Validation Demo

A comprehensive Spring Boot application demonstrating various validation techniques using Jakarta Bean Validation annotations.

📋 Table of Contents

• Overview
• Technologies Used
• Project Structure
• Getting Started
• API Endpoints
• Validation Rules
• Usage Examples
• Error Handling
• Video Tutorial
• Contributing

🎯 Overview

This project showcases the implementation of robust data validation in a Spring Boot REST API, featuring both standard Jakarta Bean Validation and advanced custom validation annotations. It demonstrates how to validate student information using built-in constraints, custom parameterized validators, and cross-field validation techniques, all with comprehensive error handling and meaningful error responses.

Key Features:

• 📋 Standard Jakarta Bean Validation annotations
• 🎯 Custom parameterized validation annotations (@MinimumAge)
• 🔄 Cross-field validation for data consistency (@AgeMatchesDateOfBirth)
• 🚨 Global exception handling with structured error responses
• 📝 Comprehensive validation rule documentation

🛠 Technologies Used

• Java 21
• Spring Boot 3.5.5
• Spring Boot Starter Web - For REST API functionality
• Spring Boot Starter Validation - For Jakarta Bean Validation
• Lombok 1.18.38 - For reducing boilerplate code
• Maven - For dependency management and build automation

📁 Project Structure

validation-demo/
├── src/
│   ├── main/
│   │   ├── java/com/learnwithiftekhar/validation_demo/
│   │   │   ├── ValidationDemoApplication.java    # Main Spring Boot application
│   │   │   ├── Student.java                      # Student model with validation annotations
│   │   │   ├── StudentController.java            # REST controller for student operations
│   │   │   └── validation/                       # Custom validation package
│   │   │       ├── CustomValidationException.java    # Global exception handler
│   │   │       ├── MinimumAge.java               # Custom minimum age validation annotation
│   │   │       ├── MinimumAgeValidator.java      # Validator for minimum age constraint
│   │   │       ├── AgeMatchesDateOfBirth.java    # Cross-field validation annotation
│   │   │       └── AgeValidator.java             # Validator for age/DOB consistency
│   │   └── resources/
│   │       └── application.properties            # Application configuration
│   └── test/
│       └── java/com/learnwithiftekhar/validation_demo/
│           └── ValidationDemoApplicationTests.java
├── pom.xml                                       # Maven configuration
└── README.md                                     # Project documentation

🚀 Getting Started

Prerequisites

• Java 21 or higher
• Maven 3.6+ (or use the included Maven wrapper)

Installation & Running

1. Clone the repository

   git clone https://github.com/learnwithiftekhar/spring-boot-data-validation.git
   cd spring-boot-data-validation

2. Build the project

   ./mvnw clean compile

3. Run the application

   ./mvnw spring-boot:run

4. Alternative: Run with Java

   ./mvnw clean package
   java -jar target/validation-demo-0.0.1-SNAPSHOT.jar

The application will start on http://localhost:8080

🌐 API Endpoints

POST /

Creates/validates a student record.

Request Body: Student JSON object Response: Validated Student object or validation errors Content-Type: application/json

✨ Custom Validation Features

This project implements advanced custom validation annotations beyond standard Jakarta Bean Validation:

🎯 Custom Annotations

@MinimumAge

A parameterized validation annotation that allows specifying a minimum age requirement.

• Target: Fields (applied to dateOfBirth)
• Parameter: value - minimum age in years
• Validator: MinimumAgeValidator.class
• Usage: @MinimumAge(value = 17, message = "Student must be at least 17 years old.")

@AgeMatchesDateOfBirth

A class-level validation that ensures consistency between age and dateOfBirth fields.

• Target: Class level (applied to entire Student class)
• Validator: AgeValidator.class
• Purpose: Cross-field validation to prevent data inconsistencies
• Usage: @AgeMatchesDateOfBirth

🔧 Validator Implementation

• MinimumAgeValidator: Calculates age from date of birth and validates against minimum requirement
• AgeValidator: Performs cross-field validation ensuring the provided age matches the calculated age from date of birth

✅ Validation Rules

The Student model includes comprehensive validation rules:

