka.annotation.Topic;

public interface GreetMessageClient {

    // greet is a kafka topic
    void sendGreetMessage(@KafkaKey String day, String message);

    void sendGreetMessage(@Topic String topic, @KafkaKey String day, String message);

@KafkaClient annotation is used to mark this is the kafka client.

@Topic annotation is indicated, on which topic message should get published. 

@Kafkakey annotation is to have a message key.

In the above code snippet we have defined two methods:

  1. In the first method accepting two arguments key and value and topic name is annotated using @Topic. 
  2. In the second method instead of annotating the topic name, we are accepting the topic name in the argument. 

If you omit the @KafkaKey then it’s null.

As we are aware of the beauty of micronaut framework, it will produce an implementation of the above client interface. We can retrieve this instance either by looking up the bean from ApplicationContext or by injecting the bean using @Inject. 

GreetMessageClient client = applicationContext.getBean(GreetMessageClient.class); client.sendProduct("Thursday", "Good morning");

Now our producer is ready and we sent a successful message as well.

Let us create Kafka Consumer.

Kafka Consumer:-

As we have seen a couple of annotations to create a producer and produce a message over a topic. The same way we have @KafkaListener annotation to create a kafka consumer.

package com.techwasti.kafkaex;

import io.micronaut.configuration.kafka.annotation.KafkaKey;
import io.micronaut.configuration.kafka.annotation.KafkaListener;
import io.micronaut.configuration.kafka.annotation.OffsetReset;
import io.micronaut.configuration.kafka.annotation.Topic;

@KafkaListener(offsetReset = OffsetReset.EARLIEST)
public class GreetMessageConsumer {

    public void receive(@KafkaKey String day, String message) {
        System.out.println("Got Message for the  - " + day + " and Message is  " + message);

@KafkaListener is used to indicate this is kafka consumer and while reading a message from the topic “greet” and offset should be earliest this will start reading a message from the start.

receive method having two arguments one is key and another one is the message. 

This is a simple example of having kafka consumers and producers. 

Advanced Options for producer and consumer:

@Header: To add a header to kafka message. 

When we want to add some header into the kafka producer when we produce a message, let us say we want to add authentication token while publishing message over kafka in this case 


@Header(name = “JWT-Token”, value = “${my.authentication.token}”)

Also, you can pass the header as a method argument the same as a topic name. 

@Body: to explicitly indicate the message body.

Generally, the value sent by the producer resolved using @Body annotation only but if we haven’t mentioned it then the first argument resolved as message body. 


void sendGreetMessage(@KafkaKey String day, String message);


void sendGreetMessage(@KafkaKey String day, @Body String message);

For more such things please visit micronaut documentation.



Spring Boot Neo4j Reactive CRUD.

This article is about the spring data for neo4j database. Neo4j is a popular graph database.


Spring Data Neo4j module is there which is support only imperative style and currently, it’s only in support and maintenance.


You head this article that means you at least heard about Neo4j and spring boot. below are the prerequisites

  1. Neo4j (https://neo4j.com/graphacademy/online-training/introduction-to-neo4j-40/)
  2. Installation of Neo4j on local or use Neo4j sandbox.
  3. Knowledge with spring data and spring boot.
  4. For this example, we are using JDK 11.

If you don’t know anything about the above things then I will recommend you should start exploring these things and come back.

In this example, I am using Neo4j sandbox environment: https://neo4j.com/sandbox/

Advantages of using SDN-Rx:

  1. It supports both imperative and reactive development.
  2. Built-in OGM(Object graph mapping) and very lightweight.
  3. Support immutable entities for both Java and kotlin.

Maven/Gradle Dependencies:-

Right now Spring Data Neo4j Reactive starter is not yet part of the official Spring repositories so we have to add that manually, so it won’t be available in the spring initializer website.

## maven dependency
## gradle 
dependencies {
    compile 'org.neo4j.springframework.data:spring-data-neo4j-rx-spring-boot-starter:1.1.1'

PrePare Database:-

For this article, we are using the Neo4j-standard movie graph database because it’s in small size and it’s available in your sandbox as well as in your local.

use this command to start:

:play movies

Execute the command and deck is an interactive mode, so its seamless execution. The movie database contains a database such as a movie name, release date, crew, director of movie, a rating is given by different individuals or rating companies. The minimal schema relation could be like this

(:Person {name})-[:ACTED_IN {roles}]->(:Movie {title,released})
movie DB schema

Create Project:

The best way to start with the spring boot project is start.spring.io. Create a spring boot project.

Do not choose Spring Data Neo4j here, as it will show the legacy generation of Spring Data Neo4j that has only imperative support.

