Introduction

In this guide, we'll walk through the creation of a simple yet comprehensive microservices system using Spring Boot. We will cover the basics of microservices, setting up the required environment, and implementing two microservices: OrderService and InventoryService. Additionally, we'll integrate service discovery using Eureka and an API Gateway to manage routing between the services.

What is a Microservice?

Microservices are a software architecture style where an application is built as a collection of small, independent services that work together. Each service is self-contained and communicates with others through well-defined APIs, making the system more flexible, scalable, and easier to manage.

System Architecture

The architecture of our system will consist of two microservices: OrderService and InventoryService. The OrderService will use a relational database (MySQL) to store order details, while the InventoryService will use a NoSQL database (MongoDB) for managing inventory data. We'll also implement service discovery with Eureka and use an API Gateway for routing requests.

Project Setup

Before we begin, ensure you have the following tools installed:

• IDE: IntelliJ IDEA (preferred) or Eclipse
• JDK: Version 17 or later
• Build Tool: Maven
• Databases: MySQL and MongoDB

Microservice 1: Order Service

Step 1: Initialize the Project

1. Go to Spring Initializr.
2. Fill in the project details:
   • Project: Maven Project
   • Language: Java
   • Spring Boot: 2.5.7 (or a compatible version)
   • Group: com.ordersystem
   • Artifact: order-service
   • Name: order-service
   • Package name: com.ordersystem.orderservice
   • Packaging: Jar
   • Java: 17
3. Add the following dependencies:
   • Spring Web
   • Spring Data JPA
   • MySQL Driver
   • Lombok
4. Click Generate to download the project. Extract the downloaded zip file and open it in your IDE.

Step 2: Configure the Application

Open the application.properties file in src/main/resources and add the following configuration:

spring.datasource.url=jdbc:mysql://localhost:3306/orderservice
spring.datasource.username=root
spring.datasource.password=yourpassword
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
spring.jpa.hibernate.ddl-auto=update
spring.jpa.show-sql=true
spring.jpa.properties.hibernate.dialect=org.hibernate.dialect.MySQL8Dialect
server.port=8081

Step 3: Implement the Model

Create the Order entity class in src/main/java/com/ordersystem/orderservice/model/Order.java:

package com.ordersystem.orderservice.model;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

import javax.persistence.*;

@Data
@AllArgsConstructor
@NoArgsConstructor
@Entity
@Table(name = "orders")
public class Order {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String product;
    private int quantity;
    private double price;
}

Step 4: Create the Repository

Create the OrderRepository interface in src/main/java/com/ordersystem/orderservice/repository/OrderRepository.java:

package com.ordersystem.orderservice.repository;

import com.ordersystem.orderservice.model.Order;
import org.springframework.data.jpa.repository.JpaRepository;

public interface OrderRepository extends JpaRepository {
}

Step 5: Implement the Service

Create the OrderService class in src/main/java/com/ordersystem/orderservice/service/OrderService.java:

package com.ordersystem.orderservice.service;

import com.ordersystem.orderservice.model.Order;
import com.ordersystem.orderservice.repository.OrderRepository;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import java.util.List;

@Service
public class OrderService {
    @Autowired
    private OrderRepository orderRepository;

    public List getAllOrders() {
        return orderRepository.findAll();
    }

    public Order getOrderById(Long id) {
        return orderRepository.findById(id).orElse(null);
    }

    public Order createOrder(Order order) {
        return orderRepository.save(order);
    }

    public void deleteOrder(Long id) {
        orderRepository.deleteById(id);
    }
}

Step 6: Create the Controller

Create the OrderController class in src/main/java/com/ordersystem/orderservice/controller/OrderController.java:

package com.ordersystem.orderservice.controller;

import com.ordersystem.orderservice.model.Order;
import com.ordersystem.orderservice.service.OrderService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.*;

import java.util.List;

@RestController
@RequestMapping("/api/orders")
public class OrderController {
    @Autowired
    private OrderService orderService;

    @GetMapping
    public List getAllOrders() {
        return orderService.getAllOrders();
    }

    @GetMapping("/{id}")
    public Order getOrderById(@PathVariable Long id) {
        return orderService.getOrderById(id);
    }

    @PostMapping
    public Order createOrder(@RequestBody Order order) {
        return orderService.createOrder(order);
    }

    @DeleteMapping("/{id}")
    public void deleteOrder(@PathVariable Long id) {
        orderService.deleteOrder(id);
    }
}

Microservice 2: Inventory Service

Step 1: Initialize the Project

1. Go to Spring Initializr.
2. Fill in the project details:
   • Project: Maven Project
   • Language: Java
   • Spring Boot: 2.5.7 (or a compatible version)
   • Group: com.ordersystem
   • Artifact: inventory-service
   • Name: inventory-service
   • Package name: com.ordersystem.inventoryservice
   • Packaging: Jar
   • Java: 17
3. Add the following dependencies:
   • Spring Web
   • Spring Data MongoDB
   • Lombok
4. Click Generate to download the project. Extract the downloaded zip file and open it in your IDE.

