Import the Gradle project via build.gradle inside your preferred IDE.
IntelliJ: https://www.jetbrains.com/help/idea/2017.1/importing-a-gradle-project-or-a-gradle-module.html
Eclipse: http://www.vogella.com/tutorials/EclipseGradle/article.html

The de.uniba.dsg.SpotifyApi class is the main entry point for using the Spotify Api wrapper functionality provided by se.michaelthelin.spotify:spotify-web-api-java. To be able to authenticate your requests, set your Spotify API credentials in src/main/resources/config.properties.

All service interfaces are located inside de.uniba.dsg.interfaces. Main entry point for the JAX-RS web service is the de.uniba.dsg.jaxrs.MusicApi class. For JAX-WS take a look at the de.uniba.dsg.jaxws.MusicApi interface and the de.uniba.dsg.jaxws.MusicApiImpl class. Resource implementations are located inside de.uniba.dsg.jaxws.resources and de.uniba.dsg.jaxrs.resources. The shared model and entity classes for both web services are located inside de.uniba.dsg.models.

Start the JAXRS server via de.uniba.dsg.jaxrs.JaxRsServer.java.
Start the JAXWS server via de.uniba.dsg.jaxws.JaxWsServer.java.