Once your project is ready then add the spring data neo4j Rx dependency in your POM or build.gradle.


You can put here your database-specific configurations.


Domain Entity:

All our configurations are done now let us begin and define the domain entity object. As we stated we are using a movie database so we have to create Movie as a domain entity with few properties.

Entities are nodes.

package com.techwasti.entity;

import org.neo4j.springframework.data.core.schema.Id;
import org.neo4j.springframework.data.core.schema.Node;
import org.neo4j.springframework.data.core.schema.Property;
import org.neo4j.springframework.data.core.schema.Relationship;

import java.util.HashSet;
import java.util.Set;

import static org.neo4j.springframework.data.core.schema.Relationship.Direction.INCOMING;

public class Movie {

    private final String mtitle;

    private final String tagline;

    @Relationship(type = "ACTED_IN", direction = INCOMING)
    private Set<Person> actors = new HashSet<>();

    @Relationship(type = "DIRECTED", direction = INCOMING)
    private Set<Person> directors = new HashSet<>();

    public Movie(String title, String tagline) {
        this.mtitle = title;
        this.tagline = tagline;

    public String getTitle() {
        return mtitle;

    public String getTagline() {
        return tagline;
    public Set<Person> getActors() {
        return actors;

    public void setActors(Set<Person> actors) {
        this.actors = actors;

    public Set<Person> getDirectors() {
        return directors;

    public void setDirectors(Set<Person> directors) {
        this.directors = directors;

In the movie entity, we defined a movie name, tagline, actors, and directors.

@Node annotation marks the given class is the managed node. @Id annotation to have a unique property and then we defined different relationships using @Relationship annotation. In the same way, we have a Person entity that contains two fields.

package com.techwasti.entity;

import org.neo4j.springframework.data.core.schema.Id;
import org.neo4j.springframework.data.core.schema.Node;

public class Person {

    private final String name;

    private final Integer born;

    public Person(Integer born, String name) {
        this.born = born;
        this.name = name;

    public String getName() {
        return name;

    public Integer getBorn() {
        return born;

In these entities, we just defined one-way relation to have demonstrated things simple but you can also define an entity in such a way to fulfill two-way relationships.

Let us create a repository class then.

package com.techwasti.dao;

import com.techwasti.entity.Movie;
import org.neo4j.driver.internal.shaded.reactor.core.publisher.Mono;
import org.neo4j.springframework.data.repository.ReactiveNeo4jRepository;

public interface MovieRepository extends ReactiveNeo4jRepository<Movie, String> {
    Mono<Movie> findOneByTitle(String title);

This is to demonstrate the reactive programming style so we used here ReactiveNeo4jRepository which is reactive repository implementation.

You can hit below endpoints to see the output:

GET http://localhost:8080/movies

DELETE http://localhost:8080/movies/The Matrix

This is it for now.




Micronauts Launch: The best way to getting started.

Micronaut has launched a website to generate the Micronauts project using the website without installing the Micronauts CLI SDK.

In a couple of blogs, we have seen about Micronauts if you don’t know you can check below blog post:

Micronaut is very much similar to the spring framework. Micronaut took inference from Spring framework and most the API are in sync only, that’s why adopting Micronauts for spring developer is very easy. As we have start.spring.io to start and create spring or spring boot project on the same note Micronauts also launched website aka Micronauts launch.


As we know we can generate micronaut project using CLI but we can take same advantage using website as well.

If you see here we have different options few are listed below.

  1. Application type
  2. Java version
  3. Base Package
  4. Name of application
  5. etc

1. Application type:-

Application type where we have to specify which type of application we want such as Application (web or any other application), CLI application, Serverless function, gRPC application, and Messaging application. This application type will help us to organize the dependencies.

2. Java Version:-

Java version where we have to specify on which JDK we want to develop your application, e.g Java 8,11, 14 etc.

3. Base Package:-

Base package here we have specify our package of the application under which we want organise our classes, interfaces.

e.g com.techwasti.micronaut.demo

4. Name:-

Here we have to specify name of the application.

e.g HelloworldLaunch.

5. Micronaut Version:-

Which micronaut version our application should be compatible latest one when I am writing this blog post is 2.0.0.

6. Language:-

Select which language do you want to write down the beautiful code, right now micronaut support java, kotlin and Groovy.

7. Build Tool:-

Select which build tool either from maven or gradle.

8. Test Framework:-

Here we have a choice to select the test framework anything from the list such as Junit, Spock, and kotlintest.

9. Features:

When you click on features button one popup will launch.

In features we have different groups such as cache, config, database, etc.

