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Clojure bindings for RxJava.


Binaries and dependency information for Maven, Ivy, Gradle and others can be found at

Example for Leiningen:

[io.reactivex/rxclojure "x.y.z"]

and for Gradle:

compile 'io.reactivex:rxclojure:x.y.z'

and for Maven:


and for Ivy:

<dependency org="io.reactivex" name="rxclojure" rev="x.y.z" />

Clojure Bindings

This library provides convenient, idiomatic Clojure bindings for RxJava.

The bindings try to present an API that will be comfortable and familiar to a Clojure programmer that's familiar with the sequence operations in clojure.core. It "fixes" several issues with using RxJava with raw Java interop, for example:

  • Argument lists are in the "right" order. So in RxJava, the function applied in is the second argument, while here it's the first argument with one or more Observables as trailing arguments
  • Operators take normal Clojure functions as arguments, bypassing need for the interop described below
  • Predicates accomodate Clojure's notion of truth
  • Operators are generally names as they would be in clojure.core rather than the Rx names

There is no object wrapping going on. That is, all functions return normal rx.Observable objects, so you can always drop back to Java interop for anything that's missing in this wrapper.

Basic Usage

Most functionality resides in the rx.lang.clojure.core namespace and for the most part looks like normal Clojure sequence manipulation:

(require '[rx.lang.clojure.core :as rx])

(->> my-observable
     (rx/map (comp clojure.string/lower-case :first-name))
     (rx/map clojure.string/lower-case)
     (rx/filter #{"bob"})
     (rx/into []))
;=> An Observable that emits a single vector of names

Blocking operators, which are useful for testing, but should otherwise be avoided, reside in rx.lang.clojure.blocking. For example:

(require '[rx.lang.clojure.blocking :as rxb])

(rxb/doseq [{:keys [first-name]} users-observable]
  (println "Hey," first-name))
;=> nil

Open Issues

  • The missing stuff mentioned below
  • group-by val-fn variant isn't implemented in RxJava
  • There are some functions for defining customer Observables and Operators (subscriber, operator*, observable*). I don't think these are really enough for serious operator implementation, but I'm hesitant to guess at an abstraction at this point. These will probably change dramatically.

What's Missing

This library is an ongoing work in progress driven primarily by the needs of one team at Netflix. As such some things are currently missing:

  • Highly-specific operators that we felt cluttered the API and were easily composed from existing operators, especially since we're in not-Java land. For example, Observable.sumLong().
  • Most everything involving schedulers
  • Most everything involving time
  • Observable.window and Observable.buffer. Who knows which parts of these beasts to wrap?

Of course, contributions that cover these cases are welcome.

Low-level Interop

This adaptor provides functions and macros to ease Clojure/RxJava interop. In particular, there are functions and macros for turning Clojure functions and code into RxJava Func* and Action* interfaces without the tedium of manually reifying the interfaces.

Basic Usage

Requiring the interop namespace

The first thing to do is to require the namespace:

(ns my.namespace
  (:require [rx.lang.clojure.interop :as rx])
  (:import [rx Observable]))

or, at the REPL:

(require '[rx.lang.clojure.interop :as rx])

Using rx/fn

Once the namespace is required, you can use the rx/fn macro anywhere RxJava wants a rx.functions.Func object. The syntax is exactly the same as clojure.core/fn:

(-> my-observable
    (.map (rx/fn [v] (* 2 v))))

If you already have a plain old Clojure function you'd like to use, you can pass it to the rx/fn* function to get a new object that implements rx.functions.Func:

(-> my-numbers
    (.reduce (rx/fn* +)))

Using rx/action

The rx/action macro is identical to rx/fn except that the object returned implements rx.functions.Action interfaces. It's used in subscribe and other side-effect-y contexts:

(-> my-observable
    (.map (rx/fn* transform-data))
    (.finallyDo (rx/action [] (println "Finished transform")))
    (.subscribe (rx/action [v] (println "Got value" v))
                (rx/action [e] (println "Get error" e))
                (rx/action [] (println "Sequence complete"))))

Using Observable/create

As of 0.17, rx.Observable/create takes an implementation of rx.Observable$OnSubscribe which is basically an alias for rx.functions.Action1 that takes an rx.Subscriber as its argument. Thus, you can just use rx/action when creating new observables:

; A simple observable that emits 0..9 taking unsubscribe into account
(Observable/create (rx/action [^rx.Subscriber s]
                     (loop [i 0]
                       (when (and (< i 10) (.isUnsubscribed s))
                         (.onNext s i)
                         (recur (inc i))))
                     (.onCompleted s)))


Here are a few things to keep in mind when using this interop:

  • Keep in mind the (mostly empty) distinction between Func and Action and which is used in which contexts
  • If there are multiple Java methods overloaded by Func arity, you'll need to use a type hint to let the compiler know which one to choose.
  • Methods that take a predicate (like filter) expect the predicate to return a boolean value. A function that returns a non-boolean value will result in a ClassCastException.