@CacheEvict for invalidation in Spring Boot

Introduction

@CacheEvict helps remove old or unwanted data from the cache. This keeps your app's data fresh and correct.

When you update or delete data and want to remove the old cached version.

When you want to clear all cached data after a big change.

When you want to remove cache for a specific key after a method runs.

When you want to avoid showing outdated information to users.

Syntax

Spring Boot

@CacheEvict(value = "cacheName", key = "#key", allEntries = false, beforeInvocation = false)

value is the name of the cache to clear.

key defines which cache entry to remove. Use SpEL (Spring Expression Language) to specify keys.

Examples

Removes the cache entry for the book with the given id.

Spring Boot

@CacheEvict(value = "books", key = "#id")
public void removeBook(Long id) { ... }

Clears all entries in the 'books' cache.

Spring Boot

@CacheEvict(value = "books", allEntries = true)
public void clearAllBooksCache() { ... }

Evicts cache before the method runs, useful if method might throw exceptions.

Spring Boot

@CacheEvict(value = "books", key = "#book.id", beforeInvocation = true)
public void deleteBook(Book book) { ... }

Sample Program

This service caches book names by id. When a book is updated, its cache entry is removed. You can also clear all cached books.

Spring Boot

import org.springframework.cache.annotation.CacheEvict;
import org.springframework.cache.annotation.Cacheable;
import org.springframework.stereotype.Service;

@Service
public class BookService {

    @Cacheable(value = "books", key = "#id")
    public String getBook(Long id) {
        // Simulate fetching book from database
        return "Book" + id;
    }

    @CacheEvict(value = "books", key = "#id")
    public void updateBook(Long id, String newName) {
        // Simulate updating book in database
        System.out.println("Updated book " + id + " to " + newName);
    }

    @CacheEvict(value = "books", allEntries = true)
    public void clearCache() {
        System.out.println("Cleared all books cache");
    }
}

Important Notes

Use allEntries=true carefully; it clears the whole cache which might affect performance.

beforeInvocation=true evicts cache before method runs, useful if method might fail.

Cache keys use Spring Expression Language (SpEL) to pick which cache entry to remove.

Summary

@CacheEvict removes cache entries to keep data fresh.

Use it after data changes to avoid stale cache.

You can remove specific keys or clear entire caches.

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