Field	Validation Rules	Error Messages
Class Level	• @AgeMatchesDateOfBirth (Cross-field validation)	• "The provided age does not match the date of birth"
studentId	• Required (not blank) • Pattern: ^S\d{5}$	• "Student ID is required." • "Student id must be in the format 'S' followed by 5 digits (e.g. S12345)"
firstName	• Required (not blank)	• "First Name is required."
middleName	• Cannot be null	• "Middle Name cannot be null."
lastName	• Required (not blank)	• "Last Name is required."
age	• Required • Min: 17 • Max: 100	• "Age is required." • "Student must be at least 17 years old" • "Student age must not be greater than 100 years."
dateOfBirth	• Required • Must be in the past • @MinimumAge(17) (Custom validation)	• "Date of birth is required." • "Date of birth must be in the past." • "Student must be at least 17 years old."
expectedGraduationDate	• Required • Must be in the future	• "Expected graduation date is required." • "Graduation date must be in the future."
email	• Required • Valid email format	• "Email address is required." • "Please provide valid email address."
enrolledCourses	• Cannot be empty	• "Student must enrolled in at least one course."
gpa	• Required • Min: 0.0 • Max: 4.0 • Format: X.XX	• "GPA is required." • "GPA must be at least 0.0" • "GPA must not exceed 4.0" • "GPA must have at most 1 integer and 2 fraction digits."

📝 Usage Examples

Valid Student Request

curl -X POST http://localhost:8080/ \
  -H "Content-Type: application/json" \
  -d '{
    "studentId": "S12345",
    "firstName": "John",
    "middleName": "Michael",
    "lastName": "Doe",
    "age": 20,
    "dateOfBirth": "2003-05-15",
    "expectedGraduationDate": "2026-06-15",
    "email": "john.doe@example.com",
    "enrolledCourses": ["Computer Science 101", "Mathematics"],
    "gpa": "3.75"
  }'

Response (200 OK):

{
  "studentId": "S12345",
  "firstName": "John",
  "middleName": "Michael",
  "lastName": "Doe",
  "age": 20,
  "dateOfBirth": "2003-05-15",
  "expectedGraduationDate": "2026-06-15",
  "email": "john.doe@example.com",
  "enrolledCourses": ["Computer Science 101", "Mathematics"],
  "gpa": 3.75
}

Invalid Student Request

curl -X POST http://localhost:8080/ \
  -H "Content-Type: application/json" \
  -d '{
    "studentId": "12345",
    "firstName": "",
    "age": 15,
    "email": "invalid-email",
    "gpa": "5.0"
  }'

Response (400 Bad Request):

{
  "studentId": "Student id must be in the format 'S' followed by 5 digits (e.g. S12345)",
  "firstName": "First Name is required.",
  "middleName": "Middle Name cannot be null.",
  "lastName": "Last Name is required.",
  "age": "Student must be at least 17 years old",
  "dateOfBirth": "Date of birth is required.",
  "expectedGraduationDate": "Expected graduation date is required.",
  "email": "Please provide valid email address.",
  "enrolledCourses": "Student must enrolled in at least one course.",
  "gpa": "GPA must not exceed 4.0"
}

🚨 Error Handling

The application includes a global exception handler (CustomValidationException) that:

• Catches MethodArgumentNotValidException for validation errors
• Returns structured JSON responses with field-specific error messages
• Uses HTTP status code 400 (Bad Request) for validation failures
• Provides clear, actionable error messages for each validation failure

Error response format:

{
  "fieldName": "error message",
  "anotherField": "another error message"
}

🧪 Testing

Run the tests using:

./mvnw test

🎥 Video Tutorial

This project is featured in a comprehensive YouTube tutorial that walks through the implementation step by step:

📺 Spring Boot Data Validation Tutorial

The tutorial covers:

• Setting up Spring Boot with validation dependencies
• Creating validation annotations for different data types
• Implementing custom error handling
• Testing validation scenarios with real examples
• Best practices for data validation in Spring Boot

🤝 Contributing

1. Fork the repository
2. Create your feature branch (git checkout -b feature/amazing-feature)
3. Commit your changes (git commit -m 'Add some amazing feature')
4. Push to the branch (git push origin feature/amazing-feature)
5. Open a Pull Request

Development Guidelines

• Follow Java naming conventions
• Add appropriate validation annotations for new fields
• Include comprehensive error messages
• Update tests when adding new features
• Ensure all tests pass before submitting

📄 License

This project is created for educational purposes to demonstrate Spring Boot validation techniques.

👨‍💻 Author

Learn with Iftekhar

• GitHub: @learnwithiftekhar

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This project demonstrates best practices for data validation in Spring Boot applications using Jakarta Bean Validation annotations.