Fraction Authoring


The composable pieces of WildFly Swarm are called fractions. Each fraction starts with a single Maven-addressable artifact which may transitively bring in others.

The pom.xml

It is useful to set at least a pair of properties, specifying the version of the WildFly Swarm SPI and fraction-plugin being used:


You can include all of the primary bits of WildFly Swarm using the bom-all artifact in a <dependencyManagement> import. Additionally, you’ll need two more dependencies added in order to write CDI components to configure the server.



Additionally, the wildfly-swarm-fraction-plugin should be configured within the parent pom.xml so that it fires for every sub-module:


What’s in a Fraction

A "fraction" can include all or none of the following components. Ultimately a fraction contributes configuration or capabilities to a runtime system.

Package Layout

For a given fraction, a unique package root is required. In the usual case of the core code, it matches the pattern of org.wildfly.swarm.CAPABILITY, such as org.wildfly.swarm.undertow or org.wildfly.swarm.naming.

Within the root the following additional sub-packages may be found:

  • deployment

  • detect

  • internal

  • runtime

The org.wildfly.swarm.CAPABILITY.detect package holds classes that are used for determining if the fraction applies to a given deployment.

The org.wildfly.swarm.CAPABILITY.runtime and org.wildfly.swarm.CAPABILITY.internal package holds classes that are considered "back-end" components, loaded via our internal CDI implementation in order to configure and setup the server.

The org.wildfly.swarm.CAPABILITY.deployment package holds other classes that should not be considered either part of the front-end API of the fraction exposed to users, nor a part of the back-end components to configure the server. Instead, the .deployment package is a sidecar to hold additional classes that may be added to deployment archives.

The module.conf

Alongside your pom.xm you need at least an empty module.conf file to signal the plugin that your build is actually a fraction.

This file is used to enumerate the JBoss-Modules dependencies your fraction may have, and helps produce the resulting module.xml files for your fraction.

In this file, one per line, you may list the module dependencies you may have. If your fraction relies on runtime linking to other fractions, they should typically be listed in this file.


Maven Artifact Dependencies

You cannot specify maven artifact style dependencies in the module.conf file. If you have such dependencies, you need to create a JBoss-Modules module.xml descriptor in your fraction’s src/main/resources/modules directory. For example, the org.wildfly.swarm:fluentd fraction includes the following src/main/resources/modules/org/fluentd/main/module.xml to declare dependencies on:

  • org.fluentd:fluent-logger:${fluentd.version}

  • org.msgpack:msgpack:0.6.8

  • com.googlecode.json-simple:json-simple:1.1.1

  • org.javassist:javassist:3.18.1-GA

  • org.slf4j:slf4j-api:1.7.7.jbossorg-1

  • org.jboss.logmanager:jboss-logmanager-ext:${version.jboss-logmanager-ext}

<?xml version="1.0" ?>
<module xmlns="urn:jboss:module:1.3" name="org.fluentd">

    <artifact name="org.fluentd:fluent-logger:${fluentd.version}"/>
    <artifact name="org.msgpack:msgpack:0.6.8"/>
    <artifact name="com.googlecode.json-simple:json-simple:1.1.1"/>
    <artifact name="org.javassist:javassist:3.18.1-GA"/>
    <artifact name="org.slf4j:slf4j-api:1.7.7.jbossorg-1"/>
    <artifact name="org.jboss.logmanager:jboss-logmanager-ext:${version.jboss-logmanager-ext}"/>

    <module name="org.jboss.logmanager"/>
    <module name="javax.json.api"/>
    <module name=""/>

For more information on the syntax of the JBoss-Modules module.xml descriptor, see

Generated modules

The wildfly-swarm-fraction-plugin generates a number of module.xml descriptors depending on what features it has found in the faction. You may override any one of these descriptors by providing the corresponding module.xml in your src/main/resources/modules directory.

  • api: this is a module definition that depends on all modules specified in module.conf + swarm container and cdi modules, the fraction artifact, excluding the <fraction-root-package>/{runtime,deployment} packages if they exist. It is used to configure fractions, container, etc, when running in Uber jar mode when JBoss-Modules is fully active

  • deployment: is a module definition that depends on all modules specified in module.conf, the fraction:main module, excluding the <fraction-root-package>/{runtime,META-INF} paths, the fraction artifact excluding the <fraction-root-package>/{runtime,internal,META-INF} packages. This module is automatically added as a module dependency to any deployments. It’s a convenient way to had code into the user deployment for handling integrations with the container.