Step 2: Configure the Application

Open the application.properties file in src/main/resources and add the following configuration:

spring.data.mongodb.uri=mongodb://localhost:27017/inventoryservice
server.port=8082

Step 3: Implement the Model

Create the InventoryItem entity class in src/main/java/com/ordersystem/inventoryservice/model/InventoryItem.java:

package com.ordersystem.inventoryservice.model;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import org.springframework.data.annotation.Id;
import org.springframework.data.mongodb.core.mapping.Document;

@Data
@AllArgsConstructor
@NoArgsConstructor
@Document(collection = "inventory")
public class InventoryItem {
    @Id
    private String id;
    private String product;
    private int quantity;
}

Step 4: Create the Repository

Create the InventoryRepository interface in src/main/java/com/ordersystem/inventoryservice/repository/InventoryRepository.java:

package com.ordersystem.inventoryservice.repository;

import com.ordersystem.inventoryservice.model.InventoryItem;
import org.springframework.data.mongodb.repository.MongoRepository;

public interface InventoryRepository extends MongoRepository {
}

Step 5: Implement the Service

Create the InventoryService class in src/main/java/com/ordersystem/inventoryservice/service/InventoryService.java:

package com.ordersystem.inventoryservice.service;

import com.ordersystem.inventoryservice.model.InventoryItem;
import com.ordersystem.inventoryservice.repository.InventoryRepository;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import java.util.List;

@Service
public class InventoryService {
    @Autowired
    private InventoryRepository inventoryRepository;

    public List getAllItems() {
        return inventoryRepository.findAll();
    }

    public InventoryItem getItemById(String id) {
        return inventoryRepository.findById(id).orElse(null);
    }

    public InventoryItem createItem(InventoryItem item) {
        return inventoryRepository.save(item);
    }

    public void deleteItem(String id) {
        inventoryRepository.deleteById(id);
    }
}

Step 6: Create the Controller

Create the InventoryController class in src/main/java/com/ordersystem/inventoryservice/controller/InventoryController.java:

package com.ordersystem.inventoryservice.controller;

import com.ordersystem.inventoryservice.model.InventoryItem;
import com.ordersystem.inventoryservice.service.InventoryService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.*;

import java.util.List;

@RestController
@RequestMapping("/api/inventory")
public class InventoryController {
    @Autowired
    private InventoryService inventoryService;

    @GetMapping
    public List getAllItems() {
        return inventoryService.getAllItems();
    }

    @GetMapping("/{id}")
    public InventoryItem getItemById(@PathVariable String id) {
        return inventoryService.getItemById(id);
    }

    @PostMapping
    public InventoryItem createItem(@RequestBody InventoryItem item) {
        return inventoryService.createItem(item);
    }

    @DeleteMapping("/{id}")
    public void deleteItem(@PathVariable String id) {
        inventoryService.delete

Item(id);
    }
}

Service Discovery with Eureka

Step 1: Initialize the Eureka Server

1. Go to Spring Initializr.
2. Fill in the project details:
   • Project: Maven Project
   • Language: Java
   • Spring Boot: 2.5.7 (or a compatible version)
   • Group: com.ordersystem
   • Artifact: eureka-server
   • Name: eureka-server
   • Package name: com.ordersystem.eurekaserver
   • Packaging: Jar
   • Java: 17
3. Add the Eureka Server dependency.
4. Click Generate to download the project. Extract the downloaded zip file and open it in your IDE.

Step 2: Configure the Eureka Server

Open the application.properties file in src/main/resources and add the following configuration:

server.port=8761
eureka.client.register-with-eureka=false
eureka.client.fetch-registry=false

Step 3: Enable Eureka Server

Annotate the main application class in src/main/java/com/ordersystem/eurekaserver/EurekaServerApplication.java with @EnableEurekaServer:

package com.ordersystem.eurekaserver;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.netflix.eureka.server.EnableEurekaServer;

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

Integrate Services with Eureka

Add the Eureka client dependency to both OrderService and InventoryService:

    org.springframework.cloud
    spring-cloud-starter-netflix-eureka-client

Add Eureka client configuration to the application.properties files:

Order Service:

eureka.client.service-url.defaultZone=http://localhost:8761/eureka/
spring.application.name=order-service

Inventory Service:

eureka.client.service-url.defaultZone=http://localhost:8761/eureka/
spring.application.name=inventory-service

API Gateway

Step 1: Initialize the API Gateway

1. Go to Spring Initializr.
2. Fill in the project details:
   • Project: Maven Project
   • Language: Java
   • Spring Boot: 2.5.7 (or a compatible version)
   • Group: com.ordersystem
   • Artifact: api-gateway
   • Name: api-gateway
   • Package name: com.ordersystem.apigateway
   • Packaging: Jar
   • Java: 17
3. Add the Gateway and Eureka Discovery Client dependencies.
4. Click Generate to download the project. Extract the downloaded zip file and open it in your IDE.

Step 2: Configure the API Gateway

Open the application.yml file in src/main/resources and add the following configuration:

server:
  port: 8080

spring:
  application:
    name: api-gateway
  cloud:
    gateway:
      routes:
        - id: order-service
          uri: lb://order-service
          predicates:
            - Path=/api/orders/**
        - id: inventory-service
          uri: lb://inventory-service
          predicates:
            - Path=/api/inventory/**

eureka:
  client:
    service-url:
      defaultZone: http://localhost:8761/eureka/

Step 3: Enable Discovery Client

Annotate the main application class in src/main/java/com/ordersystem/apigateway/ApiGatewayApplication.java with @EnableDiscoveryClient:

package com.ordersystem.apigateway;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;

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

Testing the Microservices

1. Start Eureka Server: Run the Eureka Server application.
2. Start Order Service: Run the Order Service application.
3. Start Inventory Service: Run the Inventory Service application.
4. Start API Gateway: Run the API Gateway application.

Use Postman or any other API client to test the endpoints through the API Gateway:

• Create Order: POST http://localhost:8080/api/orders
• Get Orders: GET http://localhost:8080/api/orders
• Create Inventory Item: POST http://localhost:8080/api/inventory
• Get Inventory Items: GET http://localhost:8080/api/inventory

Conclusion

In this guide, we've built a simple microservices system using Spring Boot. We created two microservices (OrderService and InventoryService), integrated service discovery with Eureka, and set up an API Gateway for routing requests. This architecture allows for scalable and maintainable microservices that can be easily extended in the future.