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Employee Management System

A backend-only Employee Management System built using Spring Web MVC and an H2 embedded database. This project focuses on core Spring MVC concepts, layered architecture, validation, exception handling, and clean API design.

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🚀 Key Features

• REST-style employee management APIs
• Centralized global exception handling
• Custom domain-specific exceptions
• Input validation using annotations
• Custom validation annotation for employee roles
• Partial updates using PATCH
• Reflection-based field updates
• Proper HTTP status codes using ResponseEntity
• Clean separation of controller, service, and persistence layers
• In-memory H2 database for easy setup

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🛠 Tech Stack

• Java
• Spring Web MVC
• H2 Embedded Database
• Maven
• Apache Tomcat
• Lombok
• ModelMapper

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🔁 API Endpoints

Method	Endpoint	Description
POST	/employees	Create a new employee
GET	/allemployees	Retrieve all employees
GET	/employees/{id}	Retrieve employee by ID
PUT	/employees/{id}	Update full employee details
PATCH	/employees/{id}	Partially update employee fields
DELETE	/employees/{id}	Delete an employee

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🧠 Backend Concepts Implemented

Global Exception Handling

• Centralized error handling using @ControllerAdvice
• Custom ResourceNotFoundException
• Clean, consistent error responses

Input Validation

• Standard validation annotations (@NotNull, @Size, etc.)
• Custom @EmployeeRole annotation for domain-specific validation
• Validation errors mapped to meaningful HTTP responses

Partial Updates (PATCH)

• Supports updating only selected fields
• Uses Java Reflection to dynamically update fields
• Prevents overwriting unchanged data

Response Customization

• Uses ResponseEntity to return:

  • Proper HTTP status codes
  • Clear success and error messages

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🧱 Architecture

The project follows a layered Spring MVC architecture:

• Controller Layer

  • Handles HTTP requests
  • Defines endpoint mappings
  • Delegates logic to services

• Service Layer

  • Contains business logic
  • Handles validation and transformations
  • Coordinates between controller and persistence layers

• Persistence Layer

  • Responsible for database interactions
  • Encapsulates data access logic

• DTO & Model Layer

  • DTOs for API contracts
  • Models represent domain entities
  • Mapping handled using ModelMapper

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🗄 Database

• H2 In-Memory Database
• Automatically configured at runtime
• No external database required
• Data resets on application restart

H2 Console

http://localhost:8080/h2-console
JDBC URL: jdbc:h2:mem:testdb
Username: sa
Password:

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⚙️ Running the Application

Prerequisites

• Java 8+
• Maven

Steps

git clone https://github.com/your-username/employee-management-system.git
cd employee-management-system
mvn clean install

Deploy the generated WAR file on Tomcat or run directly from your IDE.

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📂 Project Structure

src/main/java
 └── com.example.employeemanagement
     ├── controller
     ├── service
     ├── repository
     ├── exception
     ├── validation
     ├── dto
     └── model

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🎯 Learning Objectives

• Master Spring Web MVC fundamentals
• Understand request lifecycle and mappings
• Design clean REST-style APIs
• Implement validation and error handling correctly
• Use reflection safely for partial updates
• Build backend systems without heavy abstractions

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🔮 Future Enhancements

• Pagination and sorting
• API documentation (Swagger / OpenAPI)
• Logging and monitoring
• Authentication and authorization
• Migration to an external database

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