In addition, an aggregator structure is provided to build everything as one aggregated build.
mkdir maven cd maven repo init -u https://gitbox.apache.org/repos/asf/maven-sources.git repo sync repo start master --all
Then simply use the cloned content with normal
Once content is cloned with previous instructions, you can build each repository as a separate project.
You can also build absolutely everything in one aggregated run (WARNING: more than 400 modules...):
cd sources mvn --fail-at-end -Prun-its verify mvn --fail-at-end -Preporting site
See Maven Sources Overview description.