How to open Javadoc JAR file in web browser
- Rename the file wildfly-preview-feature-pack-content-28.0.1.Final-javadoc.jar to wildfly-preview-feature-pack-content-28.0.1.Final-javadoc.zip
- Use your favourite unzip tool (WinRAR / WinZIP) to extract it, now you have a folder wildfly-preview-feature-pack-content-28.0.1.Final-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 "wildfly-preview-feature-pack-content-28.0.1.Final-sources.jar" -d "wildfly-preview-feature-pack-content-28.0.1.Final-javadoc" -subpackages 
