How do you implement a custom cache key generator in Spring?

Table of Contents

• Introduction
  • 1. Understanding Spring’s Default Cache Key Generation
  • 2. Creating a Custom Cache Key Generator
    • Example: Custom Cache Key Generator
    • Explanation:
    • Benefits of Custom Key Generation:
  • 3. Configuring Spring to Use the Custom Cache Key Generator
    • Example: Using Custom Key Generator in @Cacheable
    • Example: Using Custom Key Generator with @CachePut
  • 4. Using Custom Cache Key Generator in Multiple Places
  • 5. Practical Examples of Custom Cache Key Generation
    • Example 1: Combining Multiple Parameters into a Single Key
    • Example 2: Using Method Name and User-Specific Data
• Conclusion

Introduction

In Spring applications, caching is often implemented using annotations such as @Cacheable to store and retrieve data from a cache. By default, Spring generates cache keys based on method parameters. However, there are scenarios where you might need more control over the key generation, such as when you want to combine multiple parameters, include specific fields, or create complex keys for better cache partitioning.

To customize this behavior, Spring allows you to define your own cache key generator. This gives you the flexibility to generate cache keys based on your application's unique requirements.

In this guide, we will explore how to implement a custom cache key generator in Spring and how to apply it to your caching setup.

1. Understanding Spring’s Default Cache Key Generation

By default, Spring generates cache keys using a combination of method arguments. The cache key is usually derived by using the SimpleKeyGenerator, which creates a key based on the method’s parameters.

For example:

In this case, the cache key is simply the id parameter. If the method had multiple parameters, Spring would generate a key based on all arguments.

However, this default behavior may not be suitable for every use case, especially in more complex applications. This is where a custom cache key generator comes into play.

2. Creating a Custom Cache Key Generator

To create a custom cache key generator, you need to implement the CacheKeyGenerator interface. The generate method of this interface is responsible for creating the cache key based on the method and its parameters.

Here’s how you can implement a custom key generator:

Example: Custom Cache Key Generator

Explanation:

• The CustomCacheKeyGenerator implements the KeyGenerator interface.
• The generate method is overridden to create a key by combining the method name and its parameters.
• The key is generated by iterating over the params array, appending each parameter value to the key string.
• The final result is a String representing the custom cache key.

Benefits of Custom Key Generation:

• Complex Key Logic: You can combine multiple method parameters, method names, or even external data (like user sessions) into your cache key.
• Consistency: With custom key generation, you can ensure that the cache key format is consistent with your application's needs.

3. Configuring Spring to Use the Custom Cache Key Generator

Once you have created the custom key generator, the next step is to configure Spring to use it.

To do this, you can specify the keyGenerator attribute in the @Cacheable, @CachePut, or @CacheEvict annotations.

Example: Using Custom Key Generator in @Cacheable

• The @Cacheable annotation is used with the keyGenerator attribute, which specifies the name of the custom key generator bean ("customCacheKeyGenerator").
• In this case, the getUserById method’s cache key will be generated by the CustomCacheKeyGenerator bean.

Example: Using Custom Key Generator with @CachePut

In this case, the cache key for the updated user will also be generated using the custom key generator.

4. Using Custom Cache Key Generator in Multiple Places

If you want to use the same custom key generator across multiple caching annotations, you simply reference the generator by its bean name (e.g., "customCacheKeyGenerator") wherever the keyGenerator attribute is applicable.

In both methods (getProductById and deleteProduct), the cache keys will be generated using the CustomCacheKeyGenerator.

5. Practical Examples of Custom Cache Key Generation

Example 1: Combining Multiple Parameters into a Single Key

You might want to create a cache key that combines multiple method parameters for better granularity. For example, when querying a database, you may want to cache results based on both id and region:

This would create cache keys like getProductById:123-UK, allowing you to cache product data separately for each region.

Example 2: Using Method Name and User-Specific Data

In some applications, cache keys might need to include user-specific data. For example, you could generate a cache key that includes the username or session ID:

In this case, the cache key might look like user_john:getUserById:123, ensuring that the cache is partitioned by user.

Conclusion

Implementing a custom cache key generator in Spring allows you to fine-tune how cache keys are created based on your application’s unique requirements. Whether you're combining multiple parameters, including user-specific data, or applying custom logic, this feature gives you full control over your caching mechanism.

To implement a custom cache key generator:

1. Create a class that implements the KeyGenerator interface.
2. Override the generate method to define your custom key generation logic.
3. Configure Spring to use your custom key generator by specifying it in caching annotations like @Cacheable, @CachePut, or @CacheEvict.

By customizing your cache key generation, you can improve the performance and granularity of your caching strategy, making it more aligned with your application’s specific needs.