Redis as cache provider 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

Cexecute

Dlaunch

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 support in Spring Boot.

Spring Boot

@Configuration
[1]
public class CacheConfig {
}

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A@EnableScheduling

B@EnableTransactionManagement

C@EnableAsync

D@EnableCaching

Attempts:

3 left

💡 Hint

Common Mistakes

Using @EnableScheduling or other unrelated annotations.

Forgetting to add any caching annotation.

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

3fill in blank

hard

Fix the error in the Redis cache manager bean definition.

Spring Boot

@Bean
public RedisCacheManager cacheManager(RedisConnectionFactory factory) {
    return RedisCacheManager.[1](factory).build();
}

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Abuilder

BBuilder

Ccreate

DbuilderFactory

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'create' or 'Builder' causes compilation errors.

Using incorrect method names for builder pattern.

RedisCacheManager.builder(factory) returns a builder to configure and build the cache manager.

4fill in blank

hard

Fill both blanks to configure a RedisTemplate bean with String keys and values.

Spring Boot

@Bean
public RedisTemplate<String, String> redisTemplate(RedisConnectionFactory factory) {
    RedisTemplate<String, String> template = new RedisTemplate<>();
    template.setConnectionFactory([1]);
    template.setKeySerializer([2]);
    return template;
}

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Afactory

Bnew StringRedisSerializer()

Cnew GenericJackson2JsonRedisSerializer()

DconnectionFactory

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong serializer for keys causes data issues.

Passing wrong variable name for connection factory.

The RedisTemplate needs the RedisConnectionFactory to connect and a StringRedisSerializer to serialize keys as strings.

5fill in blank

hard

Fill both blanks to create a cacheable service method with Redis cache.

Spring Boot

public class UserService {

    @Cacheable(cacheNames = [1])
    public User getUserById([2] id) {
        // fetch user from database
        return userRepository.findById(id);
    }
}

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

A"users"

BLong

Cint

D"userCache"

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong cache name string or missing quotes.

Using wrong parameter type like int instead of Long.

The @Cacheable annotation requires a cache name string like 'userCache'. The method parameter type for id is Long.

Practice

1. What is the main purpose of using Redis as a cache provider in a Spring Boot application?

easy

A. To store frequently accessed data in memory for faster retrieval

B. To replace the database completely

C. To handle user authentication

D. To serve static web pages

Solution

1. Step 1: Understand Redis caching role

   Redis stores data in memory, which is much faster than disk storage.

2. Step 2: Identify caching benefit in Spring Boot

   Caching reduces database calls by storing frequently used data temporarily.

3. Final Answer:

   To store frequently accessed data in memory for faster retrieval -> Option A

4. Quick Check:

   Redis cache = fast data access [OK]

Hint: Redis cache speeds up data access by storing in memory [OK]

Common Mistakes:

• Thinking Redis replaces the database
• Confusing caching with authentication
• Assuming Redis serves static files

2. Which annotation is used in Spring Boot to enable caching support when using Redis?

easy

A. @RedisCache

B. @Cacheable

C. @EnableCaching

D. @CacheConfig

Solution

1. Step 1: Identify the annotation to activate caching

   @EnableCaching is used on a configuration class to turn on caching support.

2. Step 2: Differentiate from other annotations

   @Cacheable marks methods to cache results, but does not enable caching globally.

3. Final Answer:

   @EnableCaching -> Option C

4. Quick Check:

   Enable caching = @EnableCaching [OK]

Hint: Use @EnableCaching to activate caching in Spring Boot [OK]

Common Mistakes:

• Confusing @Cacheable with enabling caching
• Using non-existent @RedisCache annotation
• Mistaking @CacheConfig for enabling caching

3. Given the following Spring Boot method with Redis caching:

@Cacheable("books")
public Book findBookById(Long id) {
    System.out.println("Fetching from DB");
    return bookRepository.findById(id).orElse(null);
}

What will be printed if findBookById(1L) is called twice in a row?

medium

A. Fetching from DB

B. No output

C. Fetching from DB
Fetching from DB

D. Error at runtime

Solution

1. Step 1: Understand @Cacheable behavior

   The first call caches the result and prints "Fetching from DB".

2. Step 2: Analyze second call output

   The second call returns cached data without executing method body, so no print.

3. Final Answer:

   Fetching from DB -> Option A

4. Quick Check:

   Cache avoids repeated DB fetch print [OK]

Hint: First call prints, second uses cache silently [OK]

Common Mistakes:

• Expecting print on every call
• Thinking cache disables method
• Assuming runtime error due to caching

4. Consider this Spring Boot Redis cache configuration snippet:

@Bean
public RedisCacheManager cacheManager(RedisConnectionFactory factory) {
    return RedisCacheManager.builder(factory).build();
}

If the Redis server is down, what will happen when the application tries to cache data?

medium

A. Application falls back to file-based cache

B. Application throws a runtime exception and crashes

C. Data is cached in memory without Redis

D. Caching silently fails but application continues

Solution

1. Step 1: Understand RedisCacheManager dependency

   RedisCacheManager requires a running Redis server to store cache data.

2. Step 2: Analyze behavior if Redis is down

   Without Redis, cache operations typically fail silently and the application continues unless explicitly configured to fail.

3. Final Answer:

   Caching silently fails but application continues -> Option D

4. Quick Check:

   Redis down usually does not crash app by default [OK]

Hint: Redis down causes silent cache failure unless handled [OK]

Common Mistakes:

• Assuming fallback to memory cache
• Thinking caching silently fails
• Expecting file-based fallback

5. You want to cache the result of a method that returns a list of users filtered by role. Which is the best way to use Redis caching in Spring Boot to avoid caching empty or null results?

public List<User> getUsersByRole(String role) {
    // fetch users
}

hard

A. Use @CachePut to always update cache

B. Use @Cacheable with condition = "#result != null && !#result.isEmpty()"

C. Manually check and cache inside the method

D. Use @Cacheable without any condition

Solution

1. Step 1: Understand caching empty results issue

   Caching empty or null results wastes cache space and may cause stale data.

2. Step 2: Use @Cacheable condition attribute

   Adding condition "#result != null && !#result.isEmpty()" caches only meaningful results.

3. Final Answer:

   Use @Cacheable with condition = "#result != null && !#result.isEmpty()" -> Option B

4. Quick Check:

   Condition filters empty cache entries [OK]

Hint: Use @Cacheable condition to skip empty results [OK]

Common Mistakes:

• Caching all results including empty lists
• Manually caching inside method instead of annotation
• Using @CachePut which always updates cache