ProductServiceSpring

A Spring Boot REST API for managing a product catalog, built with a dual-datasource strategy — a live MySQL database and an external FakeStore API proxy.

The project also includes a hands-on demonstration of all four JPA inheritance mapping strategies.

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Tech Stack

Layer	Technology
Language	Java 17
Framework	Spring Boot 3.2.3
Persistence	Spring Data JPA + Hibernate
Database	MySQL 8
External API	FakeStore API via RestTemplate
Boilerplate Reduction	Lombok
Build Tool	Maven

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Architecture Overview

The service exposes a single REST controller (ProductController) backed by a swappable service layer via Spring's @Qualifier annotation.

Client Request
     │
     ▼
ProductController  (/products)
     │
     ├─── @Qualifier("SelfProductService")
     │         └── ProductServiceImpl  ──► ProductRepo (MySQL JPA)
     │                                 └── CategoryRepo (MySQL JPA)
     │
     └─── @Qualifier("FakeProductService")
               └── FakeStoreProductServiceImpl ──► FakeStoreClient (RestTemplate)
                                                        └── fakestoreapi.com

Switch between the two implementations by changing the @Qualifier in ProductController.

No other code needs to change — this is the Strategy Pattern in action.

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REST API Endpoints

Base path: /products

Method	Endpoint	Description
GET	/products/{id}	Get a product by ID
GET	/products	Get all products
POST	/products	Create a new product
PUT	/products/{id}	Update an existing product
DELETE	/products/{id}	Delete a product by ID

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Sample Request — Create Product

POST /products

{
  "title": "Wireless Headphones",
  "description": "Over-ear noise cancelling",
  "price": 2999,
  "category": {
    "name": "Electronics"
  }
}

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Sample Error Response

HTTP 404

{
  "message": "Product not found with id: 42",
  "status": "failure"
}

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Project Structure

src/main/java/com/example/productservicecp/
│
├── ProductServiceJanBatchApplication.java
│
├── controllers/
│   ├── ProductController.java
│   └── advices/
│       └── ProductControllerAdvice.java
│
├── services/
│   ├── ProductService.java
│   ├── ProductServiceImpl.java
│   ├── FakeStoreProductServiceImpl.java
│   └── FakeproductServiceObjectMapper.java
│
├── thirdpartyclients/
│   └── FakeStoreClient.java
│
├── models/
│   ├── BaseModel.java
│   ├── Product.java
│   └── Category.java
│
├── repository/
│   ├── ProductRepo.java
│   └── CategoryRepo.java
│
├── dtos/
│   ├── FakeStoreProductDto.java
│   └── ExceptionDto.java
│
├── exceptions/
│   └── ProductNotFoundException.java
│
└── inheritancedemo/
    ├── singletable/
    ├── tableperclass/
    ├── joinedtable/
    └── mappedsuper/

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Data Model

Product

Field	Type	Notes
id	Long	Auto-generated primary key
title	String	Product name
description	String	Product description
price	Long	Price in smallest currency unit
category	Category	@ManyToOne relationship

Category

Field	Type	Notes
id	Long	Auto-generated
name	String	Category name

Key Behaviour

When adding or updating a product, the service checks whether the category already exists by name using:

CategoryRepo.findByName()

If it exists, the existing category is reused. Otherwise, a new category is created.

This prevents duplicate category rows.

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Key Design Patterns

Strategy Pattern

ProductService interface with two implementations:

• ProductServiceImpl
• FakeStoreProductServiceImpl

The controller depends on the interface, not the concrete class.

Implementation is swapped via @Qualifier.

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DTO Pattern

FakeStoreProductDto decouples the internal Product domain model from the external API contract.

Conversion happens inside FakeStoreProductServiceImpl.

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Global Exception Handling

ProductControllerAdvice uses @RestControllerAdvice scoped to ProductController.

It catches ProductNotFoundException and returns structured JSON error responses.

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Third-Party Client Abstraction

FakeStoreClient encapsulates all RestTemplate logic for external API interaction.

The service layer never directly interacts with RestTemplate.

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JPA Inheritance Demo

The inheritancedemo package demonstrates all four Hibernate inheritance strategies using a User → Mentor / Student hierarchy.

Strategy	Tables Created	Trade-off
SINGLE_TABLE	One table with discriminator column	Fast reads, nullable columns
TABLE_PER_CLASS	One table per concrete class	No joins, duplicated schema
JOINED	Parent + child tables	Normalized, slower joins
MAPPED_SUPERCLASS	Only child tables	No polymorphic parent queries

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Setup & Running Locally

Prerequisites

• Java 17+
• Maven 3.8+
• MySQL 8

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1. Configure Database

CREATE DATABASE jan24productservice;

CREATE USER 'jan24productservice'@'localhost'
IDENTIFIED BY 'your_password';

GRANT ALL PRIVILEGES
ON jan24productservice.*
TO 'jan24productservice'@'localhost';

Update:

src/main/resources/application.properties

spring.datasource.password=your_password

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2. Build & Run

./mvnw spring-boot:run

Application starts on:

http://localhost:8080

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3. Switch Between Datasources

In ProductController.java:

// Use local MySQL
@Qualifier("SelfProductService")

// Use FakeStore API
@Qualifier("FakeProductService")

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Configuration Reference

# FakeStore API
fakestore.api.url=https://fakestoreapi.com/products/{id}

# Database
spring.jpa.hibernate.ddl-auto=update
spring.datasource.url=jdbc:mysql://localhost:3306/jan24productservice
spring.datasource.username=jan24productservice
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver

# Hibernate
spring.jpa.show-sql=true
spring.jpa.properties.hibernate.dialect=org.hibernate.dialect.MySQL8Dialect

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What Is Not Implemented

• Elasticsearch
• Kafka
• Spring Cloud / Microservices
• Authentication / Authorization
• Pagination on GET /products
• Full implementation of getAllProducts()
• Full implementation of deleteProductById()

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License

MIT