@CacheEvict for invalidation in Spring Boot - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to evict the cache named 'books' after the method runs.

Spring Boot

@CacheEvict(cacheNames = "[1]")
public void clearCache() {
    // method body
}

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

Ausers

Bproducts

Corders

Dbooks

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong cache name that does not exist.

Forgetting to specify the cache name.

The @CacheEvict annotation uses the cacheNames attribute to specify which cache to clear. Here, 'books' is the correct cache name to evict.

2fill in blank

medium

Complete the code to evict all entries in the 'books' cache after the method runs.

Spring Boot

@CacheEvict(cacheNames = "books", [1] = true)
public void clearAllBooksCache() {
    // method body
}

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

AallEntries

Bkey

Ccondition

DbeforeInvocation

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'key' instead of 'allEntries' to clear all cache entries.

Not setting the attribute to true.

The allEntries attribute set to true tells Spring to evict all entries in the specified cache.

3fill in blank

hard

Fix the error in the code to evict the cache entry with key '123' from the 'books' cache.

Spring Boot

@CacheEvict(cacheNames = "books", key = "[1]")
public void evictBook() {
    // method body
}

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

A123

B'123'

C"123"

Dkey

Attempts:

3 left

💡 Hint

Common Mistakes

Using a number without quotes as key.

Using double quotes inside double quotes without escaping.

The key attribute requires a SpEL expression as a string. The key '123' must be enclosed in single quotes inside the double quotes.

4fill in blank

hard

Fill both blanks to evict the cache entry with key 'id' before the method runs.

Spring Boot

@CacheEvict(cacheNames = "books", key = "[1]", [2] = true)
public void evictBefore(Long id) {
    // method body
}

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

A#id

Bfalse

CbeforeInvocation

Dtrue

Attempts:

3 left

💡 Hint

Common Mistakes

Using the parameter name without '#' in key.

Not setting beforeInvocation to true.

The key should be #id to refer to the method parameter. The beforeInvocation attribute set to true evicts the cache before the method runs.

5fill in blank

hard

Fill all three blanks to evict the cache entry with key 'user.id' only if the user's status is 'inactive'.

Spring Boot

@CacheEvict(cacheNames = "users", key = "[1]", condition = "[2] == 'inactive'", [3] = false)
public void evictInactiveUser(User user) {
    // method body
}

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

A#user.id

B#user.status

CbeforeInvocation

DallEntries

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong SpEL expressions for key or condition.

Confusing beforeInvocation with allEntries.

The key uses #user.id to access the user's id. The condition checks if #user.status equals 'inactive'. The beforeInvocation attribute set to false means eviction happens after method runs.

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