One other way to generate Java API doc that I followed is to use IntelliJ (an Eclipse-like IDE) and follow the procedure here:
https://www.jetbrains.com/idea/help/generating-javadoc-reference-for-a-project.html
You can download IntelliJ (Community Edition) from:
https://www.jetbrains.com/idea/download/
Note:
1. The ODL code has to be git cloned into your pc and used as the project in IntelliJ
2. You might see errors in the console when generating the doc but you can ignore them
3. The same procedure might be possible using Eclipse but I vaguely remember hitting an issue.
