@CacheEvict for invalidation in Spring Boot - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the @CacheEvict annotation in Spring Boot?

The @CacheEvict annotation is used to remove or invalidate cache entries when a method is called, ensuring that stale data is not served from the cache.

beginner

How do you specify which cache to evict using @CacheEvict?

You specify the cache name(s) to evict using the 'value' or 'cacheNames' attribute, for example: @CacheEvict(value = "usersCache").

intermediate

What does the 'allEntries' attribute do in @CacheEvict?

Setting 'allEntries = true' removes all entries from the specified cache instead of just the one related to the method's key.

intermediate

Explain the use of 'beforeInvocation' attribute in @CacheEvict.

The 'beforeInvocation' attribute controls whether the cache eviction happens before the method runs (true) or after it completes (false). By default, eviction happens after the method runs.

intermediate

Can @CacheEvict be used to evict multiple caches at once? How?

Yes, by specifying multiple cache names in the 'value' or 'cacheNames' attribute as an array, e.g., @CacheEvict(value = {"cache1", "cache2"}).

What happens if you set allEntries = true in @CacheEvict?

A All entries in the specified cache are removed

B The cache entries are refreshed automatically

C The cache is disabled permanently

D Only the cache entry related to the method key is removed

Setting allEntries = true removes all entries from the cache, not just the one related to the method key.

When does cache eviction occur by default with @CacheEvict?

A Before the annotated method runs

B Only if the method throws an exception

C After the annotated method completes successfully

D Immediately when the application starts

By default, cache eviction happens after the annotated method completes successfully.

How do you specify multiple caches to evict in @CacheEvict?

A You cannot evict multiple caches at once

B Use multiple @CacheEvict annotations

C Use the cacheNames attribute with a single string

D Pass an array of cache names to the value attribute

You can specify multiple caches by passing an array of cache names to the value or cacheNames attribute.

What does setting beforeInvocation = true do in @CacheEvict?

A Evicts cache entries before the method runs

B Evicts cache entries after the method runs

C Prevents cache eviction

D Evicts cache only if the method throws an exception

Setting beforeInvocation = true causes cache eviction to happen before the annotated method runs.

Which attribute in @CacheEvict defines the cache to clear?

A key

B value or cacheNames

C condition

D sync

The value or cacheNames attribute specifies which cache(s) to evict entries from.

Describe how @CacheEvict helps keep cache data fresh in a Spring Boot application.

Think about when and why you want to clear cache entries.

Explain the difference between evicting cache before vs after method execution using @CacheEvict.

Consider what happens if the method fails or throws an error.

Practice

1. What is the primary purpose of the @CacheEvict annotation in Spring Boot?

easy

A. To remove or invalidate cache entries after data changes

B. To add new entries to the cache

C. To configure cache storage location

D. To read data from the cache without modification

Solution

1. Step 1: Understand cache behavior

   Cache stores data to speed up repeated access, but stale data can cause issues.

2. Step 2: Role of @CacheEvict

   @CacheEvict is used to remove outdated cache entries after data changes to keep cache fresh.

3. Final Answer:

   To remove or invalidate cache entries after data changes -> Option A

4. Quick Check:

   @CacheEvict removes cache entries [OK]

Hint: Remember: @CacheEvict clears cache after updates [OK]

Common Mistakes:

• Confusing @CacheEvict with @CachePut or @Cacheable
• Thinking it adds cache entries instead of removing
• Assuming it configures cache storage

2. Which of the following is the correct way to use @CacheEvict to clear a cache named "users" after a method executes?

easy

A. @CacheEvict(cacheNames = "users", allEntries = true)

B. @CacheEvict(cacheName = "users", clearAll = true)

C. @CacheEvict(value = "users", removeAll = true)

D. @CacheEvict(cache = "users", evictAll = true)

Solution

1. Step 1: Identify correct attribute names

   The correct attribute to specify cache names is cacheNames or value. To clear all entries, use allEntries = true.

2. Step 2: Match correct syntax

   @CacheEvict(cacheNames = "users", allEntries = true) uses @CacheEvict(cacheNames = "users", allEntries = true), which is valid syntax.