10. Diff:-

This is to show the difference. This is interesting option. Shows the changes that the selected features have on an application generated without any features selected.

11. Preview:-

Another best option this site provides is the preview of your project based on your selection.

The final option is to generate the project and once you click on this are getting zip file. After zip extraction, you will get below kind of structure.

Were we have docker file, build file, gitignore along with source directory structure. Download and import this in any of your IDE(eclipse, intellij) and happy coding.

This is it for now. Let me know your finding on this if any.

Spring boot Cloud Native Buildpacks and Layered jars.

In May 2020 spring boot 2.3 is released with some interesting features. There are many but in this article, we will talk about support for building OCI images using cloud-native build packs. 

Cloud-Native BuildPacks?

These days cloud migration and in that cloud-native application development is becoming a trend.

Cloud-Native Buildpacks
transform your application source code to images that can run on any cloud.

Cloud-native buildpacks definition from From https://buildpacks.io/,

The Cloud Native Buildpacks project was initiated by Pivotal and Heroku in January 2018 and joined the Cloud Native Sandbox in October 2018. The project aims to unify the buildpack ecosystems with a platform-to-buildpack contract that is well-defined and that incorporates learnings from maintaining production-grade buildpacks for years at both Pivotal and Heroku.

credit goes to https://buildpacks.io/

Cloud-Native Buildpacks embrace modern container standards, such as the OCI(Open container initiative) image format. They take advantage of the latest capabilities of these standards, such as cross-repository blob mounting and image layer “rebasing” on Docker API v2 registries.

All the above information is from buildpack website only. The buildpack in fewer words: will transform your beautiful source code into runnable container images.

The Paketo java build is used by default to create an image.

Prerequisites for this example:

  1. Java
  2. Docker
  3. Any IDE if you want.

Note:- For this demo, I am using spring-boot:2.3.1 version, JDK-8 and maven.

and Always for spring start with https://start.spring.io/

I have imported the project into the VSCode. If you want to learn about Spring tools for Visual Studio Code, please go through this link: https://www.techwasti.com/spring-tools-4-for-visual-studio-code/

Create One REST Controller:-

As part of this article, our focus is on buildpack not on complex coding.

We have a simple controller this will return the current date.

package com.techwasti.spring.buildpackex.springboot23ocibuildpackex;

import java.util.Date;

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

public class CurrentDateController{

     public String getTodaysDate(){
        return new Date().toString();

Output: Sun Jul 19 09:00:36 IST 2020

Build the image for our app:

As mentioned above and as per the spring boot documentation, we will build an image. Package the source code and build the image as per OCI standard using the maven task.

$ mvn spring-boot:build-image

When you fire this command everything will be taken by spring boot build-image task. After a successful building image.

In your log you will see similar logs:

Successfully built image ‘docker.io/library/spring-boot23-oci-buildpack-ex:0.0.1-SNAPSHOT’

We can validate our docker image using the below command.

$ docker images| grep spring

spring-boot23-oci-buildpack-ex 0.0.1-SNAPSHOT ddabb93c2218 40 ago 231MB

Now our image is ready, let us run the image and create a container 

$ docker run -d -p 8080:8080  — name springbuildpackex spring-boot23-oci-buildpack-ex:0.0.1-SNAPSHOT

once a container ready verify using 

$ docker ps

Hit REST API endpoint http://localhost:8080/gettodaysdate

You can hit actuator endpoints 



Spring Boot 2.3.0.RC1 Paketo Java buildpack is used by default to create images.

you can check on your local docker when you fire below command you can see Paketo docker image was downloaded.

$ docker images| grep gcr
gcr.io/paketo-buildpacks/run       base-cnb                c8c8215efa6f        8 days ago          71.1MB
gcr.io/paketo-buildpacks/builder base-platform-api-0.3 e49209451fa6 40 years ago 696MB

Customize build pack configuration:

Now we have seen that by default the name of the image is based on artifactId and a tag is a version of our maven project. Image name if spring-boot23-oci-buildpack-ex 0.0.1-SNAPSHOT


In your real-life project, you would like to push the OCI image to a specific docker image registry, which is internal to your organization. Here I am using the docker hub is a public central registry. You configure parameters such as the name of the docker image in POM.xml


With these custom tags and names, I can push this image to the docker hub.

docker push docker.io/maheshwarligade/spring-boot23-oci-buildpack-ex

Using the command line as well:

$ mvn spring-boot:build-image -Dspring-boot.build-image.imageName=enterprise.com/library/domain/sspring-boot23-oci-buildpack-ex

We can also configure build packs builder to build the image using below configuration param


Proxy Configuration:

If any proxy is configured between the Docker daemon the builder runs in and network locations that build-packs download artifacts from, you will need to configure the builder to use the proxy. When using the default builder, this can be accomplished by setting the HTTPS_PROXY and/or HTTP_PROXY environment:

<HTTP_PROXY>http://proxy.example.com</HTTP_PROXY> <HTTPS_PROXY>https://proxy.example.com</HTTPS_PROXY>

Layered Jars:

We have seen above to create the image we used to build-pack, but you might not want to use build pack to build an image, perhaps we want to use some tool which is used within your organization based docker file to create an application image, Spring wanted to make it also easier to create optimized Docker images that can be built with a regular dockerfile so Spring has added support for layered jars.

basically we follow approach to create a docker image using spring boot application fat jar and add that into docker file and add a command to execute this.

The jar is organized into three main parts:

  • Classes used to bootstrap jar loading
  • Your application classes in BOOT-INF/classes
  • Dependencies in BOOT-INF/lib

Since this format is unique to Spring Boot, In spring boot in 2.3.0.M1 providing a new layout type call LAYERED_JAR

As we know about the docker file its layered file and when we rebuild image for dev purpose it should build where changes had happened instead of rebuilding the fat jar layer again and again. The layered jar type is designed to separate code based on how likely it is to change between application builds. Library code is less likely to change between builds, so it is placed in its own layers to allow tooling to re-use the layers from the cache. Application code is more likely to change between builds so it is isolated in a separate layer.

  • dependencies (for regularly released dependencies)
  • snapshot-dependencies (for snapshot dependencies)
  • resources (for static resources)
  • application (for application classes and resources)

Build the docker file 


Build jar for application

$ mvn clean package

We can have layered jar using jarmode

$ java -Djarmode=layertools -jar target/spring-boot23-oci-buildpack-ex-0.0.1-SNAPSHOT.jar list



based on this we can craft docker file which will be similar like below:

FROM adoptopenjdk:11-jre-hotspot as builder
WORKDIR application
ARG JAR_FILE=target/*.jar
COPY ${JAR_FILE} application.jar
RUN java -Djarmode=layertools -jar application.jar extract

FROM adoptopenjdk:11-jre-hotspot
WORKDIR application
COPY --from=builder application/dependencies/ ./
COPY --from=builder application/snapshot-dependencies/ ./
COPY --from=builder application/resources/ ./
COPY --from=builder application/application/ ./
ENTRYPOINT ["java", "org.springframework.boot.loader.JarLauncher"]


Here we have seen multiple ways to create an image of our spring boot application. With buildpacks, docker files, & existing plugins such as jib, there is no conclusion that which is the best way. Each approach has pros and cons and we have to use these tools based on our easiness and simplification.

Source Code: https://github.com/maheshwarLigade/spring-boot23-oci-buildpack-ex


Micronaut with Graal native image example.

As we have seen in the last couple of articles on how to create simple Micronauts application development and dockerizing it. In this article, we are gone exploring Helloworld Graal micronaut application.

Here is the definition from Wikipedia. If you are crossing this article that means you are familiar with either of the topic.

GraalVM is a Java VM and JDK based on HotSpot/OpenJDK, implemented in Java. It supports additional programming languages and execution modes, like an ahead-of-time compilation of Java applications for fast startup and low memory footprint. The first production-ready version, GraalVM 19.0, was released in May 2019.

Let us start coding and simultaneously enjoy the topic.

Create a micronaut application using CLI:

$ mn create-app helloworld-graal --features=graal-native-image

The default option is not available to add Graal support we have to use this option  — features=graal-native-image.

If you are using Java or Kotlin and IntelliJ IDEA make sure you have enabled annotation processing.

Now let us create one simple POJO class to hold Play name to make it simple.

import io.micronaut.core.annotation.Introspected;

public class Play{

    private String name;

    public Play(String name) {
        this.name = name;

    public String getName() {
        return name;

    public void setName(String name) {
        this.name = name;

@Introspected annotation is used to generate BeanIntrospection metadata at compilation time. This information is using the render the POJO as JSON using Jackson without using reflection.

Now let us create the Singelton Service class and return play name randomly.

