Attaching additional javadoc in Intellij IDEA

If using maven:

"right click on your pom.xml" -> "Maven" -> then choose "Download Sources and Documentation"

To avoid this in the future: "Preferences" -> "Build, Execution, Deployment" -> "Build Tools" -> "Maven" -> "Importing" -> Check the Automatically download Sources and Documentation boxes.

Credit to Yacov Schondorf and Stephen Boesch from Intellij user forums.

You can attach javadoc to any library you have configure in your module or project. Just access the project structure windows (File -> Project Structure), then select "modules" and select the module that has the dependency you want to configure.

Then select the "Dependencies" tab, select the dependency that's missing the javadoc and click "Edit". In the window that just showed up you see two buttons "Add" and "Specify Javadoc URL". If you have the javadoc in a jar file select the first one, if you want to point to a web site that contains the javadoc select the latest. That's it.