Spring Boot Project Setup

 

1. Spring Boot Project Setup (using Spring Initializer)

Go to 👉 https://start.spring.io and generate a project with:

• Project: Maven

• Language: Java

• Spring Boot: 3.2 (or latest stable)

• Dependencies:

  • Spring Web

  • Spring Data JPA

  • H2 Database

  • Spring Boot Actuator

Click “Generate”, then unzip and open it in IntelliJ IDEA, VS Code, or Eclipse.

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📁 2. Project Structure Breakdown

customer-service/
├── src/main/java/com/example/customer
│   ├── CustomerServiceApplication.java   <-- Main app class
│   ├── controller/CustomerController.java <-- REST API logic
│   ├── model/Customer.java               <-- Data structure (Entity)
│   └── repository/CustomerRepository.java <-- DB operations
├── src/main/resources
│   └── application.yml                   <-- Configuration file
├── pom.xml                               <-- Maven build file

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✅ 3. Step-by-Step File Explanation

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📌 CustomerServiceApplication.java

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

🔹 Explanation:

• @SpringBootApplication = Combines 3 annotations:

  • @Configuration (declares beans)

  • @EnableAutoConfiguration (auto sets up Spring features)

  • @ComponentScan (scans your code for components like @Controller)

• main() = the entry point. Runs the app like a regular Java program.

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📌 Customer.java (inside model/)

@Entity
public class Customer {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;
    private String email;

    // Getters & setters
}

🔹 Explanation:

• This is a Java class (POJO) that represents a table in the database.

• @Entity tells Spring it's a database table.

• @Id = primary key, @GeneratedValue = auto-increment.

• When the app runs, Spring Boot creates a table named customer in the H2 DB.

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📌 CustomerRepository.java (inside repository/)

public interface CustomerRepository extends JpaRepository<Customer, Long> {}

🔹 Explanation:

• This is an interface — no code inside, yet it works!

• JpaRepository provides built-in methods like:

  • findAll()

  • save()

  • deleteById()

  • findById()

• Spring will generate the implementation automatically.

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📌 CustomerController.java (inside controller/)

@RestController
@RequestMapping("/api/customers")
public class CustomerController {

    @Autowired
    private CustomerRepository repository;

    @GetMapping
    public List<Customer> getAll() {
        return repository.findAll();
    }

    @PostMapping
    public Customer create(@RequestBody Customer customer) {
        return repository.save(customer);
    }
}

🔹 Explanation:

• @RestController = this class handles HTTP requests and returns data.

• @RequestMapping("/api/customers") = base path for all endpoints.

• @Autowired = Spring injects the repository automatically.

• @GetMapping = handles GET /api/customers (return all customers).

• @PostMapping = handles POST /api/customers (create a new customer).

• @RequestBody = converts incoming JSON to a Customer object.

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📌 application.yml

server:
  port: 8080

spring:
  datasource:
    url: jdbc:h2:mem:testdb
    driverClassName: org.h2.Driver
    username: sa
    password:
  jpa:
    hibernate:
      ddl-auto: update
    show-sql: true

management:
  endpoints:
    web:
      exposure:
        include: "*"

🔹 Explanation:

• Tells Spring Boot to:

  • Use port 8080

  • Use in-memory H2 DB

  • Automatically update the schema from entities

  • Expose health, metrics, and other actuator endpoints

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▶️ 4. Running the App

1. Run CustomerServiceApplication.java (as Java Application)

2. Test in browser or with curl/Postman:

curl http://localhost:8080/api/customers

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🐳 5. Dockerizing the App

Step-by-step:

🐘 Build the project

mvn clean package

This creates a file like target/customer-service-0.0.1-SNAPSHOT.jar.

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🐳 Dockerfile

FROM openjdk:17-jdk-slim
WORKDIR /app
COPY target/*.jar app.jar
ENTRYPOINT ["java", "-jar", "app.jar"]

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🛠 Build and Run Docker

docker build -t customer-service .
docker run -p 8080:8080 customer-service

Now your app is running in a container!

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🚀 6. CI/CD with GitHub Actions

Here’s a simple GitHub Actions pipeline:

.github/workflows/build.yml

name: Build Spring Boot App

on:
  push:
    branches: [main]

jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v3
      - uses: actions/setup-java@v3
        with:
          java-version: '17'
          distribution: 'temurin'

      - name: Build with Maven
        run: mvn clean package

      - name: Build Docker image
        run: docker build -t my-customer-service .

      # Optionally, push to DockerHub or deploy to Kubernetes

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🛠️ 7. Debugging Tips

🔧 Common errors and how to fix:

Problem	Symptom	Fix
Port in use	App fails to start	Change server.port
H2 DB error	Cannot connect	Fix DB URL or check logs
NullPointer	Missing @Autowired	Add annotation
App not accessible in Docker	No port exposed	Use -p 8080:8080 in Docker run

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✅ Summary

Task	Tool
Build app	Spring Boot + Maven
Test locally	Curl/Postman
Deploy in container	Docker
Automate	GitHub Actions
Monitor health	Actuator /actuator/health
Debug	Logs, Postman, Spring DevTools