AEM Caching with Google Guava: Use Case, Importance, and Implementation

Caching is essential in optimizing the performance of web applications, and when it comes to Adobe Experience Manager (AEM), caching strategies can be implemented at various levels. One such powerful caching mechanism that developers can use within the AEM application itself is Google Guava caching. In this blog, we will explore why Google Guava caching is important, and how you can use it effectively in AEM, along with a practical use case.

Why Caching Is Important in AEM

AEM is a robust content management system, but its performance can be affected if multiple repetitive and expensive operations (like API calls, database queries, or service executions) are executed frequently. These operations increase the load on the AEM instances, reduce response times, and impact the user experience.

Caching helps avoid redundant processing by storing reusable results and serving them quickly from memory instead of recalculating or re-fetching data. This is especially useful in scenarios such as:

• Frequently accessed data like product catalogs.
• Repeated API calls to external systems.
• Expensive computations or database queries.

Without caching, the overhead of such operations increases the load on the server and negatively impacts the scalability and speed of your application.

Why Use Google Guava Caching?

Google Guava caching is a lightweight, in-memory caching library that provides fine-grained control over caching. Unlike external cache stores like Redis or Memcached, Guava is entirely local to the JVM and is perfect for scenarios where you need fast access to cached data without the complexity of setting up external systems.

Key Benefits of Google Guava Caching:

• Thread-safety: Guava caches are built to be thread-safe, making them ideal for use in multi-threaded environments like AEM.
• Customization: You can configure cache eviction strategies, time-to-live (TTL), and maximum cache sizes.
• Fine-grained control: Guava caches allow you to cache individual objects or service responses instead of caching entire pages or components like a dispatcher cache.

Use Case: Caching Expensive Service Results in AEM

Consider a scenario where your AEM application frequently interacts with an external service to retrieve product details. The external service call is expensive, both in terms of time and resources, and the data doesn't change often. To improve performance, you can cache the results of the service call using Google Guava and serve the cached data on subsequent requests.

Steps for Implementation:

1. Create the Service to Fetch Data: Assume you have a service in AEM that calls an external API to get product details.

   public class ProductService {
       public String getProductDetails(String productId) {
           // Simulate expensive service call
           return externalApiCall(productId);  // Fetch product details from an API
       }
   }

2. Add Google Guava Cache to Store Results: Use Guava’s CacheBuilder to cache the product details for a specified duration.

   import com.google.common.cache.Cache;
   import com.google.common.cache.CacheBuilder;
   
   public class CachingProductService {
       private final ProductService productService;
       private final Cache<String, String> productCache;
   
       public CachingProductService(ProductService productService) {
           this.productService = productService;
           this.productCache = CacheBuilder.newBuilder()
               .expireAfterWrite(15, TimeUnit.MINUTES)  // Cache expires after 15 minutes
               .maximumSize(1000)  // Limit cache size to 1000 entries
               .build();
       }
   
       public String getCachedProductDetails(String productId) {
           try {
               // Retrieve from cache, or load from service if not present
               return productCache.get(productId, () -> productService.getProductDetails(productId));
           } catch (ExecutionException e) {
               e.printStackTrace();
               return null;
           }
       }
   }

3. Usage in AEM Sling Models or Services: When using this service in your Sling models or AEM components, you can now serve cached data instead of making repeated API calls.

   @Model(adaptables = Resource.class)
   public class ProductModel {
       @Inject
       private CachingProductService cachingProductService;
   
       @Inject
       @Optional
       private String productId;
   
       public String getProductDetails() {
           return cachingProductService.getCachedProductDetails(productId);
       }
   }

4. Invalidating Cache: Suppose the product details change before the cache expiration (15 minutes). You can invalidate the specific cache entry:

   public void invalidateProductCache(String productId) {
       productCache.invalidate(productId);  // Invalidate cache entry for a specific product
   }

When to Use Google Guava Caching

While Google Guava caching is powerful and fast, it’s not suitable for every scenario. Here are some use cases where Guava caching shines:

• Backend service caching: Cache data from expensive services or API results.
• Non-persistent data: Use it when you don’t need persistence between application restarts (since Guava caches are in-memory).
• Small datasets: Guava is ideal for caching small datasets (e.g., a few thousand entries) since it's in-memory and local to the JVM.

Drawbacks of Google Guava Caching

Though powerful, Guava caching does have some limitations:

• Limited to JVM memory: Guava caches consume heap memory, so you need to be mindful of memory constraints.
• Not shared across instances: In a multi-instance setup (e.g., multiple publish nodes), each instance will maintain its own cache. Changes in one instance won’t invalidate the cache in others unless explicitly handled.
• No persistence: The cache is non-persistent, meaning it will be lost when the application restarts.

Dispatcher Caching vs. Google Guava Caching

While Dispatcher caching in AEM is used for full-page or component-level caching at the CDN/web server level, Google Guava caching is focused on fine-grained, in-memory data caching.

• Dispatcher caching: Best for static content or full pages that don’t change frequently.
• Guava caching: Ideal for backend services, API results, or dynamic data that can be fetched once and reused multiple times.

You can also combine both approaches:

• Use Dispatcher to cache static content or responses for anonymous users.
• Use Guava to cache frequently accessed backend data, reducing the need for repetitive service calls.

Conclusion

Google Guava caching is a powerful tool to improve the performance of your AEM applications by reducing the load on expensive backend services or computations. It provides developers with fine-grained control over how and when to cache data, making it suitable for dynamic and frequently accessed data in AEM.

By implementing a thoughtful caching strategy using both Guava caching and Dispatcher caching, you can significantly enhance the performance and scalability of your AEM environment.

Further Reading

• Google Guava Caching Documentation
• Adobe Experience Manager Dispatcher