Grails Redis ETag Plugin

This plugin is intended to work in pair with the Grails cache-headers plugin, in particular it's providing a solution to generate, store and retrieve ETag values in Redis, avoiding DB hits. Redis is thus used as a central cache for ETags, and the plugin can be used by multiple instances of the same application that will share the same "ETag repository".

Installation

Dependency :

compile ':redis-etag:1.1'

In order to access the Redis server where ETags are stored, the plugin uses the configuration of the Grails redis plugin.

Typically, you'd have something like this in your grails-app/conf/Config.groovy file:

grails.redisEtag.connectiontouse = 'eTag' // not mandatory. If not declared 'eTag' is the default value
grails {  // example of configuration
    redis {
        poolConfig {
            // jedis pool specific tweaks here, see jedis docs & src
            // ex: testWhileIdle = true
        }
        database = 1          // each other grails env can have a private one
        port = 6379
        host = 'localhost'
        timeout = 2000 // default in milliseconds
        password = '' // defaults to no password
        connections {
            eTag {
                //enabled = false // ETag enabled by default
                database = 2
                host = 'localhost'  // will override the base one
                defaultTTL = 60 * 60 * 24 // seconds (default is one day)
                eTagStringPrefix = 'eTag:' // prefix used in Redis keys (default is 'eTag:')
            }
        }
    }
}

There are two additional entries in the configuration respect a standard Redis plugin configuration:

• defaultTTL: indicates the amount of seconds to use as TTL for ETag keys in Redis
• eTagStringPrefix: indicates the prefix that will be used for ETag keys in Redis

There is also a specific configuration key that allows selecting which Redis connection to use:

• grails.redisEtag.connectiontouse: the Redis connection that the plugin must use. Can be any of those specified in the redis plugin configuration. If not found, 'eTag' is the default one (and, if there is no 'eTag' connection, the base connection will be used.)

Plugin Usage

Operations and typical usage

As explained below, the plugin can be used in several ways (injected methods/service), but the set of operations and parameters available are always the same. The plugin provides operations:

• getRedisETag(String objectType, String objectIdentifier): retrieves the ETag value associated with the given object ID and type.
• evictRedisETag(String objectType, String objectIdentifier): retrieves the ETag value associated with the given object ID and type.

The objectType parameter allows separating the entities by a 'type', while the objectIdentifier allows distinguishing individual objects of the same type.

Typically, a Domain Class name (e.g, 'Book') will be used as type, and a Domain Class instance ID will be used as identifier. Thus, the getRedisETag() operation will be called inside the etag (provided by the Grails cache-headers plugin) block of a controller action so the ETag associated with a given Domain Class instance is retrieved from Redis without hitting the DB, and the evictRedisETag() operation will be called from the code (typically a service) that updates or deletes the instances of that Domain Class.

Controllers/Services dynamic methods

At application startup/reload each Grails controller and service gets injected the two operations described above with the same names (getRedisETag() and evictRedisETag()).

Here is an example of usage along with the Grails cache-headers plugin:

def index(Long id)

    withCacheHeaders {
        etag {
            getRedisETag(name: 'Book', id: id as String)
        }
        generate {
            Book book = Book.get(id)
            render(view:'bookDisplay', model:[book:book])
        }
    }
}

RedisETagService Bean

def redisETagService

The redisETagService has 2 methods corresponding to the 2 operations described above.

This service is a standard Spring bean that can be injected and used in controllers, services, etc.

Examples:

String myBookETag = redisETagService.getRedisETag('Book', 3)

redisETagService.evictRedisETag('book', 3)

Release Notes

• 1.0 - released 23/02/2015 - this is the first released revision of the plugin.
• 1.1 - released 16/03/2015 - now wildcard (*) is accepted inside eviction id String.
• 1.2 - released 03/08/2015 - now based on Grails redis plugin 1.6.6 version instead of 1.5.0.

Credits

This plugin is sponsored by GameTube.