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Spring MVC RxJava handlers

A Spring Boot starter for RxJava integration

Build Status Coverage Status


Add the Spring Boot starter to your project:


Note: If you need RxJava 1.4.x support use version 1.0.0. For RxJava2 use 2.x.



Registers Spring's MVC return value handlers for rx.Observable and rx.Single types. You don't need to any longer use blocking operations or assign the values to DeferredResult or ListenableFuture instead you can declare that your REST endpoint returns Observable.


public static class InvoiceResource {

    @RequestMapping(method = RequestMethod.GET, value = "/invoices", produces = MediaType.APPLICATION_JSON_UTF8_VALUE)
    public Observable<Invoice> getInvoices() {

        return Observable.just(
                new Invoice("Acme", new Date()),
                new Invoice("Oceanic", new Date())

The Observable will wrap any produced results into a list and make it process through Spring's message converters. In case if you need to return exactly one result you can use rx.Single instead. You can think of rx.Single as counterpart of Spring's DeferredResult or ListenableFuture. Also with rx.Single, and unlike with rx.Observable it is possible to return ResponseEntity in order to have the control of the HTTP headers or the status code of the response.

Note: The HandlerReturnValueHandler for Observable uses 'toList' operator to aggregate the results, which is not workable with really long infinitive running Observables, from which is not possible to unsubscribe.

In some scenarios when you want to have more control over the async processing you can use either ObservableDeferredResult or SingleDeferredResult, those are the specialized implementation of DeferredResult allowing for instance of setting the processing timeout per response.

Server side events

Spring 4.2 introduced ResponseBodyEmitter for long-lived HTTP connections and streaming the response data. One of available specialized implementations is ObservableSseEmitter that allows to send server side event produced from rx.Observable.


public static class Events {

    @RequestMapping(method = RequestMethod.GET, value = "/messages")
    public ObservableSseEmitter<String> messages() {
        return new ObservableSseEmitter<String>(
                "message 1", "message 2", "message 3"

This will output:

data: message 1

data: message 2

data: message 3

The SSE can be conveniently consumed by a JavaScript client for instance.


The only supported property is rxjava.mvc.enabled which allows to disable this extension.

rxjava.mvc.enabled=true # true by default


Apache 2.0