Installing Groovy 3 on Debian Bullseye

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The new Debian stable (bullseye) does not come with the latest Apache Groovy version. So, the packaged version still gives warnings with Java 11 and higher. You can download Groovy 3.0.8 as a binary zip file and unzip this in /opt. Easy enough. But you will also want to set it up as "alternative", which is an old Debian mechanism to have alternative versions of the same software installed. It's so old that I had to look up what to type again. So, as an internal note (thx to this QA):

update-alternatives --install \
  /usr/bin/groovy groovy /opt/groovy-3.0.8/bin/groovy 100
update-alternatives --install \
  /usr/bin/groovyConsole groovyConsole /opt/groovy-3.0.8/bin/groovyConsole 100
update-alternatives --install \
  /usr/bin/grape grape /opt/groovy-3.0.8/bin/grape 100
update-alternatives --install \
  /usr/bin/groovyc groovyc /opt/groovy-3.0.8/bin/groovyc 100