JWT generation in Spring Boot - Mini Project: Build & Apply

JWT Generation with Spring Boot

📖 Scenario: You are building a simple Spring Boot application that needs to create JSON Web Tokens (JWT) for user authentication. JWTs are like digital ID cards that prove who the user is.In this project, you will create the data needed for the token, set up a secret key, generate the token using the key and data, and finally complete the token creation method.

🎯 Goal: Build a Spring Boot service that generates a JWT token string using a username and a secret key.

📋 What You'll Learn

Create a Map<String, Object> called claims with a single entry: key "username" and value "user123".

Create a String variable called secretKey with the value "mySecretKey12345".

Use the Jwts.builder() to build a JWT token with the claims and sign it with the secretKey using SignatureAlgorithm.HS256.

Complete the generateToken() method to return the generated JWT token string.

💡 Why This Matters

🌍 Real World

JWT tokens are widely used in web applications to securely transmit user identity and permissions between client and server.

💼 Career

Understanding JWT generation is essential for backend developers working on authentication and authorization in modern web services.

1

Create the JWT claims data

Create a Map<String, Object> called claims and add one entry with key "username" and value "user123".

Spring Boot

import java.util.Map;
import java.util.HashMap;

public class JwtService {

    // Create claims map with username
    // Your code here

}

Need a hint?

Use new HashMap<>() to create the map and put to add the username.

2

Add the secret key for signing

Add a String variable called secretKey and set it to "mySecretKey12345".

Spring Boot

import java.util.Map;
import java.util.HashMap;

public class JwtService {

    Map claims = new HashMap();
    {
        claims.put("username", "user123");
    }

    // Add secretKey variable
    // Your code here

}

Need a hint?

Declare a String variable and assign the exact secret key string.

3

Build the JWT token using claims and secret key

Use io.jsonwebtoken.Jwts.builder() to create a JWT token. Set the claims with setClaims(claims) and sign it with signWith(SignatureAlgorithm.HS256, secretKey). Store the result in a String variable called token.

Spring Boot

import java.util.Map;
import java.util.HashMap;
import io.jsonwebtoken.Jwts;
import io.jsonwebtoken.SignatureAlgorithm;

public class JwtService {

    Map claims = new HashMap();
    {
        claims.put("username", "user123");
    }

    String secretKey = "mySecretKey12345";

    // Build JWT token string
    // Your code here

}

Need a hint?

Chain the builder methods to set claims and sign the token, then call compact() to get the token string.

4

Complete the generateToken() method

Create a public method generateToken() that returns a String. Move the token generation code inside this method and return the token string.

Spring Boot

import java.util.Map;
import java.util.HashMap;
import io.jsonwebtoken.Jwts;
import io.jsonwebtoken.SignatureAlgorithm;

public class JwtService {

    Map claims = new HashMap();
    {
        claims.put("username", "user123");
    }

    String secretKey = "mySecretKey12345";

    // Create generateToken() method
    // Your code here

}

Need a hint?

Wrap the token creation code inside a method and return the token string.