How to open Javadoc JAR file in web browser
- Rename the file spigot-language-kotlin-1.0.3-javadoc.jar to spigot-language-kotlin-1.0.3-javadoc.zip
- Use your favourite unzip tool (WinRAR / WinZIP) to extract it, now you have a folder spigot-language-kotlin-1.0.3-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 "spigot-language-kotlin-1.0.3-sources.jar" -d "spigot-language-kotlin-1.0.3-javadoc" -subpackages 
