java-example-nag-jar

└──> source code for building jar application

📦 Simple Spring Boot Application (Java 21+)

This is a minimal Spring Boot application that:

• Uses Java 21+
• Runs on port 8085
• Can be built using Maven or Gradle
• Can be packaged into a Docker image
• Can be deployed to Kubernetes

---

📁 Project Structure

java-example-nag-jar/
 ├── src/main/java/com/example/demo/DemoApplication.java
 ├── src/main/resources/application.yml
 ├── pom.xml
 ├── build.gradle
 ├── settings.gradle
 ├── Dockerfile
 └── k8s-deployment.yaml

---

☕ Java Code

DemoApplication.java

package com.example.demo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@SpringBootApplication
@RestController
public class DemoApplication {

    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }

    @GetMapping("/")
    public String home() {
        return "Hello, Spring Boot is running on port 8085!";
    }
}

---

⚙️ application.yml

server:
  port: 8085

---

📦 pom.xml (Maven)

<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 http://www.m...">

    <modelVersion>4.0.0</modelVersion>

    <groupId>com.example</groupId>
    <artifactId>demo</artifactId>
    <version>java-example-demo-1.0.0</version>
    <name>demo</name>
    <description>Simple Spring Boot App</description>

    <properties>
        <java.version>21</java.version>
        <spring.boot.version>3.3.0</spring.boot.version>
    </properties>

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-dependencies</artifactId>
                <version>${spring.boot.version}</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <version>${spring.boot.version}</version>
            </plugin>
        </plugins>
    </build>

</project>

---

⚙️ build.gradle (Gradle)

plugins {
    id 'java'
    id 'org.springframework.boot' version '3.3.0'
    id 'io.spring.dependency-management' version '1.1.6'
}

group = 'com.example'
version = 'java-example-demo-1.0.0'

java {
    toolchain {
        languageVersion = JavaLanguageVersion.of(21)
    }
}

repositories {
    mavenCentral()
}

dependencies {
    implementation 'org.springframework.boot:spring-boot-starter-web'
}


tasks.named('test') {
    useJUnitPlatform()
}

settings.gradle

rootProject.name = 'demo'

---

🐳 Dockerfile

FROM eclipse-temurin:21-jdk

WORKDIR /app

COPY target/java-example-demo-1.0.0.jar app.jar

EXPOSE 8085

ENTRYPOINT ["java", "-jar", "app.jar"]

---

☸️ Kubernetes YAML

k8s-deployment.yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: spring-boot-app
spec:
  replicas: 1
  selector:
    matchLabels:
      app: spring-boot-app
  template:
    metadata:
      labels:
        app: spring-boot-app
    spec:
      containers:
        - name: spring-boot-container
          image: your-dockerhub-username/demo:latest
          ports:
            - containerPort: 8085
---
apiVersion: v1
kind: Service
metadata:
  name: spring-boot-service
spec:
  type: NodePort
  selector:
    app: spring-boot-app
  ports:
    - port: 80
      targetPort: 8085
      nodePort: 30007

---

🚀 How to Use

Build using Maven

mvn clean install

Run the JAR

java -jar target/java-example-demo-1.0.0.jar

Build using Gradle

gradle clean build

Run the JAR

java -jar build/libs/java-example-demo-1.0.0.jar

Build Docker Image

docker build -t your-dockerhub-username/demo:latest .

Deploy to Kubernetes

kubectl apply -f k8s-deployment.yaml

---

✅ Output

Open browser:

http://<server_IP>:8085

You should see:

Hello, Spring Boot is running on port 8085!

---