(Note:- The play names are Marathi Play names of famous Sri Pu la Deshpande)

import javax.inject.Singleton;
import java.util.Arrays;
import java.util.List;
import java.util.Random;

public class PlayService {
// create list of plays
    private static final List<Play> PLAYS = Arrays.asList(
            new Play("Tujhe Ahe Tujpashi"),
            new Play("Sundar Mee Honar"),
            new Play("Tee Phularani"),
            new Play("Teen Paishacha Tamasha"),
            new Play("Ek Jhunj Varyashi")
 // to choose random play from PLAYS list
    public Play randomPlay() {
        return PLAYS.get(new Random().nextInt(PLAYS.size()));

Now we need a controller to serve the request of random play name from service class.

import io.micronaut.http.annotation.Controller;
import io.micronaut.http.annotation.Get;

public class PlayController {

    private final PlayService playService;

    public PlayController(PlayService playService) {
        this.playService = playService;

    public Play randomPlay() {
        return playService.randomPlay();

Created controller and injected service object using constructor injection and mapping of GET method using @Get(“/randomplay”).

Now our application is ready you can test by executing below command.

$ ./gradlew run


JSON output 


 name: “Tee Phularani”


Let us create a Graal native image.

Micronaut only supported in Java or Kotlin for graal native-image.

While creating a project we have added — features=graal-native-image this is adding three important features. 

  1. svm(Substrate VM) and graal dependencies in build.gradle.
compileOnly "org.graalvm.nativeimage:svm"
annotationProcessor "io.micronaut:micronaut-graal"

2. A Dockerfile which can be used to construct the native image executing docker-build.sh

3. A native-image.properties file in the resource directory.

Args = -H:IncludeResources=logback.xml|application.yml|bootstrap.yml \
       -H:Name=helloworld-graal \

This is very easy for developer to create a native image inside docker. Fire below two commands: 

$ ./gradlew assemble
$ ./docker-build.sh

Once image is ready we can create a container to verify our understanding. 

$ docker run -p 8080:8080 helloworld-graal

To test the application you can use curl with time:

$ time curl localhost:8080/randomplay

This is for now. You can check the time difference with native image executable and docker with a native image. 

Source code download or clone from github: https://github.com/maheshwarLigade/micronaut-examples/tree/master/helloworld-graal

Dockerise Micronaut application.

Micronauts is a java framework to develop a cloud-native microservices application easily and seamlessly. If you don’t know about Micronaut Please go through below two articles. 

In this article, we are exploring a micronaut framework and How to dockerize it. 

Let us create a small micronaut REST service application and try to dockerize it.

Micronaut provides a CLI option to create an application easily.

$ mn create-app helloworld

This will scaffold a new Gradle project. If you prefer Maven, add a --build maven parameter. If you want to create a new Groovy or Kotlin project, add a --lang parameter.

$ mn create-app --lang groovy helloworld-groovy
$ mn create-app --lang kotlin helloworld-kotlin

These options depend on you, which language are you comfortable with.

These options depend on you, which language are you comfortable with. 

Once the project is ready we can import that in your favorite editor. I am using IntelliJ.

We are using already created Hello world app, source code is available at below location you can clone


By default, micronaut app can create Docker file for you and docker file you can locate on current directory of your project <appname>/Docker 

e.g helloworld/Docker

The Default content of Docker file:

FROM adoptopenjdk/openjdk13-openj9:jdk-13.0.2_8_openj9-0.18.0-alpine-slim
COPY build/libs/helloworld-*-all.jar helloworld.jar
CMD ["java", "-Dcom.sun.management.jmxremote", "-Xmx128m", "-XX:+IdleTuningGcOnIdle", "-Xtune:virtualized", "-jar", "helloworld.jar"]

If you are familiar with docker then fine if not you can explore below article to understand docker.


Micronaut create docker file with alpine-slim 

and JDK image which is used here is unofficial.

This repo provides Unofficial AdoptOpenJDK Docker Images,

Reference:- https://hub.docker.com/r/adoptopenjdk/openjdk13-openj9

Thrid line to copy the generated jar(helloworld.jar) file and the expose default port as 8080. Last line to launch the jar file.

For this example, I am using Gradle as a build tool

$ cd helloworld
$ ./gradlew run

To test whether code is working fine or not. (curl http://localhost:8080/hello)

Now build a Docker image from the docker file for that fire below command. 

To run the application with IntelliJ IDEA, you need to enable annotation processing:

  1. open Settings → Build → Execution → Deployment → Compiler →Annotation Processors
  2. Set the checkbox Enable annotation processing

As we know micronaut CLI generates a Dockerfile by default, making it easy to package your application for a container environment such as Kubernetes.

$ docker build . -t hello-world-ex

Fire above command to create a docker image. -t 1.0.0 indicates the tag for this image. Now our image is ready to make a container from its fire below command. 

$ docker run --rm -p 8080:8080 hello-world-ex

As we have exposed 8080 port in docker file. We are doing port mapping to an external system.

to verify the docker image fire below command.

