Employee Management System

A console-based Employee Management System built in Java with JDBC and MySQL. It uses a layered design (Main, Service, DAO, Database), validates all user input, and comes with JUnit and Mockito unit tests.

Features

• Add a new employee (first name, last name, department, salary, email)
• View all employees
• Find an employee by ID
• Update an employee's department, salary, email, or all three at once
• Delete an employee
• Input validation for names, department, salary, ID and email format
• Duplicate email detection, enforced by a UNIQUE constraint in the database
• Clear error messages using custom exceptions (InvalidInputException, EmployeeNotFoundException, DuplicateEmailException)

Tech Stack

• Java 21
• Maven
• JDBC with MySQL Connector/J
• MySQL
• JUnit 5 and Mockito for testing
• JaCoCo for test coverage

Project Structure

src/
├── main/java/
│   ├── Main.java                    Console menu
│   ├── dao/
│   │   ├── EmployeeDAO.java         DAO interface
│   │   └── EmployeeDAOImpl.java     JDBC implementation
│   ├── exception/
│   │   ├── DuplicateEmailException.java
│   │   ├── EmployeeNotFoundException.java
│   │   └── InvalidInputException.java
│   ├── model/
│   │   └── Employee.java            Employee data class
│   ├── service/
│   │   └── EmployeeService.java     Validation and business logic
│   └── util/
│       └── DBConnection.java        Reads db.properties, opens connections
└── test/java/
    ├── model/EmployeeTest.java
    └── service/EmployeeServiceTest.java
schema.sql                           Database and table creation
db.properties.example                Template for database credentials
pom.xml

Architecture

Main (console menu)
  -> EmployeeService (validation, user messages)
    -> EmployeeDAO (interface)
      -> EmployeeDAOImpl (JDBC)
        -> DBConnection
          -> MySQL (ems_db)

• Main reads user input and shows the menu. It contains no business logic.
• EmployeeService validates the input, calls the DAO, and prints the result messages.
• EmployeeDAO defines the database operations. EmployeeDAOImpl implements them using JDBC PreparedStatement and try-with-resources.
• The service accepts a DAO through its constructor, so the tests can pass in a mocked DAO and run without a database.
• The DAO has no console output and does not call the service, which keeps the layers separate.

Setup

Requirements

• Java 21
• Maven
• MySQL

1. Create the database

Run the schema file. It creates the ems_db database, the employees table, and a few sample rows:

mysql -u root -p < schema.sql

Delete the INSERT block in schema.sql first if you want an empty table.

2. Add your database credentials

Copy the template and fill in your own values:

cp db.properties.example db.properties

db.url=jdbc:mysql://localhost:3306/ems_db
db.username=your_username
db.password=your_password

db.properties is listed in .gitignore, so your password is never committed.

3. Build

mvn clean compile

Running the App

Open the project in IntelliJ IDEA (or any Java IDE) and run Main. Run it from the project root folder, because the app looks for db.properties there.

Running the Tests

mvn test

There are 48 unit tests: 20 for the Employee model and 28 for EmployeeService. The service tests use Mockito to mock the DAO, so they do not need a database or a db.properties file.

Author

Ashutosh Singh