Reactive Streams utility API

James Roper james at
Thu Feb 22 00:47:04 UTC 2018

Hi all,

This is an email to give people a heads up that we'd like to look at
creating an API, in the same vein as the JDK8 Streams API, for building
reactive streams (a la JDK9 juc.Flow). Our goals for this are:

* To fill a gap in the JDK where if a developer wants to do even the
simplest of things with a JDK9 juc.Flow, such as map or filter, they need
to bring in a third party library that implements that.
* To produce an API that can build Publishers, Subscribers, Processors, and
complete graphs, for the purposes of consuming APIs that use reactive
streams (for example, JDK9 Http Client).
* To produce an API that aligns closely with, using it for
inspiration for naming, scope, general API shape, and other aspects. The
purpose of this goal is to ensure familiarity of Java developers with the
new API, and to limit the number of concepts Java developers need to
understand to do the different types of streaming offered by the JDK.
* To produce an API that can be implemented by multiple providers
(including an RI in the JDK itself), using the ServiceLoader mechanism to
provide and load a default implementation (while allowing custom
implementations to be manually provided). There are a lot of concerns that
each different streams implementation provides and implements, beyond
streaming, for example monitoring/tracing, concurrency modelling, buffering
strategies, performance aspects of the streams handling including fusing,
and context (eg thread local) propagation. This will allow libraries to use
and provide contracts based on this API without depending on a particular
implementation, and allows developers to select the implementation that
meets their needs.

Non goals:

* To produce a kitchen sink of utilities for working with reactive streams.
There already exist a number of reactive streams implementations that seek
to meet this goal (eg, Akka Streams, Reactor, RxJava), and once you go past
the basics (map, filter, collect), and start dealing with things like fan
in/out, cycles, restarting, etc, the different approaches to solving this
start to vary greatly. The JDK should provide enough to be useful for
typical every day streaming use cases, with developers being able to select
a third party library for anything more advanced.

We will update this list when we have something ready for public review.
This probably won't be far off. Our hope is that we can propose this as a



*James Roper*
*Senior Octonaut*

Lightbend <> – Build reactive apps!
Twitter: @jroper <>

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