  • main: This is a module definition similar to API, but active when running from IDE or wildfly-swarm:run

  • runtime: this is a module definition that depends on the fraction artifact with the root excluded, the main module, swarm and cdi modules, and all modules in module.conf. This module is used to load the fraction and any of its runtime code. These modules are what JBoss Modules loads for use by the WF self contained server to make extensions, subsystems, etc available for the deployment.

The *

If the fraction includes configuration capabilities, or otherwise alters the runtime system through deployments or adjustments to the server, it may include an implementation of org.wildfly.swarm.spi.api.Fraction.

Any opaque POJO configuration details that are required may be added in the implementation, and will be made available to the back-end runtime portion during server boot-up to control configuration.

In the event that no particular configuration values are required, no Fraction implementation is required. If provided, it should reside in the absolute root of the fraction java package, such as org.wildfly.swarm.undertow.UndertowFraction.

package com.mycorp.cheese;

import java.util.Set;
import java.util.HashSet;
import org.wildfly.swarm.spi.api.Fraction;

public class CheeseFraction implements Fraction {
  // arbitrary configuration parameters are allowed

  public void cheese(String type) {
    this.cheeses.add( type );

  public void cheeses(Set<String> types) {
    this.cheeses.addAll( types );

  public Set<String> cheeses() {
    return this.cheeses;

  private Set<String> cheeses = new HashSet<>();

Runtime CDI Components

Within the runtime sub-package of the fraction, a variety of CDI-enabled components may be used. Within these classes, you can use typical CDI mechanisms such as @Inject, @Produces, and Instance<> in order to accomplish whatever is required for your fraction. Typically these components would, at the minimum, inject their own fraction. They should each be marked as @Singleton.

public class MyComponents implements Whatever {

  private MyFraction myFraction;



If your fraction needs an opportunity to alter or otherwise prepare all deployed archives, you may implement the org.wildfly.swarm.spi.api.DeploymentProcessor interface.

public class MyArchivePreparer implements DeploymentProcessor {

    private final Archive archive;

    private MyFraction myFraction;

    public MyArchivePreparer(Archive archive) {
        this.archive = archive;

    public void process() throws Exception {
        WARArchive war =;
Useful Annotations

There are a few additional annotations that you may include on your fraction class:

  • @WildFlyExtension(module = "org.keycloak.keycloak-adapter-subsystem"), if the fraction is installed, then the named WildFly Extension will also be installed. This is equivalent to the <extension> element in the WildFly standalone.xml.

  • @WildFlySubsystem("keycloak"), if the fraction is installed, then the named WildFly Subsystem will also be included. This is equivalent to the <subsystem> element in the WildFly standalone.xml.

  • @DeploymentModule(name = "org.keycloak.keycloak-core") adds the indicated module dependency to the deployment archives that are appropriate to a fraction.

Injecting IndexView

If your fraction needs an opportunity to process the Jandex metadata of all deployed archives, you can inject org.jboss.jandex.IndexView into your DeploymentProcessor instance, e.g.

public class ServiceClientProcessor implements DeploymentProcessor {
    private final Archive<?> archive;
    private final IndexView index;

    public ServiceClientProcessor(Archive archive, IndexView index) {
        this.archive = archive;
        this.index = index;


Most of the heavy-lifting of configuration may occur within implementations of org.wildfly.swarm.spi.api.Customizer.

If your fraction is always present with other fractions, cross-fraction manipulation may be achieved.

Two different executions of Customizers occur. All customizers annotated with @Pre are fired, followed by all annotated with @Post.

public class MyCustomizer implements Customizer {

  private MyFraction myFraction;

  private UndertowFraction undertowFraction;

  public void customize() {
    if ( undertowHasSSL() ) {

Archive producers

In some cases, a fraction implicitly produces a deployment archive by its simple presence in the dependency graph. For example, including org.wildfly.swarm:jolokia ensures that the Jolokia web-app is deployed. This is accomplished by having a CDI component that @Produces a ShrinkWrap Archive. No particular interface is required to be implemented.

public MyArchiveProducers {

  private MyFraction myFraction;

  Archive myManagementConsole() {
    WARArchive archive = ...  // produces the Archive any way you like
    archive.setContextRoot( myFraction.getContextRoot() );
    return archive;

The @ConfigurationValue annotation

Any of your components can also @Inject configuration values that are sourced from either project-defaults.yml based upon the currently active stage, or system properties if no project stage is available.

@Inject @ConfigurationValue('my.db.url')
private String dbUrl;

@Inject @ConfigurationValue('my.age')
private int age;

Transitive dependencies

If your fraction depends upon the presence of a Servlet container being configured, you should add a dependency on the necessary fractions into your pom.xml


By doing this, a user must only include your fraction, and the Undertow fraction will be dragged along implicitly into their application.