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Aedile

Aedile is a simple Kotlin wrapper for Caffeine which prefers coroutines rather than Java futures.

See changelog

Features

Suspendable functions: Rather than use Java's CompletableFutures, all operations on Aedile are suspendable and executed in their own coroutines.
Backed by Caffeine: This is not a new cache implementation with its own bugs and quirks, but a simple wrapper around Caffeine which has been used on the JVM for years.
Kotlin durations: Specify expiration and refresh times in kotlin.time.Duration rather than Java durations.
Kotlin functions: Wherever a function is required - eg eviction listener - Aedile supports Kotlin functions rather than Java's Function interface.

Usage

Add Aedile to your build:

implementation 'com.sksamuel.aedile:aedile-core:<version>'

Next, in your code, create a cache configuration using the standard Caffeine builder. Then, instead of using the buildAsync methods that Caffeine provides, use the asCache or asLoadingCache methods that Aedile provides.

val cache = Caffeine.newBuilder().asCache<String, String>()

With this cache we can request values if present, or supply a suspendable function to compute them.

val value1 = cache.getIfPresent("foo") // value or null

val value2 = cache.get("foo") {
   delay(100) // look ma, we support suspendable functions!
   "value"
}

The asLoadingCache method supports a generic compute function which is used if no specific compute function is provided.

val cache = Caffeine.newBuilder().asLoadingCache<String, String>() {
   delay(1) // look ma, we support suspendable functions!
   "value"
}

cache.get("foo") // uses default compute, will return "value"
cache.get("bar") { "other" } // uses specific compute function to return "other"

Configuration

When creating the cache, Aedile wraps the standard Caffeine configuration options, adding extension functions to make it easier to use Kotlin types - such as kotlin.time.Duration rather than Java's Duration.

For example:

val cache = Caffeine
   .newBuilder()
   .expireAfterWrite(1.hours) // supports kotlin.time.Duration
   .maximumSize(100) // standard Caffeine option
   .asCache<String, String>()

Evictions

Caffeine provides different approaches to eviction:

expireAfterAccess(duration): Expire entries after the specified duration has passed since the entry was last accessed by a read or write. This could be desirable if the cached data is bound to a session and expires due to inactivity.
expireAfterWrite(duration): Expire entries after the specified duration has passed since the entry was created, or the most recent replacement of the value. This could be desirable if cached data grows stale after a certain amount of time.
expireAfter(expiry): Pass an implementation of Expiry which has methods for specifying that expiry should occur either after a duration from insert, a duration from last refresh, or a duration from last read.
invalidate / invalidateAll: Programatically remove entries based on their key(s) or remove all entries. In the case of a loading cache, any currently loading values may not be removed.

You can specify a suspendable function to listen to evictions using the withEvictionListener method.

val cache = Caffeine
   .newBuilder()
   .expireAfterWrite(1.hours) // supports kotlin.time.Duration
   .maximumSize(100) // standard Caffeine option
   .asCache<String, String>()
   .withEvictionListener { key, value, cause ->
      when (cause) {
         RemovalCause.SIZE -> println("Removed due to size constraints")
         else -> delay(100) // suspendable for no real reason, but just to show you can!!
      }
   }.asCache<String, String>()

Removals

Similar to evictions, you can specify a suspendable function to listen to removals using the withRemovalListener method.

val cache = Caffeine
   .newBuilder()
   .asCache<String, String>()
   .withRemovalListener { key, value, cause ->
      ...
   }.asCache<String, String>()

Coroutine Context

Aedile will use the context from the calling function for executing the compute functions. You can specify your own context by just switching the context like with any suspendable call.

val cache = Caffeine.newBuilder().asCache<String, String>()
val value = cache.get("foo") {
   withContext(Dispatchers.IO) {
      // blocking database call
   }
}
}

Metrics

Micrometer provides integration which wraps the Caffeine cache classes. To use this, call .underlying() to get access to the wrapped Caffeine instance.

For example:

CaffeineCacheMetrics(cache.underlying().synchronous(), "my-cache-name", tags).bindTo(registry)