$ curl http://localhost:8080/hello

In this article, we have seen dockerizing micronaut apps. We have created helloworld application and created a docker image using the existing Docker file. You can edit the docker file and optimize it as per your requirement. 

Spring Boot Firebase CRUD

In this article, we show How to build a CRUD application using Firebase and Spring boot.

Create a Firebase project in the Firebase console:


Hit the https://console.firebase.google.com and sign up for an account.

Click the “Add Project” button from the project overview page.

Type “Firebase DB for Spring Boot” in the “Project name” field.

Click the “CREATE PROJECT” button.

Now we have created a project on Firebase, now let us add firebase to our spring boot app.

Add Firebase to your web app:

You can find your Realtime Database URL in the Database tab (DEVELOP → Database → Realtime Database → Start in test Mode ) in the Firebase console. It will be in the form of https://<databaseName>.firebaseio.com.

Create Firebase in test mode this is not useful for Prod development but for our this article we will use it in test mode which is available publicly. 

Your Database URL should look like this https://<Projectname XYZ>.firebaseio.com/

Our data is ready but still, we need a service account 

Go and click on Project settings → Service Accounts → Choose Language as Java. to copy code snippet

and Download JSON file as well by clicking on “Generate new private key”

We will also grab the admin SDK configuration snippet for java.

Then go to https://start.spring.io/ and create a project, Once the project added then open the pom.xml file and add below dependency.


Now everything is ready to Let us initialize Firebase Database.

import com.google.auth.oauth2.GoogleCredentials;
import com.google.firebase.FirebaseApp;
import com.google.firebase.FirebaseOptions;
import org.springframework.stereotype.Service;

import javax.annotation.PostConstruct;
import java.io.FileInputStream;

public class FBInitialize {

    public void initialize() {
        try {
            FileInputStream serviceAccount =
                    new FileInputStream("./serviceaccount.json");

            FirebaseOptions options = new FirebaseOptions.Builder()

        } catch (Exception e) {


I am using the existing Firebase Database.

@Service and @PostConstruct these are the two annotations from Spring Boot. 

First-line reads the configurations from the JSON file and then initializes the connection for the specified database. 

Now firebase connection is initialized then let us create CRUD operations.

Create a POJO class as a Patient

public class Patient {

    private String name;

    private int age;

    private String city;

    public Patient(String name, int age, String city) {

    public String getName() {
        return name;

    public void setName(String name) {
        this.name = name;

    public int getAge() {
        return age;

    public void setAge(int age) {
        this.age = age;

    public String getCity() {
        return city;

    public void setCity(String city) {
        this.city = city;

Create Service class

import com.google.api.core.ApiFuture;
import com.google.cloud.firestore.DocumentReference;
import com.google.cloud.firestore.DocumentSnapshot;
import com.google.cloud.firestore.Firestore;
import com.google.cloud.firestore.WriteResult;
import com.google.firebase.cloud.FirestoreClient;
import org.springframework.stereotype.Service;

import java.util.concurrent.ExecutionException;

//CRUD operations
public class PatientService {

    public static final String COL_NAME="users";

    public String savePatientDetails(Patient patient) throws InterruptedException, ExecutionException {
        Firestore dbFirestore = FirestoreClient.getFirestore();
        ApiFuture<WriteResult> collectionsApiFuture = dbFirestore.collection(COL_NAME).document(patient.getName()).set(patient);
        return collectionsApiFuture.get().getUpdateTime().toString();

    public Patient getPatientDetails(String name) throws InterruptedException, ExecutionException {
        Firestore dbFirestore = FirestoreClient.getFirestore();
        DocumentReference documentReference = dbFirestore.collection(COL_NAME).document(name);
        ApiFuture<DocumentSnapshot> future = documentReference.get();

        DocumentSnapshot document = future.get();

        Patient patient = null;

        if(document.exists()) {
            patient = document.toObject(Patient.class);
            return patient;
        }else {
            return null;

    public String updatePatientDetails(Patient person) throws InterruptedException, ExecutionException {
        Firestore dbFirestore = FirestoreClient.getFirestore();
        ApiFuture<WriteResult> collectionsApiFuture = dbFirestore.collection(COL_NAME).document(person.getName()).set(person);
        return collectionsApiFuture.get().getUpdateTime().toString();

    public String deletePatient(String name) {
        Firestore dbFirestore = FirestoreClient.getFirestore();
        ApiFuture<WriteResult> writeResult = dbFirestore.collection(COL_NAME).document(name).delete();
        return "Document with Patient ID "+name+" has been deleted";


Now we are ready with CRUD operation let us develop the REST Controller which will help us in interaction with this service layer.

