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§The Play cache API

Caching data is a typical optimization in modern applications, and so Play provides a global cache. An important point about the cache is that it behaves just like a cache should: the data you just stored may just go missing.

For any data stored in the cache, a regeneration strategy needs to be put in place in case the data goes missing. This philosophy is one of the fundamentals behind Play, and is different from Java EE, where the session is expected to retain values throughout its lifetime.

The default implementation of the cache API uses EHCache.

§Importing the Cache API

Add cache into your dependencies list. For example, in build.sbt:

libraryDependencies ++= Seq(
  cache
)

§Accessing the Cache API

The cache API is provided by the CacheApi object, and can be injected into your component like any other dependency. For example:

import play.cache.*;
import play.mvc.*;

import javax.inject.Inject;

public class Application extends Controller {

    private CacheApi cache;

    @Inject
    public Application(CacheApi cache) {
        this.cache = cache;
    }

    // ...
}

Note: The API is intentionally minimal to allow various implementations to be plugged in. If you need a more specific API, use the one provided by your Cache plugin.

Using this simple API you can store data in the cache:

cache.set("item.key", frontPageNews);

Optionally you can specify an expiration (in seconds) for the cache:

// Cache for 15 minutes
cache.set("item.key", frontPageNews, 60 * 15);

You can retrieve the data later:

News news = cache.get("item.key");

You can also supply a Callable that generates stores the value if no value is found in the cache:

News maybeCached = cache.getOrElse("item.key", () -> lookUpFrontPageNews());

To remove an item from the cache use the remove method:

cache.remove("item.key");

§Accessing different caches

It is possible to access different caches. The default cache is called play, and can be configured by creating a file called ehcache.xml. Additional caches may be configured with different configurations, or even implementations.

If you want to access multiple different ehcache caches, then you’ll need to tell Play to bind them in application.conf, like so:

play.cache.bindCaches = ["db-cache", "user-cache", "session-cache"]

By default, Play will try to create these caches for you. If you would like to define them yourself in ehcache.xml, you can set:

play.cache.createBoundCaches = false

Now to access these different caches, when you inject them, use the NamedCache qualifier on your dependency, for example:

import play.cache.*;
import play.mvc.*;

import javax.inject.Inject;

public class Application extends Controller {

    @Inject @NamedCache("session-cache") CacheApi cache;

    // ...
}

§Caching HTTP responses

You can easily create a smart cached action using standard Action composition.

Note: Play HTTP Result instances are safe to cache and reuse later.

Play provides a default built-in helper for the standard case:

@Cached(key = "homePage")
public Result index() {
    return ok("Hello world");
}

§Custom implementations

It is possible to provide a custom implementation of the CacheApi that either replaces, or sits along side the default implementation.

To replace the default implementation, you’ll need to disable the default implementation by setting the following in application.conf:

play.modules.disabled += "play.api.cache.EhCacheModule"

Then simply implement CacheApi and bind it in the DI container.

To provide an implementation of the cache API in addition to the default implementation, you can either create a custom qualifier, or reuse the NamedCache qualifier to bind the implementation.

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