Getting Started

This section contains information that should help you get going with Reactor Netty. It includes the following information:

1. Introducing Reactor Netty

Suited for Microservices Architecture, Reactor Netty offers backpressure-ready network engines for HTTP (including Websockets), TCP, and UDP.

2. Prerequisites

Reactor Netty runs on Java 8 and above.

It has transitive dependencies on:

  • Reactive Streams v1.0.4

  • Reactor Core v3.x

  • Netty v4.1.x

3. Understanding the BOM and versioning scheme

Reactor Netty is part of the Project Reactor BOM (since the Aluminium release train). This curated list groups artifacts that are meant to work well together, providing the relevant versions despite potentially divergent versioning schemes in these artifacts.

The versioning scheme has changed between 0.9.x and 1.0.x (Dysprosium and Europium).

Artifacts follow a versioning scheme of MAJOR.MINOR.PATCH-QUALIFIER while the BOM is versioned using a CalVer inspired scheme of YYYY.MINOR.PATCH-QUALIFIER, where:

  • MAJOR is the current generation of Reactor, where each new generation can bring fundamental changes to the structure of the project (which might imply a more significant migration effort)

  • YYYY is the year of the first GA release in a given release cycle (like 1.0.0 for 1.0.x)

  • .MINOR is a 0-based number incrementing with each new release cycle

    • in the case of projects, it generally reflects wider changes and can indicate a moderate migration effort

    • in the case of the BOM it allows discerning between release cycles in case two get first released the same year

  • .PATCH is a 0-based number incrementing with each service release

  • -QUALIFIER is a textual qualifier, which is omitted in the case of GA releases (see below)

The first release cycle to follow that convention is thus 2020.0.x, codename Europium. The scheme uses the following qualifiers (note the use of dash separator), in order:

  • -M1..-M9: milestones (we don’t expect more than 9 per service release)

  • -RC1..-RC9: release candidates (we don’t expect more than 9 per service release)

  • -SNAPSHOT: snapshots

  • no qualifier for GA releases

Snapshots appear higher in the order above because, conceptually, they’re always "the freshest pre-release" of any given PATCH. Even though the first deployed artifact of a PATCH cycle will always be a -SNAPSHOT, a similarly named but more up-to-date snapshot would also get released after eg. a milestone or between release candidates.

Each release cycle is also given a codename, in continuity with the previous codename-based scheme, which can be used to reference it more informally (like in discussions, blog posts, etc…​). The codenames represent what would traditionally be the MAJOR.MINOR number. They (mostly) come from the Periodic Table of Elements, in increasing alphabetical order.

Up until Dysprosium, the BOM was versioned using a release train scheme with a codename followed by a qualifier, and the qualifiers were slightly different. For example: Aluminium-RELEASE (first GA release, would now be something like YYYY.0.0), Bismuth-M1, Californium-SR1 (service release would now be something like YYYY.0.1), Dysprosium-RC1, Dysprosium-BUILD-SNAPSHOT (after each patch, we’d go back to the same snapshot version. would now be something like YYYY.0.X-SNAPSHOT so we get 1 snapshot per PATCH)

4. Getting Reactor Netty

As mentioned earlier, the easiest way to use Reactor Netty in your core is to use the BOM and add the relevant dependencies to your project. Note that, when adding such a dependency, you must omit the version so that the version gets picked up from the BOM.

However, if you want to force the use of a specific artifact’s version, you can specify it when adding your dependency as you usually would. You can also forego the BOM entirely and specify dependencies by their artifact versions.

4.1. Maven Installation

The BOM concept is natively supported by Maven. First, you need to import the BOM by adding the following snippet to your pom.xml. If the top section (dependencyManagement) already exists in your pom, add only the contents.

<dependencyManagement> (1)
    <dependencies>
        <dependency>
            <groupId>io.projectreactor</groupId>
            <artifactId>reactor-bom</artifactId>
            <version>2024.0.0-M3</version> (2)
            <type>pom</type>
            <scope>import</scope>
        </dependency>
    </dependencies>
</dependencyManagement>
1 Notice the dependencyManagement tag. This is in addition to the regular dependencies section.
2 As of this writing, 2024.0.0-M3 is the latest version of the BOM. Check for updates at github.com/reactor/reactor/releases.