Note:- You have to enable Cloud FireStore API.

Now we just need to create Controller which can handle REST request.

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.*;

import java.util.concurrent.ExecutionException;

public class PatientController {

    PatientService patientService;

    public Patient getPatient(@RequestParam String name ) throws InterruptedException, ExecutionException{
        return patientService.getPatientDetails(name);

    public String createPatient(@RequestBody Patient patient ) throws InterruptedException, ExecutionException {
        return patientService.savePatientDetails(patient);

    public String updatePatient(@RequestBody Patient patient  ) throws InterruptedException, ExecutionException {
        return patientService.updatePatientDetails(patient);

    public String deletePatient(@RequestParam String name){
        return patientService.deletePatient(name);

Now coding is done try by yourself and let’s know.

Installation of Micronaut on Mac(OSX) & Linux.

Micronaut is a full framework to develop cloud native microservice architecture based application using java, kotlin or Groovy.

Let us check the steps required to install micronaut on OSx.

Simple and effortless start on Mac OSX, Linux, you can use SDKMAN! (The Software Development Kit Manager) to download and configure any Micronaut version of your choice.


This tool makes installing of a Micronaut on any Unix based platform such as Linux, OSx.

Open a terminal and install SDKMAN,

$  curl -s https://get.sdkman.io | bash

Follow the on-screen instructions to complete installation.

Then fire below command after installation of SDKMAN to configure SDKMAN.

 $ source "$HOME/.sdkman/bin/sdkman-init.sh"

Once above two steps are in align then go and setup micrnaut using SDKMAN,

$ sdk install micronaut

After installation is complete it can be validated with below command.

$ mn --version
installation and validation of micronaut

this is the simple steps with SDKMAN.


Before installation using homebrew you should update homebrew version

$ brew update

In order to install Micronaut, run following command:

$ brew install micronaut

After installation is complete it can be validated with below command.

$ mn --version

Installing with MacPorts:

Before installing it is recommended to sync the latest Portfiles, So that there shouldn’t be any issue,

$ sudo port sync

To install Micronaut, run following command

$ sudo port install micronaut

After installation is complete it can be validated with below command.

$ mn --version

Above are they three different way we can setup micronaut framework on MacOS and linux based OS.

Spring Tools 4 for Visual Studio Code.

Visual studio code is the most popular, open-source and lightweight editor in the market. Spring boot has also another popular and powerful Framework in the Java ecosystem. It gains popularity because of simplicity and bootstrap the development. Spring boot is very handy to develop microservice-based applications and also support for cloud-native development. 

This article is for those who want to leverage their VS code editor to develop spring framework application. Spring comes up with tools to support the development of spring framework based application in VSCode.

Spring really provides the flexibility to a developer, for spring developer you don’t need any special editor, IDE or OS or any tool suite as well. 

Spring is nature’s way of saying, ‘Let’s Party!

As per the above quotes spring framework really saying developer don’t worry let’s do a party I will take care of everything. 

If you have hit this article that means you are familiar with Visual Studio code editor. You can download visual studio code if you haven’t by using the below link:


Configure the Spring boot with Visual Studio Code

After installation of vs code editor on your local system. Now we have considered below points to configure Spring boot with VS code.

I will assume you have done below configurations

  1. VS code installation.
  2. Java extension for VS Code.
  3. Kotlin extension if you want to develop a spring boot app using kotlin.

If above everything is done then go and open VS Code and go to extension and search for “spring”. You will able to something like the below image in your vscode editor.

Click and install “Spring Boot Extension Pack” Once the installation is done reload the VS code.

Spring Boot Extension Pack is acollection of extensions for developing and deploying Spring Boot Application.

  1. Spring boot tools.
  2. Spring Initializr Java Support.
  3. Spring Boot Dashboard.

Spring Boot Tools:

VSCode extension and Language Server providing support for working with Spring Boot application.properties, application.yml and .java files.

Spring Initializr Java Support:

Spring Initializr is a lightweight extension to quickly generate a Spring Boot project in Visual Studio Code (VS Code). It helps you to customize your projects with configurations and manage Spring Boot dependencies.

Spring Boot Dashboard:

Spring Boot Dashboard is a lightweight extension in Visual Studio Code (VS Code). With an explorer in the side bar, you can view and manage all available Spring Boot projects in your workspace. It also supports the features to quickly start, stop or debug a Spring Boot project.

