How do you handle cache eviction with the @CacheEvict annotation?

Table of Contents

• Introduction
  • 1. What Does the **@CacheEvict** Annotation Do?
  • 2. Basic Usage of **@CacheEvict**
    • Example: Evicting a Specific Cache Entry
  • 3. Evicting All Cache Entries
    • Example: Evicting All Entries from a Cache
  • 4. Conditional Cache Eviction
    • Example: Conditional Eviction Based on a Method Parameter
  • 5. Evicting Cache Before or After Method Execution
    • Example: Evict Cache Before Method Execution
  • 6. Practical Examples of Using **@CacheEvict**
    • Example 1: Cache Eviction After Updating an Entity
    • Example 2: Cache Eviction After a Bulk Operation
  • 7. Cache Eviction with Multiple Caches
    • Example: Evicting from Multiple Caches
• Conclusion

Introduction

In caching systems, eviction refers to the process of removing cache entries when they are no longer needed or are outdated. Cache eviction plays a vital role in ensuring that stale data doesn't remain in the cache, and that the cache size is optimized to avoid excessive memory usage.

In Spring Boot, the @CacheEvict annotation is used to handle the eviction of cache entries. This annotation allows you to explicitly remove data from the cache after certain operations, such as updating or deleting an entity, ensuring that your cache stays synchronized with the underlying data.

In this guide, we'll explore how to handle cache eviction in Spring Boot using the @CacheEvict annotation, including different strategies for clearing cache entries based on your application’s requirements.

1. What Does the **@CacheEvict** Annotation Do?

The @CacheEvict annotation is used to evict (remove) entries from a cache. It can be applied to methods that modify or delete data so that the cache is updated or cleared when the underlying data changes.

The @CacheEvict annotation supports several options, such as:

• evicting specific cache entries based on the cache key
• evicting all entries from a cache
• conditional eviction based on specific criteria
• before or after method execution

By using @CacheEvict, you can ensure that the cache always reflects the most up-to-date state of your data, especially when performing operations that modify the data, like creating, updating, or deleting records.

2. Basic Usage of **@CacheEvict**

The most basic use of @CacheEvict is to remove an entry from the cache. You can specify the cache name and the key for the entry that needs to be evicted.

Example: Evicting a Specific Cache Entry

In this example:

• @CacheEvict(value = "products", key = "#id"): This tells Spring to evict the cache entry with the key equal to the id of the product from the cache named "products".

This is useful when you want to ensure that the cache is cleared whenever a product is deleted, preventing stale data from being returned on future requests.

3. Evicting All Cache Entries

You can also clear all entries within a cache. This is useful when the entire cache needs to be refreshed or invalidated.

Example: Evicting All Entries from a Cache

In this example:

• @CacheEvict(value = "products", allEntries = true): This will remove all entries from the cache named "products". It’s useful when the entire cache becomes invalidated, for instance, after a bulk update or a significant change in the underlying data.

4. Conditional Cache Eviction

You can conditionally evict cache entries based on certain conditions. The condition attribute in the @CacheEvict annotation allows you to define a condition using Spring Expression Language (SpEL).

Example: Conditional Eviction Based on a Method Parameter

In this example:

• @CacheEvict(value = "products", key = "#id", condition = "#id > 100"): This will evict the cache entry only if the id is greater than 100. The condition uses SpEL to evaluate whether to evict the cache.

This allows for more fine-grained control over when cache eviction should happen.

5. Evicting Cache Before or After Method Execution

You can control whether the cache is evicted before or after the method execution. By default, @CacheEvict performs the eviction after the method has executed. However, you can change this behavior by setting the beforeInvocation attribute to true.

Example: Evict Cache Before Method Execution

In this example:

• @CacheEvict(value = "products", key = "#id", beforeInvocation = true): This will evict the cache entry before the updateProduct method is executed. This is useful when you want to ensure that the cache is cleared before the actual method logic runs, ensuring that stale cache data doesn’t persist during the method execution.

6. Practical Examples of Using **@CacheEvict**

Example 1: Cache Eviction After Updating an Entity

When updating an entity, it’s crucial to ensure that the cache reflects the updated data.

In this example:

• After the product is updated, the cache entry associated with the product’s id is evicted, ensuring that the cache is not serving outdated data.

Example 2: Cache Eviction After a Bulk Operation

If you are performing a bulk operation, such as clearing all products or updating a large set of products, you may want to clear the entire cache.

In this example:

• The entire cache is cleared after the bulk operation. This ensures that the cache is synchronized with the new data after the update.

7. Cache Eviction with Multiple Caches

In some cases, you may want to evict entries from multiple caches simultaneously. You can achieve this by specifying multiple cache names in the value parameter.

Example: Evicting from Multiple Caches

In this example:

• The product entry will be evicted from both "products" and "productDetails" caches, ensuring that all caches containing the product data are cleared.

Conclusion

The @CacheEvict annotation in Spring Boot is a powerful tool for managing cache eviction. Whether you need to clear specific cache entries, evict all entries in a cache, or perform conditional or pre-method eviction, @CacheEvict provides the flexibility to keep your cache in sync with the underlying data. By strategically evicting cache entries after data changes, you can ensure that your application always serves fresh and accurate data, optimizing both performance and consistency.