Quick Microservice With Gradle Spring Boot Docker

A few years ago if you would have asked me to create a quick POC backend service with some rest APIs I would have just picked up NetBeans and created the REST APIs using jersey/glassfish (reference implementation of JSR 311 RESTful Web Services) from the UI itself. While the above is an example of creating REST APIs bottom-up from the Database layer, once can plug business logic by adding few more java classes or a service layer. Lately, I have been using Spring Boot a lot in production and it really makes the developer's life easy by not having to write a lot of boilerplate code. Annotations take care of Dependency injection, singleton, REST API mappings etc. It even has the embedded Jetty web server to run the service locally without really having to install a bulk of binary like Glassfish/Tomcat server and deploy them (comes integrated with Netbeans tough - one could right click and run the service). However, Spring Boot + Gradle makes the code ultraportable. All you need to do is check-out from the code repo and run Gradle/Spring Boot command to build or run. Even the testing tools can be easily added to gradle and both Unit and Integration test can be written. There are so may example of hello world with Spring Boot and Gradle on the internet, but I thought of keeping a copy of simple skeleton of service which I can use to bootstrap any app in future. Even better - dockerize the app and create an image out of it which can run anywhere irrespective of the host machine and its setup. Later we can also push it to a public container registry and use it in Minikube or Kubernetes in the cloud (probably in a separate post).

I assume one has installed Java and gradle (only needed for creating the project but the subsequent setup will be taken care by gradlew, the wrapper which can download gradle itself)

Code

To create a skeleton

  
     gradle init --type java-application 
  

Now add the spring boot dependencies in build.gragle.

  
   plugins {
   ...
       id 'com.gradle.build-scan' version '1.16'
       id 'org.springframework.boot' version '2.0.5.RELEASE'
  }
  

  
dependencies {
// This dependency is found on compile classpath of this component and consumers.
    implementation 'org.springframework.boot:spring-boot-dependencies:2.0.5.RELEASE'
    implementation 'org.springframework.boot:spring-boot-starter-web:2.0.5.RELEASE'
  

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class App {dle
    public static void main(String[] args) {
    SpringApplication.run(App.class, args);
    }
}

Now tell gradle (in build.gradle)which one is the main class

 bootJar {
     mainClassName = 'hello.App'
 }

The whole code can be checked out from

git clone https://github.com/neilghosh/simple-gradle-springboot-service

Build

Now one can build the jar with all the dependencies

./gradlew bootJar

the jar will be created in the ./build directory.

Run

Now we can run the app by either

./gradlew bootRun

or run the jar itself

java -jar build/libs/simple-gradle-springboot-service .jar

Dockerize

We can create the following simple Dockerfile to import the OpenJDK base image and copy the jar to an appropriiate directory and run command.

      FROM openjdk:8-jdk-alpine
      RUN mkdir -p /app/
      ADD    build/libs/simple-gradle-springboot-service.jar /app/app.jar
      ENTRYPOINT ["java", "-jar", "/app/app.jar"]

Build the docker image

docker build . -t gradle-spring-boot-app

Check the local image created

docker images

REPOSITORY TAG IMAGE ID CREATED SIZE
gradle-spring-boot-app latest 21572d4766d3 About an hour ago 124MB

And run the docker image exposing the port to host

docker run -p 8080:8080 gradle-spring-boot-app:latest

Profit

$ curl http://localhost:8080/
Hello Gradle!

Next, we will see how to push the local cached imaged to a docker registry and run in cloud or Minikube