3. Final Answer:

   @CacheEvict(cacheNames = "users", allEntries = true) -> Option A

4. Quick Check:

   cacheNames + allEntries = true [OK]

Hint: Use cacheNames and allEntries=true to clear all cache keys [OK]

Common Mistakes:

• Using wrong attribute names like cacheName or cache
• Confusing allEntries with clearAll or removeAll
• Missing quotes around cache name

3. Consider this method in a Spring Boot service:

@CacheEvict(cacheNames = "products", key = "#id")
public void deleteProduct(Long id) {
    productRepository.deleteById(id);
}

What happens when deleteProduct(5L) is called?

medium

A. All entries in 'products' cache are removed

B. The cache entry with key 5 in 'products' cache is removed

C. A new cache entry with key 5 is added

D. The method throws a runtime error due to missing key

Solution

1. Step 1: Analyze @CacheEvict usage

   The annotation specifies cacheNames = "products" and key = "#id", so it targets the cache entry with the given id.

2. Step 2: Effect of calling deleteProduct(5L)

   Calling with id 5 removes the cache entry with key 5 from the 'products' cache.

3. Final Answer:

   The cache entry with key 5 in 'products' cache is removed -> Option B

4. Quick Check:

   @CacheEvict with key removes specific cache entry [OK]

Hint: Key in @CacheEvict targets specific cache entry [OK]

Common Mistakes:

• Assuming all cache entries are removed without allEntries=true
• Thinking it adds cache entries instead of removing
• Believing missing key causes runtime error

4. Given this method:

@CacheEvict(cacheNames = "orders", key = "#order.id")
public void cancelOrder(Order order) {
    orderRepository.delete(order);
}

Why might the cache eviction not work as expected?

medium

A. The key expression should be #orderId instead of #order.id

B. The method parameter 'order' is not accessible in SpEL key expression

C. The key expression #order.id requires the 'order' object to be non-null and have a valid id

D. @CacheEvict cannot use complex key expressions

Solution

1. Step 1: Understand SpEL key expression

   The key expression #order.id accesses the id property of the 'order' parameter. This requires 'order' to be non-null and have a valid id.

2. Step 2: Identify why eviction might fail

   If 'order' is null or its id is null, the cache key cannot be resolved, so eviction won't work as expected.

3. Final Answer:

   The key expression #order.id requires the 'order' object to be non-null and have a valid id -> Option C

4. Quick Check:

   SpEL key needs valid object and property [OK]

Hint: Ensure key objects are non-null with valid properties [OK]

Common Mistakes:

• Assuming key expressions cannot use object properties
• Using wrong parameter names in key expression
• Believing @CacheEvict cannot handle complex keys

5. You have a Spring Boot service with two caches: "users" and "sessions". You want to clear all entries in "sessions" cache whenever a user is deleted, but keep "users" cache intact. Which @CacheEvict usage correctly achieves this in the deleteUser method?

public void deleteUser(Long userId) {
    userRepository.deleteById(userId);
    // cache eviction here
}

hard

A. @CacheEvict(cacheNames = "sessions", key = "#userId") on deleteUser method

B. @CacheEvict(cacheNames = {"users", "sessions"}, allEntries = true) on deleteUser method

C. @CacheEvict(cacheNames = "users", key = "#userId") on deleteUser method

D. @CacheEvict(cacheNames = "sessions", allEntries = true) on deleteUser method

Solution

1. Step 1: Understand requirement

   We want to clear all entries in "sessions" cache only, not affect "users" cache.

2. Step 2: Analyze options

   @CacheEvict(cacheNames = "sessions", allEntries = true) on deleteUser method clears all entries in "sessions" cache, matching requirement. @CacheEvict(cacheNames = {"users", "sessions"}, allEntries = true) on deleteUser method clears both caches, which is incorrect. @CacheEvict(cacheNames = "users", key = "#userId") on deleteUser method clears only one user key in "users" cache, not sessions. @CacheEvict(cacheNames = "sessions", key = "#userId") on deleteUser method clears one key in "sessions" cache, not all.

3. Final Answer:

   @CacheEvict(cacheNames = "sessions", allEntries = true) on deleteUser method -> Option D

4. Quick Check:

   allEntries=true clears entire cache [OK]

Hint: Use allEntries=true on target cache to clear all keys [OK]

Common Mistakes:

• Clearing wrong cache or multiple caches unintentionally
• Using key instead of allEntries to clear entire cache
• Assuming deleting user clears user cache automatically