Whether you are developing a single microservice or a complex system, Spring Boot provides all the tools and frameworks needed to succeed.

Before we start, ensure you have the following prerequisites:

• Java Development Kit (JDK) 8 or higher
• Spring Boot installed via Maven or Gradle
• A preferred Integrated Development Environment (IDE) like IntelliJ IDEA, Eclipse, or VS Code
• Basic understanding of Java and RESTful APIs

Follow these steps to build your first microservice:

We will use Spring Initializr to generate the basic structure of our Spring Boot application:

1. Navigate to start.spring.io.
2. Choose Gradle or Maven as the project type and Java as the language.
3. Set the Group and Artifact IDs. For example:
   Group: com.example
   Artifact: product-service
4. Add dependencies: Spring Web, Spring Data JPA, and H2 Database.
5. Click Generate to download the project.

Extract the ZIP file and import the project into your IDE.

In a microservice, each service has a specific purpose. Let's create a Product service for managing product information. Define the following:

public class Product {
    private Long id;
    private String name;
    private double price;

    // Getters and Setters
}

Create a repository interface to manage database interactions:

import org.springframework.data.jpa.repository.JpaRepository;

public interface ProductRepository extends JpaRepository<Product, Long> {
}

Now, create a service layer to handle business logic:

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import java.util.List;

@Service
public class ProductService {

    @Autowired
    private ProductRepository repository;

    public List<Product> getAllProducts() {
        return repository.findAll();
    }

    public Product addProduct(Product product) {
        return repository.save(product);
    }
}

Expose the service through a REST controller:

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

import java.util.List;

@RestController
@RequestMapping("/products")
public class ProductController {

    @Autowired
    private ProductService productService;

    @GetMapping
    public List<Product> getAllProducts() {
        return productService.getAllProducts();
    }

    @PostMapping
    public Product addProduct(@RequestBody Product product) {
        return productService.addProduct(product);
    }
}

Spring Boot supports in-memory databases like H2 for quick development and testing. Add the following configuration in your application.properties file:

spring.datasource.url=jdbc:h2:mem:testdb
spring.datasource.driverClassName=org.h2.Driver
spring.datasource.username=sa
spring.datasource.password=password
spring.jpa.database-platform=org.hibernate.dialect.H2Dialect

To test the application:

1. Run the Spring Boot application using mvn spring-boot:run or ./gradlew bootRun.
2. Use tools like Postman or curl to interact with the endpoints:

curl --location --request POST 'http://localhost:8080/products' \
--header 'Content-Type: application/json' \
--data-raw '{ "name": "Laptop", "price": 999.99 }'

curl --location --request GET 'http://localhost:8080/products'

You will see the list of products returned by the service.

To package the application as a JAR, run:

mvn clean package

This will create a JAR file in the target directory, which you can run independently:

java -jar target/product-service-0.0.1-SNAPSHOT.jar

Congratulations! You have built your first microservice using Spring Boot. This microservice can now be expanded or integrated into a larger system. In subsequent articles, we will explore how to enhance microservices with advanced features like external configuration, communication between services, and security.