In the preceding example, we did the following: we annotated our classes with JAX-RS annotations, built the code using Swarm Maven plugin, and obtained a runnable Swarm-based JAR. The resulting JAR is much smaller than a full application server. The reason for that is that Swarm has wrapped our code in only those parts of WildFly that it needs to work. Now, we will look in greater detail at this statement.

Let's run the application created in the preceding chapter again:

mvn wildfly-swarm:run

Let's look at the beginning of the console output:

Take a look at the lines of the log in the red rectangle. Swarm is informing us that it has installed four fractions: JAX-RS, Undertow, Elytron, and Logging. However, what does it mean by that and what actually is a fraction?

The fraction is a part of the functionality needed by an application. To be more precise, fraction...