Cache configuration in Spring Boot - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to enable caching in a Spring Boot application.

Spring Boot

@SpringBootApplication
public class Application {
    public static void main(String[] args) {
        SpringApplication.[1](Application.class, args);
    }
}

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

Arun

Bstart

Claunch

Dexecute

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'start' or 'launch' instead of 'run' causes errors.

Forgetting to call any method to start the app.

The SpringApplication.run() method starts the Spring Boot application.

2fill in blank

medium

Complete the annotation to enable caching in a Spring Boot application.

Spring Boot

@Configuration
@[1]
public class CacheConfig {
}

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

AEnableCaching

BCacheable

CCacheConfig

DEnableCache

Attempts:

3 left

💡 Hint

Common Mistakes

Using @Cacheable on configuration class instead of @EnableCaching.

Misspelling the annotation name.

The @EnableCaching annotation activates Spring's annotation-driven cache management capability.

3fill in blank

hard

Fix the error in the cacheable method annotation to cache the result.

Spring Boot

@Service
public class ProductService {

    @Cacheable(cacheNames = "products", key = "#[1]")
    public Product getProductById(Long id) {
        // fetch product
    }
}

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

Akey

BproductId

Cid

Dvalue

Attempts:

3 left

💡 Hint

Common Mistakes

Using a key that does not match any parameter causes runtime errors.

Omitting the '#' in the SpEL expression.

The method parameter is named id, so the key expression must use #id to cache by that parameter.

4fill in blank

hard

Fill both blanks to configure a cache manager bean using ConcurrentMapCacheManager.

Spring Boot

@Configuration
public class CacheConfig {

    @Bean
    public CacheManager cacheManager() {
        return new [1](List.of("[2]"));
    }
}

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

AConcurrentMapCacheManager

BRedisCacheManager

Cproducts

Dusers

Attempts:

3 left

💡 Hint

Common Mistakes

Using RedisCacheManager without Redis dependencies.

Mismatching cache names causes cache misses.

The ConcurrentMapCacheManager is a simple cache manager using a concurrent map. The cache name here is 'products'.

5fill in blank

hard

Fill all three blanks to create a cacheable method that caches by user ID and cache name 'users'.

Spring Boot

@Service
public class UserService {

    @Cacheable(cacheNames = "[1]", key = "#[2]")
    public User getUserById(Long [3]) {
        // fetch user
    }
}

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

Ausers

Bid

CuserId

Dproducts

Attempts:

3 left

💡 Hint

Common Mistakes

Using different names for key and parameter causes cache failures.

Using wrong cache names leads to no caching.

The cache name is 'users'. The method parameter is named 'id', so the key expression uses '#id'. The parameter name in the method must match 'id'.

Practice

1. What is the primary purpose of using cache configuration in a Spring Boot application?

easy

A. To temporarily store data and speed up application performance

B. To permanently save data to the database

C. To encrypt sensitive data before sending it

D. To manage user authentication and authorization

Solution

1. Step 1: Understand caching concept

   Caching stores data temporarily to avoid repeated processing or fetching.

2. Step 2: Identify caching benefit in Spring Boot

   It speeds up the app by reusing stored data instead of recalculating or fetching again.

3. Final Answer:

   To temporarily store data and speed up application performance -> Option A

4. Quick Check:

   Cache = Temporary storage for speed [OK]

Hint: Cache means temporary storage to speed up apps [OK]

Common Mistakes:

• Confusing cache with permanent database storage
• Thinking cache encrypts data
• Mixing cache with security features

2. Which annotation is used to enable caching support in a Spring Boot application?

easy

A. @EnableCaching

B. @Cacheable

C. @CacheConfig

D. @CachePut

Solution

1. Step 1: Recall Spring Boot caching setup

   To activate caching, Spring Boot requires a special annotation on a configuration class.

2. Step 2: Identify the correct annotation

   @EnableCaching enables the caching mechanism globally in the app.

3. Final Answer:

   @EnableCaching -> Option A

4. Quick Check:

   @EnableCaching activates caching [OK]

Hint: Enable caching with @EnableCaching annotation [OK]

Common Mistakes:

• Using @Cacheable to enable caching (it marks methods, not enable)
• Confusing @CachePut with enabling caching
• Thinking @CacheConfig enables caching globally

3. Given the code below, what will be the output when getUser(1) is called twice?

@Cacheable("users")
public User getUser(int id) {
    System.out.println("Fetching user from DB");
    return new User(id, "Name" + id);
}

medium

A. Fetching user from DB printed twice, two User objects returned

B. No output printed, both calls return null

C. Fetching user from DB printed once, but both calls create new User

D. Fetching user from DB printed once, second call returns cached User

Solution

1. Step 1: Understand @Cacheable behavior

   The first call runs the method and caches the result; subsequent calls return cached data.

2. Step 2: Analyze output for two calls

   "Fetching user from DB" prints only once on first call; second call uses cache, no print.

3. Final Answer:

   Fetching user from DB printed once, second call returns cached User -> Option D

4. Quick Check:

   @Cacheable caches after first call [OK]

Hint: First call runs method, next calls use cache [OK]

Common Mistakes:

• Assuming method runs every time ignoring cache
• Thinking cache returns null if not found
• Confusing @Cacheable with @CachePut behavior

4. Identify the error in this cache configuration snippet:

@Configuration
@EnableCaching
public class CacheConfig {
    @Bean
    public CacheManager cacheManager() {
        return new CacheManager();
    }
}

medium

A. Missing @Cacheable annotation on methods

B. CacheManager is an interface and cannot be instantiated directly

C. Missing @EnableCaching annotation

D. CacheManager bean method should be static

Solution

1. Step 1: Check CacheManager instantiation

   CacheManager is an interface; you cannot create it with new CacheManager().

2. Step 2: Correct way to create CacheManager bean

   You must return a concrete implementation like ConcurrentMapCacheManager.

3. Final Answer:

   CacheManager is an interface and cannot be instantiated directly -> Option B

4. Quick Check:

   CacheManager interface needs implementation [OK]

Hint: CacheManager is interface; use implementation class [OK]

Common Mistakes:

• Trying to instantiate interface directly
• Forgetting to add @EnableCaching
• Thinking @Cacheable is needed on config class

5. You want to configure a cache in Spring Boot that stores user data and expires entries after 10 minutes. Which approach correctly combines cache configuration and expiration?

hard

A. Use @EnableCaching and define a ConcurrentMapCacheManager bean with TTL set to 10 minutes

B. Use @CachePut and manually remove cache entries after 10 minutes

C. Use @EnableCaching and configure a CaffeineCacheManager with expiry policy of 10 minutes

D. Use @Cacheable with a parameter to set expiration time to 10 minutes

Solution

1. Step 1: Understand cache expiration support

   ConcurrentMapCacheManager does not support TTL (time to live) expiration by default.

2. Step 2: Identify cache manager with TTL support

   CaffeineCacheManager supports expiration policies like 10-minute TTL.

3. Step 3: Evaluate options

   @Cacheable does not accept expiration parameters; @CachePut updates cache but does not manage expiration automatically.

4. Final Answer:

   Use @EnableCaching and configure a CaffeineCacheManager with expiry policy of 10 minutes -> Option C

5. Quick Check:

   CaffeineCacheManager supports TTL expiration [OK]

Hint: Use CaffeineCacheManager for TTL expiration [OK]

Common Mistakes:

• Assuming ConcurrentMapCacheManager supports TTL
• Trying to set expiration via @Cacheable annotation
• Using @CachePut to handle expiration manually