Micronaut Mastery: Using Reactor Mono And Flux

Micronaut is reactive by nature and uses RxJava2 as implementation for the Reactive Streams API by default. RxJava2 is on the compile classpath by default, but we can easily use Project Reactor as implementation of the Reactive Streams API. This allows us to use the Reactor types Mono and Flux. These types are also used by Spring’s Webflux framework and makes a transition from Webflux to Micronaut very easy.

How we do use Project Reactor in our Micronaut application? We only have to add the dependency the Project Reactory core library to our project. In the following example we add it to our build.gradle file as:

Now we can use Mono and Flux as return types for methods. If we use them in our controller methods Micronaut will make sure the code is handled on the Netty event loop. This means we must handle blocking calls (like accessing a database using JDBC) with care and make sure a blocking call invoked from the controller methods is handled on a different thread.

In the following example we have a simple controller. Some of the methods use a repository implementation with code that access a databases using JDBC. The methods of the repository implementation are not reactive, therefore we must use Mono.fromCallable with Reactor’s elastic scheduler to make sure the code is called on separate threads and will not block our Netty event loop.

The repository interface looks like this:

Let’s write a Spock specification to test if our controller works correctly:

Written with Micronaut 1.0.0.M4.

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About mrhaki

My name is Hubert A. Klein Ikkink also known as mrhaki. I work at the great IT company JDriven. Here I work on projects with Groovy & Grails, Gradle and Spring. At JDriven we focus on SpringSource technologies. All colleagues want to learn new technologies, support craftmanship and are very eager to learn. This is truly a great environment to work in. You can contact me via Google+ or @mrhaki.

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