@CachePut for updating cache in Spring Boot - Performance & Optimization

Performance: @CachePut for updating cache

MEDIUM IMPACT

This affects server response time and memory usage by controlling how cache updates happen during method execution.

Updating cached data after a method changes the underlying data

Spring Boot

@CachePut(value = "items", key = "#item.id")
public Item updateItem(Item item) {
  // update logic
  return item;
}

Forces cache update after method runs, ensuring cache always has fresh data.

📈 Performance GainAvoids stale cache reads and extra DB calls, improving data consistency.

Updating cached data after a method changes the underlying data

Spring Boot

@Cacheable("items")
public Item updateItem(Item item) {
  // update logic
  return item;
}

Using @Cacheable only reads from cache and does not update it after changes, causing stale data.

📉 Performance CostCauses stale cache leading to inconsistent data and potential extra DB calls later.

Performance Comparison

Pattern	Method Execution	Cache Update	Data Freshness	Verdict
@Cacheable only	Skipped if cached	No update	Stale data possible	[X] Bad
@CachePut	Always runs	Updates cache after	Fresh data guaranteed	[OK] Good

Rendering Pipeline

When a method annotated with @CachePut runs, it executes fully and then updates the cache with the returned value. This avoids skipping method execution unlike @Cacheable.

→Method Execution

→Cache Update

⚠️ BottleneckCache Update stage can add latency if cache storage is slow or large data is stored.

Optimization Tips

1Use @CachePut when you need to update cache after method execution.

2Avoid using @CachePut for read-only methods to prevent unnecessary cache updates.

3Monitor cache update latency to keep server response times low.

Performance Quiz - 3 Questions

What is the main performance impact of using @CachePut in Spring Boot?

A It always executes the method and updates the cache, adding some latency.

B It skips method execution if cache exists, improving speed.

C It disables caching completely.

D It only reads from cache without updating.

DevTools: Spring Boot Actuator / Logs

How to check: Enable cache logging or use actuator endpoints to monitor cache hits and updates during method calls.

What to look for: Look for cache update logs confirming @CachePut triggers cache refresh after method execution.

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