@CachePut for updating cache in Spring Boot - Cheat Sheet & Quick Revision

Recall & Review

beginner

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

The @CachePut annotation updates the cache with the method's result every time the method is called, without skipping the method execution.

beginner

How does @CachePut differ from @Cacheable in Spring Boot caching?

@Cacheable skips method execution if the cache has the value, while @CachePut always executes the method and updates the cache with the new result.

beginner

Which attribute of @CachePut specifies the cache name to update?

The 'value' or 'cacheNames' attribute specifies the cache name where the result will be stored or updated.

intermediate

Can @CachePut be used to update multiple caches at once?

Yes, by specifying multiple cache names in the 'value' or 'cacheNames' attribute as an array, @CachePut can update multiple caches simultaneously.

intermediate

Why is @CachePut useful when updating data in a database?

Because it ensures the cache is updated with the latest data after a database update, keeping cache and database in sync without skipping method execution.

What happens when a method annotated with @CachePut is called?

A The method executes and the cache is updated with the result.

B The method is skipped if cache has the value.

C The cache is cleared before method execution.

D The cache is never updated.

@CachePut always executes the method and updates the cache with the new result.

Which attribute do you use to specify the cache name in @CachePut?

A cacheKey

B cacheName

C value

D cacheStore

The 'value' or 'cacheNames' attribute specifies the cache name in @CachePut.

Can @CachePut be used to update the cache without executing the method?

A Yes, it skips method execution.

B Only with a special flag.

C Only if cache is empty.

D No, it always executes the method.

@CachePut always executes the method and then updates the cache.

Why might you choose @CachePut over @Cacheable when updating data?

A To update cache with fresh data after changes.

B To avoid method execution.

C To clear the cache.

D To disable caching.

@CachePut updates the cache with fresh data after method execution, useful when data changes.

How do you update multiple caches with @CachePut?

A Use multiple @CachePut annotations.

B Specify multiple cache names in the 'value' attribute as an array.

C Call the method multiple times.

D It is not possible.

You can specify multiple cache names in the 'value' or 'cacheNames' attribute as an array.

Explain how @CachePut works and when you would use it in a Spring Boot application.

Think about keeping cache and database data in sync.

Describe the difference between @CachePut and @Cacheable annotations in Spring Boot caching.

Focus on method execution and cache update differences.

Practice

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

easy

A. To update the cache with the method's return value after execution

B. To clear all entries in the cache before method execution

C. To cache the method result only if it is not already cached

D. To disable caching for the annotated method

Solution

1. Step 1: Understand the role of @CachePut

   @CachePut is used to update the cache with fresh data after the method runs, unlike @Cacheable which caches only if data is absent.

2. Step 2: Compare options with @CachePut behavior

   Only To update the cache with the method's return value after execution correctly describes updating the cache after method execution. Others describe different caching behaviors.

3. Final Answer:

   To update the cache with the method's return value after execution -> Option A

4. Quick Check:

   @CachePut updates cache after method runs [OK]

Hint: Remember: @CachePut always updates cache after method runs [OK]

Common Mistakes:

• Confusing @CachePut with @Cacheable
• Thinking @CachePut clears cache
• Assuming it caches only if absent

2. Which of the following is the correct syntax to use @CachePut to update a cache named "users" with a key based on the method parameter id?

easy

A. @CachePut(cacheName = "users", key = "id")

B. @CachePut(value = "users", key = "#id")

C. @CachePut(name = "users", key = "id")

D. @CachePut(cache = "users", key = "#id")

Solution

1. Step 1: Recall correct attribute names for @CachePut

   The correct attribute for cache name is 'value' or 'cacheNames', and SpEL expressions for keys use '#'.

2. Step 2: Analyze each option's syntax

   @CachePut(value = "users", key = "#id") uses 'value' and '#id' correctly. Others use incorrect attribute names or miss the '#' for SpEL.

