Custom Annotation in Spring Boot with JWT Authentication

📌 What is this project?

This project demonstrates how to create a custom annotation in a Spring Boot application while implementing JWT-based authentication. The custom annotation @InjectUserContext allows automatic injection of user details (like username and roles) into API methods, simplifying authentication and authorization workflows. The project also includes:

• Spring Security for authentication and authorization.
• JWT (JSON Web Token) for secure API access.
• H2 in-memory database for easy testing.
• Aspect-Oriented Programming (AOP) to handle the custom annotation.
• Global Exception Handling for better error management.

It is a complete authentication system that demonstrates best practices for user authentication and role-based access control in Spring Boot.

🚀 How to Run Your Spring Boot Project (With Custom Annotation & JWT Authentication)

Now that your project is set up correctly, follow these step-by-step instructions to run and test your application.

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🔹 1️⃣ Ensure Your Environment is Ready

Before running the project, make sure you have:

• ✅ Java 17 (or the version specified in pom.xml)
• ✅ Maven Installed (mvn -v to check)
• ✅ IntelliJ IDEA / VS Code / Eclipse (Any Java IDE)
• ✅ Postman / cURL (for API testing)

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🔹 2️⃣ Build & Run the Application

Option 1: Using Your IDE (IntelliJ / Eclipse / VS Code)

1. Open the project in IntelliJ IDEA (or your preferred IDE).
2. Navigate to the CustomAnnotationApplication.java class.
3. Click Run ▶️ OR use the shortcut:

Mac: Cmd + Shift + F10

Windows/Linux: Ctrl + Shift + F10

Option 2: Using Maven (Terminal)

Run the following commands in the project root directory:

# 1️⃣ Clean previous builds (optional)
mvn clean

# 2️⃣ Build the project
mvn install

# 3️⃣ Run the application
mvn spring-boot:run

Your Spring Boot application should now start on http://localhost:8080.

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🔹 3️⃣ Verify the H2 Database (Optional)

Since we are using H2 in-memory database, you can check the database via H2 Console:

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

Click Connect to view the users table.

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🔹 4️⃣ Test API Endpoints (Authentication & Custom Annotation)

Now let's test your APIs using Postman or cURL.

📌 Login API (Get JWT Token)

POST http://localhost:8080/api/auth/login

Request Body (JSON)

{
  "username": "admin",
  "password": "admin123"
}

Response (JSON)

{
  "token": "eyJhbGciOiJIUzI1NiIsInR5..."
}

✅ Copy this token for the next requests.

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📌 Access Secured API (@InjectUserContext Custom Annotation)

GET http://localhost:8080/api/auth/me

Headers

Authorization: Bearer <PASTE_YOUR_JWT_HERE>

Response (JSON)

{
  "username": "admin",
  "roles": "ROLE_ADMIN"
}

If you don’t send a token, you should get:

{
  "error": "Unauthorized"
}

✅ This confirms that the JWT authentication and custom annotation are working.