Next, add your dependencies to the relevant reactor projects, as usual (except without a <version>). The following listing shows how to do so:

<dependencies>
    <dependency>
        <groupId>io.projectreactor.netty</groupId>
        <artifactId>reactor-netty-core</artifactId> (1)
        (2)
    </dependency>
</dependencies>
<dependencies>
    <dependency>
        <groupId>io.projectreactor.netty</groupId>
        <artifactId>reactor-netty-http</artifactId>
    </dependency>
</dependencies>
1 Dependency on Reactor Netty
2 No version tag here

4.2. Gradle Installation

The BOM concept is supported in Gradle since version 5. The following listing shows how to import the BOM and add a dependency to Reactor Netty:

dependencies {
    // import a BOM
    implementation platform('io.projectreactor:reactor-bom:2024.0.0-M3') (1)

    // define dependencies without versions
    implementation 'io.projectreactor.netty:reactor-netty-core' (2)
    implementation 'io.projectreactor.netty:reactor-netty-http'
}
1 As of this writing, 2024.0.0-M3 is the latest version of the BOM. Check for updates at github.com/reactor/reactor/releases.
2 There is no third : separated section for the version. It is taken from the BOM.

4.3. Milestones and Snapshots

Milestones and developer previews are distributed through the Spring Milestones repository rather than Maven Central. To add it to your build configuration file, use the following snippet:

Milestones in Maven
<repositories>
	<repository>
		<id>spring-milestones</id>
		<name>Spring Milestones Repository</name>
		<url>https://repo.spring.io/milestone</url>
	</repository>
</repositories>

For Gradle, use the following snippet:

Milestones in Gradle
repositories {
  maven { url 'https://repo.spring.io/milestone' }
  mavenCentral()
}

Similarly, snapshots are also available in a separate dedicated repository (for both Maven and Gradle):

-SNAPSHOTs in Maven
<repositories>
	<repository>
		<id>spring-snapshots</id>
		<name>Spring Snapshot Repository</name>
		<url>https://repo.spring.io/snapshot</url>
	</repository>
</repositories>
-SNAPSHOTs in Gradle
repositories {
  maven { url 'https://repo.spring.io/snapshot' }
  mavenCentral()
}

5. Support and policies

The entries below are mirroring github.com/reactor/.github/blob/main/SUPPORT.adoc

5.1. Do you have a question?

Search Stack Overflow first; discuss if necessary

If you’re unsure why something isn’t working or wondering if there is a better way of doing it please check on Stack Overflow first and if necessary start a discussion. Use relevant tags among the ones we monitor for that purpose:

If you prefer real-time discussion, we also have a few Gitter channels:

  • reactor is the historic most active one, where most of the community can help

  • reactor-core is intended for more advanced pinpointed discussions around the inner workings of the library

  • reactor-netty is intended for netty-specific questions

Refer to each project’s README for potential other sources of information.

We generally discourage opening GitHub issues for questions, in favor of the two channels above.

5.2. Our policy on deprecations

When dealing with deprecations, given a version A.B.C, we’ll ensure that:

  • deprecations introduced in version A.B.0 will be removed no sooner than version A.B+1.0

  • deprecations introduced in version A.B.1+ will be removed no sooner than version A.B+2.0

  • we’ll strive to mention the following in the deprecation javadoc:

    • target minimum version for removal

    • pointers to replacements for the deprecated method

    • version in which method was deprecated

This policy is officially in effect as of January 2021, for all modules in 2020.0 BOMs and newer release trains, as well as Dysprosium releases after Dysprosium-SR15.
Deprecation removal targets are not a hard commitment, and the deprecated methods could live on further than these minimum target GA versions (ie. only the most problematic deprecated methods will be removed aggressively).
That said, deprecated code that has outlived its minimum removal target version may be removed in any subsequent release (including patch releases, aka service releases) without further notice. So users should still strive to update their code as early as possible.