The java buildpack is hacked together from the CNBP samples repo and tutorials.
First you'll need to install pack and jam.
export REPO="[your repo name here]" # e.g. gcr.io/your-project
cd stack/wolfi
jam create-stack --config stack.toml --build-output build.oci --run-output run.oci
skopeo copy oci-archive:run.oci docker://${REPO}/wolfi-stack-base-run
skopeo copy oci-archive:build.oci docker://${REPO}/wolfi-stack-base-build
cd ../../builder
pack builder create ${REPO}/wolfi-base-builder --config ./builder.toml
cd ../sample/recaptcha-demo
pack build recaptcha-demo --builder ${REPO}/wolfi-base-builder
docker run --rm -p 8080:8080 recaptcha-demo