3. Final Answer:

   @CachePut(value = "users", key = "#id") -> Option B

4. Quick Check:

   Use 'value' and '#param' for key in @CachePut [OK]

Hint: Use 'value' for cache name and '#' before param in key [OK]

Common Mistakes:

• Using wrong attribute names like cacheName or cache
• Missing '#' in key expression
• Using plain string instead of SpEL for key

3. Given the following method in a Spring Boot service:

@CachePut(value = "products", key = "#product.id")
public Product updateProduct(Product product) {
    product.setPrice(product.getPrice() + 10);
    return product;
}

What will be the effect on the cache when this method is called with a product having id=5 and price=100?

medium

A. The cache is not affected because @CachePut only caches if absent

B. The cache entry with key 5 is removed from the cache

C. The cache entry with key 5 is updated with the product having price 110

D. A new cache entry with key 110 is added

Solution

1. Step 1: Understand @CachePut behavior on method call

   @CachePut updates the cache entry with the key specified after the method returns the updated object.

2. Step 2: Analyze the method logic and cache key

   The method increases price by 10 and returns the product. The key is product.id which is 5, so cache key 5 is updated with product price 110.

3. Final Answer:

   The cache entry with key 5 is updated with the product having price 110 -> Option C

4. Quick Check:

   @CachePut updates cache key with returned value [OK]

Hint: Returned value updates cache at key specified [OK]

Common Mistakes:

• Thinking cache key changes to price
• Assuming cache entry is removed
• Confusing @CachePut with @Cacheable

4. Consider this method annotated with @CachePut:

@CachePut(value = "orders", key = "#order.id")
public Order updateOrder(Order order) {
    // missing return statement
}

What is the problem with this code?

medium

A. The method should be annotated with @Cacheable instead

B. The key expression is invalid and causes a syntax error

C. The cache name 'orders' is not allowed in @CachePut

D. The method does not return a value, so cache cannot be updated

Solution

1. Step 1: Check method return requirement for @CachePut

   @CachePut requires the method to return a value to update the cache with that value.

2. Step 2: Identify missing return statement issue

   The method lacks a return statement, so no value is returned to update the cache, causing runtime issues.

3. Final Answer:

   The method does not return a value, so cache cannot be updated -> Option D

4. Quick Check:

   @CachePut needs method return to update cache [OK]

Hint: Always return updated value when using @CachePut [OK]

Common Mistakes:

• Forgetting to return the updated object
• Confusing cache name attribute
• Using @Cacheable instead of @CachePut incorrectly

5. You have a method that updates a user's email and you want to ensure the cache entry for that user is updated immediately after the change. Which approach correctly uses @CachePut to achieve this, assuming the method signature is public User updateEmail(Long userId, String newEmail)?

hard

A. @CachePut(value = "users", key = "#userId")
public User updateEmail(Long userId, String newEmail) {
User user = userRepository.findById(userId);
user.setEmail(newEmail);
userRepository.save(user);
return user;
}

B. @CachePut(value = "users", key = "#newEmail")
public User updateEmail(Long userId, String newEmail) {
User user = userRepository.findById(userId);
user.setEmail(newEmail);
userRepository.save(user);
return user;
}

C. @CachePut(value = "users")
public void updateEmail(Long userId, String newEmail) {
User user = userRepository.findById(userId);
user.setEmail(newEmail);
userRepository.save(user);
}

D. @CachePut(key = "#userId")
public User updateEmail(Long userId, String newEmail) {
User user = userRepository.findById(userId);
user.setEmail(newEmail);
userRepository.save(user);
return user;
}

Solution

1. Step 1: Verify correct cache name and key usage

   @CachePut(value = "users", key = "#userId") public User updateEmail(Long userId, String newEmail) { User user = userRepository.findById(userId); user.setEmail(newEmail); userRepository.save(user); return user; } uses 'value = "users"' and key '#userId', correctly identifying the cache and key.

2. Step 2: Check method return and update logic

   @CachePut(value = "users", key = "#userId") public User updateEmail(Long userId, String newEmail) { User user = userRepository.findById(userId); user.setEmail(newEmail); userRepository.save(user); return user; } returns the updated User object, which is necessary for @CachePut to update the cache. Other options either use wrong key, no return, or missing cache name.

3. Final Answer:

   @CachePut(value = "users", key = "#userId") public User updateEmail(Long userId, String newEmail) { User user = userRepository.findById(userId); user.setEmail(newEmail); userRepository.save(user); return user; } -> Option A

4. Quick Check:

   Return updated object and use correct cache name and key [OK]

Hint: Return updated object and use correct cache name and key [OK]

Common Mistakes:

• Using wrong key expression
• Not returning updated object
• Omitting cache name in annotation