How to open Javadoc JAR file in web browser
- Rename the file de.undercouch.download.gradle.plugin-5.4.0-javadoc.jar to de.undercouch.download.gradle.plugin-5.4.0-javadoc.zip
- Use your favourite unzip tool (WinRAR / WinZIP) to extract it, now you have a folder de.undercouch.download.gradle.plugin-5.4.0-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 "de.undercouch.download.gradle.plugin-5.4.0-sources.jar" -d "de.undercouch.download.gradle.plugin-5.4.0-javadoc" -subpackages 
