JWT vs session-based decision in Spring Boot - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a JWT token with a secret key.

Spring Boot

String token = Jwts.builder().setSubject(user.getUsername()).signWith([1]).compact();

Drag options to blanks, or click blank then click option'

ASignatureAlgorithm.HS512

Bnew SecretKeySpec(secret.getBytes(), "HmacSHA256")

Cnull

DKeys.secretKeyFor(SignatureAlgorithm.HS256)

Attempts:

3 left

💡 Hint

Common Mistakes

Using null or incorrect signature algorithm causes errors.

Use Keys.secretKeyFor(SignatureAlgorithm.HS256) to generate a secure secret key for signing the JWT.

2fill in blank

medium

Complete the code to store user info in HTTP session.

Spring Boot

HttpSession session = request.getSession(); session.setAttribute("[1]", user);

Drag options to blanks, or click blank then click option'

AcurrentUser

Buser

CsessionUser

DuserInfo

Attempts:

3 left

💡 Hint

Common Mistakes

Using inconsistent attribute names causes retrieval issues.

The attribute name user is commonly used to store the user object in session.

3fill in blank

hard

Fix the error in the JWT validation code by completing the missing method.

Spring Boot

Jwts.parserBuilder().setSigningKey([1]).build().parseClaimsJws(token);

Drag options to blanks, or click blank then click option'

AsecretKey

Bnull

Ctoken

Duser.getPassword()

Attempts:

3 left

💡 Hint

Common Mistakes

Passing null or wrong key causes exceptions.

The setSigningKey method requires the secret key used to sign the token for validation.

4fill in blank

hard

Fill both blanks to configure session timeout and secure cookie.

Spring Boot

session.setMaxInactiveInterval([1]); response.addCookie(new Cookie("JSESSIONID", [2]));

Drag options to blanks, or click blank then click option'

A1800

B"secureValue"

C"HttpOnly"

D3600

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong timeout units or invalid cookie values.

Set session timeout to 1800 seconds (30 minutes) and add a secure cookie value.

5fill in blank

hard

Fill all three blanks to create a JWT with claims and expiration.

Spring Boot

String jwt = Jwts.builder().setSubject([1]).claim("role", [2]).setExpiration([3]).signWith(secretKey).compact();

Drag options to blanks, or click blank then click option'

Auser.getUsername()

B"admin"

Cnew Date(System.currentTimeMillis() + 3600000)

Duser.getPassword()

Attempts:

3 left

💡 Hint

Common Mistakes

Using password as subject or invalid expiration date.

Use the username as subject, set role claim to "admin", and expiration to 1 hour from now.

Practice

1. Which statement best describes JWT authentication in Spring Boot?

easy

A. User info is stored on the server and tracked with cookies.

B. User info is stored only in the database without tokens or sessions.

C. User info is stored in a token sent with each request, no server storage needed.

D. User info is stored in browser local storage only.

Solution

1. Step 1: Understand JWT storage method

   JWT stores user information inside a token that is sent with every request, so the server does not need to keep session data.

2. Step 2: Compare with session storage

   Sessions store user info on the server and use cookies to track users, unlike JWT which is stateless.

3. Final Answer:

   User info is stored in a token sent with each request, no server storage needed. -> Option C

4. Quick Check:

   JWT = token-based stateless auth [OK]

Hint: JWT stores info in tokens, sessions store on server [OK]

Common Mistakes:

• Confusing JWT with session storage
• Thinking JWT requires server-side storage
• Believing JWT info is only in browser storage

2. Which code snippet correctly sets a session attribute in Spring Boot?

easy

A. request.getSession().setAttribute("user", userObject);

B. request.setSessionAttribute("user", userObject);

C. session.setAttribute("user", userObject);

D. request.session().setAttribute("user", userObject);

Solution

1. Step 1: Recall correct method to get session

   In Spring Boot, you get the session from the request using request.getSession().

2. Step 2: Set attribute on session object

   Then call setAttribute("user", userObject) on the session to store data.

3. Final Answer:

   request.getSession().setAttribute("user", userObject); -> Option A

4. Quick Check:

   Use getSession() then setAttribute() [OK]

Hint: Use request.getSession() before setAttribute [OK]

Common Mistakes:

• Calling setAttribute directly on request
• Using incorrect method names like setSessionAttribute
• Trying to call session() as a method on request

3. Given this Spring Boot code snippet using JWT, what is the expected behavior?

String token = jwtUtil.generateToken(userDetails);
response.setHeader("Authorization", "Bearer " + token);
// No session is created on server

medium

A. User info is stored on server session and token is ignored.

B. Token is sent to client; server remains stateless without session.

C. Session is created on server with token stored inside.

D. Token is stored in server memory for each user.

Solution

1. Step 1: Analyze token generation and response header

   The code generates a JWT token and sends it in the Authorization header to the client.

2. Step 2: Note server session behavior

   The comment says no session is created on the server, meaning the server stays stateless.

3. Final Answer:

   Token is sent to client; server remains stateless without session. -> Option B

4. Quick Check:

   JWT = stateless token sent to client [OK]

Hint: JWT sends token, no server session created [OK]

Common Mistakes:

• Assuming server stores token in session
• Thinking token is ignored by server
• Believing token is stored in server memory

4. Identify the error in this Spring Boot session code snippet:

HttpSession session = request.getSession(false);
session.setAttribute("user", userObject);

medium

A. Session attributes cannot store user objects.

B. setAttribute method does not exist on HttpSession.

C. request.getSession(false) always creates a new session.

D. Using getSession(false) may return null causing NullPointerException.

Solution

1. Step 1: Understand getSession(false) behavior

   getSession(false) returns existing session or null if none exists; it does not create a new session.

2. Step 2: Check for possible null usage

   If session is null, calling setAttribute causes NullPointerException.

3. Final Answer:

   Using getSession(false) may return null causing NullPointerException. -> Option D

4. Quick Check:

   getSession(false) can return null [OK]

Hint: getSession(false) may return null, check before use [OK]

Common Mistakes:

• Assuming getSession(false) always returns a session
• Believing setAttribute is invalid method
• Thinking sessions cannot store objects

5. You are building a Spring Boot app that must scale across many servers without sticky sessions. Which authentication method should you choose and why?

hard

A. Use JWT because it is stateless and does not require server session storage.

B. Use JWT but store tokens in server memory for faster access.

C. Use session-based authentication with distributed cache to share sessions.

D. Use session-based authentication because it stores user info on the server.

Solution

1. Step 1: Understand scaling needs

   Scaling across many servers without sticky sessions means no single server holds user session data.

2. Step 2: Compare authentication methods

   Session-based auth stores user info on server, requiring session sharing or sticky sessions, which complicates scaling.

3. Step 3: Choose JWT for statelessness

   JWT stores user info in tokens sent with requests, so servers remain stateless and scaling is easier.

4. Final Answer:

   Use JWT because it is stateless and does not require server session storage. -> Option A

5. Quick Check:

   Stateless JWT best for scalable multi-server apps [OK]

Hint: Stateless JWT fits multi-server scaling best [OK]

Common Mistakes:

• Choosing sessions without sticky sessions or shared cache
• Thinking JWT requires server memory storage
• Ignoring stateless benefits of JWT