🚀 Spring IOC, Beans & JPA — Product Catalog System

A complete, production‑style demonstration of Spring IOC, Beans, Dependency Injection, Spring MVC, Spring Data JPA, and Thymeleaf, wrapped into a functional Product Catalog Web Application.

This project showcases real‑world Spring Framework fundamentals with a clean architecture and fully working CRUD features.

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📌 Table of Contents

• Overview
• Features
• System Architecture
• Flow Diagram
• Tech Stack
• Project Structure
• Endpoints & Views
• Entity Model
• How to Run
• H2 Database Access
• Troubleshooting
• License

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📖 Overview

This Spring Boot + IOC + Beans powered application provides a simple yet powerful Product Catalog with full CRUD behavior through:

• Thymeleaf‑based UI
• Spring MVC controllers
• JPA repositories
• H2 in-memory DB
• IOC + DI-managed services

It is ideal for learning or demonstrating Spring Core concepts.

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🌟 Features

✔ Dependency Injection & IoC

Services and controllers are wired automatically using Spring Beans.

✔ Add Products

Fill out a form and store product data in H2 DB via JPA.

✔ Display Products

See all products in a table with sorting and clean UI.

✔ Filter by Category

Uses repository-level custom query.

✔ Thymeleaf UI

Server-side rendered dynamic HTML pages.

✔ In-Memory H2 Database

Zero configuration, auto‑created schema.

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🏛 System Architecture

graph TD
    A[User Browser] --> B[Spring MVC Controller]
    B --> C[Service Layer]
    C --> D[Repository Layer]
    D --> E[(H2 Database)]
    B --> F[Thymeleaf Templates]

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🔄 Flow Diagram (Page → Controller → Service → DB)

sequenceDiagram
    participant U as User
    participant C as Controller
    participant S as Service
    participant R as JPA Repository
    participant DB as H2 DB

    U->>C: GET /
    C->>U: index.html

    U->>C: GET /add-product
    C->>U: addproduct.html

    U->>C: POST /add-product
    C->>S: saveProduct(product)
    S->>R: save(product)
    R->>DB: INSERT
    C->>U: redirect:/ 

    U->>C: GET /display-products?category=...
    C->>S: getProducts(...)
    S->>R: findByCategory() OR findAll()
    R->>DB: SELECT
    C->>U: displayproduct.html

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🧰 Tech Stack

Component	Technology
Language	Java 17
Framework	Spring Boot, Spring Core
DI / IoC	Spring Beans
Persistence	Spring Data JPA (Hibernate)
Database	H2 In‑Memory
Template Engine	Thymeleaf
Build Tool	Maven

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📂 Project Structure

src/
 ├── main/
 │   ├── java/com/SpringIOC/demo/
 │   │     ├── controller/
 │   │     │    └── ProductController.java
 │   │     ├── service/
 │   │     │    └── ProductService.java
 │   │     ├── repository/
 │   │     │    └── ProductRepository.java
 │   │     ├── entity/
 │   │     │    └── Product.java
 │   │     └── SpringIoc1Application.java
 │   │
 │   └── resources/
 │         ├── templates/
 │         │     ├── index.html
 │         │     ├── addproduct.html
 │         │     └── displayproduct.html
 │         ├── application.properties
 │         └── static/
 │
 └── test/
       └── SpringIoc1ApplicationTests.java

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🔗 Endpoints & Views

URL	Method	Description	View
/	GET	Homepage	index
/add-product	GET	Show product form	addproduct
/add-product	POST	Save new product	redirect:/
/display-products	GET	Display all or filtered	displayproduct

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🗄 Entity Model

Product.java

id       (Long, Auto-generated)
name     (String)
price    (Double)
category (String)

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▶️ How to Run

1. Clone the Repo

git clone <REPO_URL>
cd SpringIOC

2. Build the Project

mvn clean install

3. Run

mvn spring-boot:run

4. Access in Browser

http://localhost:8080/

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🗃 H2 Database Access

Visit:

http://localhost:8080/h2-console

Use:

Key	Value
JDBC URL	jdbc:h2:mem:productdb;DB_CLOSE_ON_EXIT=FALSE
Username	sa
Password	(empty)

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🛠 Troubleshooting

⚠ Whitelabel Error

Caused by template naming mismatch.
Ensure:

return "addproduct";  → templates/addproduct.html
return "displayproduct"; → templates/displayproduct.html

⚠ H2 Shutdown Error

Fixed by:

spring.datasource.url=jdbc:h2:mem:productdb;DB_CLOSE_ON_EXIT=FALSE

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📄 License

MIT License.

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