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Redis Cache module for Play framework

Note: This version supports Play framework 2.4.x with JDK 8.
For previous versions see older releases.

By default, Play framework 2 is delivered with EHCache module implementing CacheApi. Unfortunately, this module suffers from a very inconvenient issue: as the ClassLoaders are evolved on application recompilation during a development, the class versions does not match thus the cache is wiped on every compilation. That might result in repeated logging in, loosing a session or computing an extensive value. All these things very slow down development.

The goal of this module is to enable the redis-server key/value cache storage to be smoothly used within the Play framework 2. Furthermore, besides the backward compatibility with the CacheApi, it introduces more evolved API called play.api.cache.redis.CacheApi. As the cache implementation uses Akka actor system, it is completely non-blocking and asynchronous. Furthermore, besides the basic methods such as get, set and remove it provides more convenient methods such as expire, exists and invalidate.

This library delivers a single module with following implementations of the API:

  1. play.api.cache.redis.CacheApi
  2. play.api.cache.redis.CacheAsyncApi
  3. play.api.cache.CacheApi
  4. play.cache.CacheApi

First, the CacheApi is extended play.api.cache.CacheApi and it implements the connection in the blocking manner. Second, the CacheAsyncApi enables non-blocking connection providing results through scala.concurrent.Future. Third, the synchronous implementation also implements standard CacheApi bundled within Play framework.

How to add the module into the project

This module builds over Brando connector and is intended only for Scala version of the Play framework.

To your SBT build.sbt add the following lines:

// redis-server cache
libraryDependencies += "com.github.karelcemus" %% "play-redis" % "1.0.0"

// repository with the Brando connector 
resolvers += "Brando Repository" at "http://chrisdinn.github.io/releases/"

Now we must enable our redis cache module and disable default Play's EhCache module. Into application.conf and following two lines:

# disable default Play framework cache plugin
play.modules.disabled += "play.api.cache.EhCacheModule"

# enable redis cache module
play.modules.enabled += "play.api.cache.redis.RedisCacheModule"

How to use this module

When you have the library added to your project, you can safely inject the play.api.cache.redis.CacheApi trait for the synchronous cache. If you want the asynchronous implementation, then inject play.api.cache.redis.CacheAsyncApi. There might be some limitations with data types but it should not be anything major. (Note: it uses Akka serialization. Supported data types are primitives, objects serializable through the java serialization and collections.) If you encounter any issue, please feel free to report it.

Example:

import scala.concurrent.Future
import scala.concurrent.duration._

import play.api.cache.redis.CacheApi

class MyController @Inject() ( cache: CacheApi ) {

  cache.set( "key", "value" )
  // returns Option[ T ] where T stands for String in this example
  cache.get[ String ]( "key" )
  cache.remove( "key" )

  cache.set( "object", MyCaseClass() )
  // returns Option[ T ] where T stands for MyCaseClass
  cache.get[ MyCaseClass ]( "object" )

  // returns Future[ Try[ String ] ] where the value string
  // should be Success( "OK" ) or Failure( ex )
  cache.set( "key", 1.23 )

  // returns Option[ Double ]
  cache.get[ Double ]( "key" )
  // returns Option[ MyCaseClass ]
  cache.get[ MyCaseClass ]( "object" )

  // returns T where T is Double. If the value is not in the cache
  // the computed result is saved
  cache.getOrElse( "key" )( 1.24 )

  // same as getOrElse but works for Futures. It returns Future[ T ]
  cache.getOrFuture( "key" )( Future( 1.24 ) )

  // returns Unit and removes a key/keys from the storage
  cache.remove( "key" )
  cache.remove( "key1", "key2" )
  cache.remove( "key1", "key2", "key3" )
  // remove all expects a sequence of keys, it performs same be behavior
  // as remove methods, they are just syntax sugar
  cache.removeAll( "key1", "key2", "key3" )

  // invalidates all keys in the redis server! Beware using it
  cache.invalidate()

  // refreshes expiration of the key if present
  cache.expire( "key", 1.second )

  // returns true if the key is in the storage, false otherwise
  cache.exists( "key" )
  
  // returns all keys matching given pattern. Beware, complexity is O(n).
  // It executes KEYS command
  cache.matching( "page/1/*" )
  
  // removes all keys matching given pattern. Beware, complexity is O(n).
  // It executes KEYS and DEL commands in a transaction
  cache.removeMatching( "page/1/*" )

  // when we import `play.api.cache.redis._` it enables us
  // using both `java.util.Date` and `org.joda.time.DateTime` as expiration
  // dates instead of duration. These implicits are useful when
  // we know the data regularly changes, e.g., at midnight, at 3 AM, etc.
  // We do not have compute the duration ourselves, the library
  // can do it for us
  import play.api.cache.redis._
  cache.set( "key", "value", DateTime.parse( "2015-12-01T00:00" ).asExpiration )
}
Please keep in mind that this implementation is blocking!

Configuration

There is already default configuration but it can be overwritten in your conf/application.conf file.

Key Type Default Description
play.cache.redis.host String localhost redis-server address
play.cache.redis.port Int 6379 redis-server port
play.cache.redis.database Int 1 redis-server database, 1-15
play.cache.redis.timeout Duration 1s connection timeout
play.cache.redis.dispatcher String akka.actor.default-dispatcher Akka actor
play.cache.redis.configuration String static Defines which configuration source enable. Accepted values are static, env, custom
play.cache.redis.password String null When authentication is required, this is the password. Value is optional.
play.cache.redis.connection-string-variable String REDIS_URL Name of the environment variable with the connection string. This is used in combination with the env configuration. This allows customization of the variable name in PaaS environment. Value is optional.

Connection settings on different platforms

In various environments there are various sources of the connection string defining how to connect to Redis instance. For example, at localhost we are interested in direct definition of host and port in the application.conf file. However, this approach does not fit all environments. For example, Heroku supplies REDIS_URL environment variable defining the connection string. To resolve this diversity, the library expects an implementation of the Configuration trait available through DI. By default, it enables static configuration source, i.e., it reads the settings from the static configuration file. Another supplied configuration reader is env, which reads the environment variable such as REDIS_URL but the name is configurable. To disable built-in providers you are free to set custom and supply your own implementation of the Configuration trait.

Running on Heroku

To enable redis cache on Heroku we have to do the following steps:

  1. add library into application dependencies
  2. enable RedisCacheModule
  3. disable EhCacheModule
  4. set play.cache.redis.configuration: env
  5. done, we can run it and use any of 3 provided interfaces

Custom configuration source

However, there are scenarios when we need to customize the configuration to better fit our needs. Usually, we might encounter this when we have a specific development flow or use a specific PaaS. To enable redis cache implementation with customized configuration we have to do the following steps:

  1. add library into application dependencies
  2. enable RedisCacheModule
  3. disable EhCacheModule
  4. set play.cache.redis.configuration: custom
  5. Implement play.api.cache.redis.Configuration trait
  6. Register the implementation into DI provider. This is specific for each provider. If you are using Guice, which is Play's default DI provider, then look here. It gives you a hint how to register the implementation during application start.
  7. done, we can run it and use any of 3 provided interfaces

Worth knowing to avoid surprises

The library does not enable the redis module by default. It is to avoid conflict with Play's default EhCache. The Play discourages disabling modules within the library thus it leaves it up to developers to disable EhCache and enable Redis manually. This also allows you to use EhCache in your dev environment and redis in production. Nevertheless, this module replaces the EHCache and it is not intended to use both implementations along.