How to open Javadoc JAR file in web browser
- Rename the file eclipse-2020-09-22.12.14.release-javadoc.jar to eclipse-2020-09-22.12.14.release-javadoc.zip
- Use your favourite unzip tool (WinRAR / WinZIP) to extract it, now you have a folder eclipse-2020-09-22.12.14.release-javadoc
- Double click index.html will open the index page on your default web browser.
How to generate Javadoc from a source JAR?
Running the command javadoc:
javadoc --ignore-source-errors -encoding UTF-8 -sourcepath "eclipse-2020-09-22.12.14.release-sources.jar" -d "eclipse-2020-09-22.12.14.release-javadoc" -subpackages 