Feature List

  • View Spring Boot apps in workspace
  • Start / Stop a Spring Boot app
  • Debug a Spring Boot app
  • Open a Spring Boot app in the browser
  • Generate a Maven/Gradle Spring Boot project
  • Customize configurations for a new project (language, group id, artifact id, boot version, and dependencies)
  • Search for dependencies
  • Quickstart with last settings
  • Edit Spring Boot dependencies of an existing Spring Boot project

Extention pack contains:

  1. IDE Java tooling for developing and troubleshooting Spring Boot applications.
  2. It provides support for editing Cloud Foundry deployment manifest .yml files for Spring Boot application deployment.
  3. The Concourse CI Pipeline Editor provides support for setting up Concourse build pipeline for the Spring Boot application.
  4. It provides support for generating quickstart Spring Boot Java projects with Spring Initiailizr API.
  5. It provides an explorer in the sidebar where you can view all of a workspace’s spring boot projects conveniently in one place.

This is it for now up to installation.

Want to create an application using vscode, check the below video. 

Spring Boot in VS Code

Use of spring initializer 

  • Launch VS Code
  • Press Ctrl + Shift + P to open the command palette.
  • Type Spring Initializr to start generating a Maven or Gradle project.
  • Follow the wizard.
  • Right-click inside the pom.xml file and choose Edit starters for dependency refactoring. (Gradle project is not supported yet, PR is welcome for it.)

Shortcuts may change based on the Operating System.

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Configuration as a Service: Spring Cloud Config – using kotlin.

Developing a microservice architecture with Java and Spring Boot is quite popular these days. In microservice architecture we hundreds of services and managing services for each service and for each profile which is a quite tedious task. In this article, we will demonstrate the Spring cloud config server using kotlin. 

Spring Boot provided a much-needed spark to the Spring projects.

Spring cloud-config provides a server and client-side support for externalizedconfiguration in a distributed system. With the Config Server, you have a central place to manage external properties for applications across all environments.

From the above diagram, you can easily predict that in distributed systems managing configuration as a central service is a bit tedious task and spring cloud config provide client, server architecture mechanism to manage the configuration easily. 

Let us go to the https://start.spring.io/

When we do any changes in any service we have to restart the services to apply the changes.

Let us create one git repo to manage our configuration and to achieve this we are creating one git repo.

So we will create “springbootclient” as one small spring boot microservice to take the username and that will read username from spring cloud config central configuration server system i.e git here.

We have created three different properties files for each of our different environments. 

  1. springbootclient.properties
  2. springbootclient-dev.properties
  3. springbootclient-prod.properties


Here is our spring cloud config properties are available, you can clone or use directly this repository too.

Now as we have created spring config server application using spring starter let us download and import that project in your favorite IDE or editor. git repo here we used to store our configuration and spring cloud config server application is to serve those properties to the client.

Basically git is datastore, spring cloud config server is server application and there are multiple microservices are the clients which needs configurations.

Now our git as datastore is ready. In this repository, we have created one sample client application and the name of that app is springbootclient. In the future microservice article we will utilize the same spring cloud config as a configuration server.

Let us go and check the code base for the client app.

This is the sample application.properties file:


Sample Code for SpringCloudConfigServerexApplication.kt

import org.springframework.boot.autoconfigure.SpringBootApplication
import org.springframework.boot.runApplication
import org.springframework.cloud.config.server.EnableConfigServer

class SpringCloudConfigServerexApplication

fun main(args: Array<String>) {

Now run and up the spring cloud-config server and check the below URL:


Spring Boot Client App:

Let us create one small microservice which will read configuration from spring cloud config server and serve that property value over REST end point.

Go to the https://start.spring.io/ and create spring boot client microservice using kotlin.

Sample POM.xml dependencies.


Now check the SpringCloudClientAppApplication.kt code

import org.springframework.boot.autoconfigure.SpringBootApplication
import org.springframework.boot.runApplication

class SpringCloudClientAppApplication

fun main(args: Array<String>) {

Now create one sample REST controller which is serving REST request. We want to check ” /whoami” this endpoint is returning which is the user based on active profile dev, prod, etc.


import org.springframework.beans.factory.annotation.Value
import org.springframework.web.bind.annotation.GetMapping
import org.springframework.web.bind.annotation.RestController

class UserController {

    var username="Test"
//get request serving
    fun whoami() = "I am a  "+ username


Create a bootstrap.properties file where we will specify the spring cloud config server details, which is a git branch and what is active profile dev, local, prod, etc.


All properties are self exclamatory, what is the use of which one.

Once you hit this URL http://localhost:9080/whoami

Output:- I am a DevUser

Github source link:

Config Server: https://github.com/maheshwarLigade/cloud-common-config-server

Codebase: https://github.com/maheshwarLigade/spring-cloud-config-kotlin-ex

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