Redis as cache provider in Spring Boot - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is Redis and why is it used as a cache provider in Spring Boot?

Redis is an in-memory data store that is very fast. It is used as a cache provider in Spring Boot to store frequently accessed data temporarily, so the application can get data quickly without hitting the database every time.

beginner

How do you enable Redis caching in a Spring Boot application?

You add the Spring Boot starter for Redis and caching, then add @EnableCaching annotation in your main application class. This tells Spring Boot to use caching features and Redis as the cache store.

beginner

What annotation is used to cache the result of a method in Spring Boot with Redis?

The @Cacheable annotation is used on a method to tell Spring Boot to cache its result in Redis. When the method is called again with the same parameters, the cached result is returned instead of running the method again.

intermediate

What is the role of RedisTemplate in Spring Boot Redis caching?

RedisTemplate is a helper class in Spring Boot that simplifies Redis operations like saving, retrieving, and deleting cache data. It handles the connection and data serialization for you.

intermediate

How can you configure the expiration time for cached data in Redis with Spring Boot?

You can set the expiration time (TTL) for cached data by configuring the cache manager or using Redis commands. In Spring Boot, you can customize the RedisCacheManager bean to set TTL for caches so data expires after a set time.

Which annotation enables caching support in a Spring Boot application?

A @CacheEvict

B @Cacheable

C @EnableCaching

D @CachePut

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

What does the @Cacheable annotation do?

A Deletes cache entries

B Caches the result of a method

C Updates cache entries

D Disables caching

@Cacheable caches the result of a method so future calls with the same parameters return cached data.

What type of data store is Redis?

A In-memory data store

B Relational database

C File system

D NoSQL document store

Redis is an in-memory data store, which makes it very fast for caching.

Which Spring Boot class helps with Redis operations like saving and retrieving data?

A JdbcTemplate

B MongoTemplate

C CacheManager

D RedisTemplate

RedisTemplate simplifies Redis operations such as saving and retrieving cache data.

How do you set a time-to-live (TTL) for cached data in Redis with Spring Boot?

A Configuring RedisCacheManager with TTL settings

B Using @Cacheable only

C Using @EnableCaching

D Setting TTL is not possible

You configure RedisCacheManager bean to set TTL for cached data so it expires after a certain time.

Explain how Redis works as a cache provider in a Spring Boot application.

Think about why caching helps and how Redis fits in.

Describe the steps to set up Redis caching in a Spring Boot project.

Focus on dependencies, annotations, and configuration.

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