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