How to open Javadoc JAR file in web browser
- Rename the file quarkus-spring-data-jpa-api-2.1.SP2-javadoc.jar to quarkus-spring-data-jpa-api-2.1.SP2-javadoc.zip
- Use your favourite unzip tool (WinRAR / WinZIP) to extract it, now you have a folder quarkus-spring-data-jpa-api-2.1.SP2-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 "quarkus-spring-data-jpa-api-2.1.SP2-sources.jar" -d "quarkus-spring-data-jpa-api-2.1.SP2-javadoc" -subpackages 
