@CachePut for updating cache in Spring Boot - Step-by-Step Execution

Concept Flow - @CachePut for updating cache

Method call with @CachePut

↓

Method executes and returns value

↓

Cache updated with new value

↓

Return updated value to caller

When a method annotated with @CachePut is called, it runs the method and updates the cache with the returned value before returning it.

Execution Sample

Spring Boot

@CachePut(value = "users", key = "#user.id")
public User updateUser(User user) {
    // update user in DB
    return user;
}

This method updates a user and refreshes the cache entry for that user.

Execution Table

Step	Action	Input	Cache Before	Cache Update	Return Value
1	Call updateUser with user{id=1, name='Alice'}	user{id=1, name='Alice'}	{}	{}	pending
2	Execute method: update DB and return user	user{id=1, name='Alice'}	{}	{}	user{id=1, name='Alice'}
3	Update cache 'users' with key=1	user{id=1, name='Alice'}	{}	{1: user{id=1, name='Alice'}}	user{id=1, name='Alice'}
4	Return updated user	user{id=1, name='Alice'}	{1: user{id=1, name='Alice'}}	{1: user{id=1, name='Alice'}}	user{id=1, name='Alice'}
5	Call updateUser with user{id=1, name='Alice Smith'}	user{id=1, name='Alice Smith'}	{1: user{id=1, name='Alice'}}	{1: user{id=1, name='Alice'}}	pending
6	Execute method: update DB and return user	user{id=1, name='Alice Smith'}	{1: user{id=1, name='Alice'}}	{1: user{id=1, name='Alice'}}	user{id=1, name='Alice Smith'}
7	Update cache 'users' with key=1	user{id=1, name='Alice Smith'}	{1: user{id=1, name='Alice'}}	{1: user{id=1, name='Alice Smith'}}	user{id=1, name='Alice Smith'}
8	Return updated user	user{id=1, name='Alice Smith'}	{1: user{id=1, name='Alice Smith'}}	{1: user{id=1, name='Alice Smith'}}	user{id=1, name='Alice Smith'}
9	Call updateUser with user{id=2, name='Bob'}	user{id=2, name='Bob'}	{1: user{id=1, name='Alice Smith'}}	{1: user{id=1, name='Alice Smith'}}	pending
10	Execute method: update DB and return user	user{id=2, name='Bob'}	{1: user{id=1, name='Alice Smith'}}	{1: user{id=1, name='Alice Smith'}}	user{id=2, name='Bob'}
11	Update cache 'users' with key=2	user{id=2, name='Bob'}	{1: user{id=1, name='Alice Smith'}}	{1: user{id=1, name='Alice Smith'}, 2: user{id=2, name='Bob'}}	user{id=2, name='Bob'}
12	Return updated user	user{id=2, name='Bob'}	{1: user{id=1, name='Alice Smith'}, 2: user{id=2, name='Bob'}}	{1: user{id=1, name='Alice Smith'}, 2: user{id=2, name='Bob'}}	user{id=2, name='Bob'}
13	No more calls	-	{1: user{id=1, name='Alice Smith'}, 2: user{id=2, name='Bob'}}	{1: user{id=1, name='Alice Smith'}, 2: user{id=2, name='Bob'}}	-

💡 No more method calls; cache holds latest updated users.

Variable Tracker

Variable	Start	After Step 3	After Step 7	After Step 11	Final
cache 'users'	{}	{1: user{id=1, name='Alice'}}	{1: user{id=1, name='Alice Smith'}}	{1: user{id=1, name='Alice Smith'}, 2: user{id=2, name='Bob'}}	{1: user{id=1, name='Alice Smith'}, 2: user{id=2, name='Bob'}}
return value	N/A	user{id=1, name='Alice'}	user{id=1, name='Alice Smith'}	user{id=2, name='Bob'}	user{id=2, name='Bob'}

Key Moments - 2 Insights

Why does the cache update even if the method is called multiple times with the same key?

Because @CachePut always runs the method and updates the cache with the returned value, as shown in steps 3 and 7 where the cache entry for key=1 is replaced.

Does @CachePut skip method execution if the cache already has the key?

No, @CachePut always executes the method and then updates the cache, unlike @Cacheable which may skip execution if cache hit occurs. This is clear in steps 5-8.

Visual Quiz - 3 Questions

Look at the execution table at step 7. What is the cache content after updating user with id=1?

A {1: user{id=1, name='Alice Smith'}}

B {1: user{id=1, name='Alice'}}

C {}

D {2: user{id=2, name='Bob'}}

💡 Hint

Check the 'Cache Update' column at step 7 in the execution table.

At which step does the cache first get a new entry for user id=2?

A Step 9

B Step 11

C Step 10

D Step 12

💡 Hint

Look for when the cache 'users' key=2 appears in the 'Cache Update' column.

If the method returned a different user object but with the same id, what would happen to the cache?

A Cache would clear all entries

B Cache would keep the old user object

C Cache would update with the new user object for that id

D Cache would throw an error

💡 Hint

Refer to how cache updates at steps 3 and 7 with new user objects for the same key.

Concept Snapshot

@CachePut runs the method every time and updates the cache with the returned value.
Use it to refresh cache entries after updates.
Unlike @Cacheable, it does not skip method execution.
Specify cache name and key to control cache entry.
Cache is updated after method returns.

Full Transcript

When you use @CachePut on a method, every time you call that method, it runs fully and then updates the cache with the result. For example, if you update a user, the method saves the user to the database and then puts the updated user into the cache under the user's id. This means the cache always has the latest data after the method runs. Unlike @Cacheable, which can skip running the method if the cache already has data, @CachePut always runs the method and refreshes the cache. This is useful when you want to keep the cache in sync after changes. The cache key is usually the id or unique identifier of the data. So, calling updateUser with a changed user will replace the old cached user with the new one. This way, your cache stays fresh and your app uses the latest data.

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