Fastest Solution
Use the adoptopenjdk cask
See also https://discourse.brew.sh/t/how-to-install-openjdk-with-brew/712/4
To install latest:
brew install --cask adoptopenjdk
To install a specific version
brew tap AdoptOpenJDK/openjdk
brew install --cask adoptopenjdk8
brew install --cask adoptopenjdk9
Manual Solution
If you are looking to just bring down the binary without actually installing it, simply navigate to https://adoptopenjdk.net