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Akka 2.4 RC1 发布，Actor 开发模型库

Akka 2.4 RC1 发布，相比最后一个 M 版本，主要改进如下：

Persistence Query types for LevelDB
protobuf serialization for Cluster Sharding, Cluster Client and Cluster Singleton
possibility to use Distributed Data module as storage for the state of the sharding coordinator instead of using Akka Persistence, contribution by Evgeniy Ostapenko
improvements of the ReceivePipeline , contribution by jeremystone

Akka 2.4.0 主要改进如下：

we dropped support for Java 6 & 7 as announced in the last roadmap update , and now require Java 8 or later
we dropped support for Scala 2.10, kept 2.11 and added 2.12 (which is at milestone 2 currently); this is in keeping with our policy to support the Scala version that is “current” when the first milestone comes out plus any later version that is published during this series’ lifetime
Akka Persistence was promoted to a fully supported module (not experimental)
added experimental stream based API for the Query Side of Akka Persistence (implementations must be provided by query plugins corresponding to the journal plugins for the various data stores)
improved support for Akka Persistence event migrations by Serializer with String Manifest and Event Adapters and prepared comprehensive documentation of strategies for schema evolution of persistent events
made Akka Persistence failure handling more robust and support rejections of events
Akka Persistence can now use multiple different Journals within one ActorSystem (thanks to Andrei Pozolotin , who also split out ClusterMetrics into their own module)
introduced Persistent FSM , thanks to an awesome contribution from leonidb
simplified setting up Akka Clusters behind NAT (including inside Docker containers)
we added the experimental Akka Typed module previously codenamed Project Gålbma, a new way of formulating Actor interactions with full type-system support
we promoted the ClusterSingleton , ClusterClient , DistributedPubSub and ClusterSharding patterns to fully a supported Cluster Tools module, including various API and configuration improvements
ClusterSharding also learnt a few new tricks ( graceful shutdown , asynchronous shard allocation, reviving entries after migration thanks to Dominic Black , and more flexible use of roles [thanks to Richard Marscher )
use custom failure detection in ClusterClient to avoid quarantining in case of transient network failures
added experimental Akka Distributed Data which was previously known as Akka Data Replication (see akka-data-replication migration guide ), the Distributed Data module is useful for sharing eventually consistent data (CRDTs) between nodes in an Akka Cluster
the SLF4J logging adapter can now apply the log filtering rules prior to sending to the EventStream, see the migration guide but the biggest feature is probably that Akka 2.4 will be binary backwards compatible with Akka 2.3, see the detailed description below.