The swift client sample uses the openapi-generator-maven-plugin which generates the OpenAPI client code on the fly via a plugin.
The client sample is available on GitHub: https://github.com/lab5e/java-sample and can be built by running
mvn install
Create a new API token in the Span dashboard and run the sample with
java -jar target/target/collection-sample-1.0.0.jar [API token]