How to open Javadoc JAR file in web browser
- Rename the file vertx-promises-groovy-1.1.0-ALPHA2-javadoc.jar to vertx-promises-groovy-1.1.0-ALPHA2-javadoc.zip
- Use your favourite unzip tool (WinRAR / WinZIP) to extract it, now you have a folder vertx-promises-groovy-1.1.0-ALPHA2-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 "vertx-promises-groovy-1.1.0-ALPHA2-sources.jar" -d "vertx-promises-groovy-1.1.0-ALPHA2-javadoc" -subpackages 
