Java Spring Boot CRUD Demo Application

Overview

This project is a beginner-friendly Java Spring Boot application demonstrating basic CRUD (Create, Read, Update, Delete) operations using RESTful APIs, JPA, and H2 in-memory database. It is designed to help you learn the fundamentals of building web applications with Spring Boot.

Features

• RESTful API endpoints for managing Employee data
• CRUD operations: Create, Read, Update, Delete
• Uses DTOs, Entities, Repositories, Services, and Controllers
• ModelMapper for object mapping
• H2 in-memory database for easy setup
• Maven build system

Technologies Used

• Java 17+
• Spring Boot 3+
• Spring Data JPA
• H2 Database
• ModelMapper
• Maven

Prerequisites

• Java JDK 17 or higher
• Maven
• IDE (IntelliJ IDEA, Eclipse, VS Code, etc.)

Getting Started

1. Clone the repository:

   git clone https://github.com/your-username/demo-java-app-crud.git
   

2. Navigate to the project directory:

   cd demo-java-app-crud/demo
   

3. Build the project:

   mvn clean install
   

4. Run the application:

   mvn spring-boot:run
   

5. Access H2 Console:
   • Visit http://localhost:8080/h2-console
   • JDBC URL: jdbc:h2:mem:testdb

Project Structure

demo/
├── src/main/java/com/demo1/deepjha/demo/
│   ├── DemoApplication.java         # Main Spring Boot application
│   ├── entities/EmployeeEntity.java # Entity class (maps to DB)
│   ├── dto/EmployeeDTO.java         # Data Transfer Object
│   ├── repositories/EmployeeRepository.java # JPA Repository
│   ├── services/EmployeeService.java # Business logic
│   ├── controllers/EmployeeController.java # REST API endpoints
│   └── configuration/AppConfig.java # ModelMapper bean config
├── src/main/resources/
│   └── application.properties       # DB and app config
├── pom.xml                         # Maven dependencies

How CRUD Works

• Create: POST /employees - Add a new employee
• Read: GET /employees - Get all employees
• Update: PUT /employees/{id} - Update employee by ID
• Delete: DELETE /employees/{id} - Delete employee by ID

Sample Request (Create Employee)

{
  "name": "John Doe",
  "email": "john.doe@example.com",
  "phone": "1234567890",
  "dateOfJoining": "2023-01-01",
  "isActive": true
}

Key Concepts Explained

Entity

Represents a table in the database. Example: EmployeeEntity.java defines fields like id, name, email, etc.

DTO (Data Transfer Object)

Used to transfer data between layers (e.g., from client to server). Keeps internal model safe and flexible.

Repository

Interface for database operations. Extends JpaRepository to provide CRUD methods.

Service

Contains business logic. Calls repository methods and handles data transformation.

Controller

Defines REST API endpoints. Receives HTTP requests and returns responses.

ModelMapper

Library for mapping between DTOs and Entities. Reduces manual conversion code.

Example Usage

ModelMapper modelMapper = new ModelMapper();
EmployeeEntity entity = modelMapper.map(employeeDTO, EmployeeEntity.class);

Database Configuration (H2)

• H2 is an in-memory database, so data is lost when the app stops.
• Configured in application.properties:

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

Common Errors & Troubleshooting

• Dialect not set: Ensure spring.jpa.database-platform is set in application.properties.
• H2 Console not accessible: Check spring.h2.console.enabled=true.
• Data not persisting: H2 is in-memory; use a file-based DB for persistence.

Useful Resources

• Spring Boot Documentation
• Spring Data JPA Guide
• ModelMapper Documentation
• H2 Database Guide
• Baeldung Spring Boot Tutorials

Next Steps for Beginners

• Try adding new fields to Employee
• Implement validation
• Switch to a persistent database (e.g., MySQL)
• Add unit and integration tests
• Explore authentication and security

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Happy coding! If you have questions, check the resources above or open an issue.