How to install JDK sources?

How can I download the source code of Java on my local machine, so I can reference it in an IDE?

Example for Java 8:

sudo apt-get install openjdk-8-source

apt-get puts it under the relevant JDK location as src.zip: /usr/lib/jvm/java-8-openjdk-amd64/src.zip

Intellij IDEA recognized it automatically and started showing me the source code.

In case of java 11 (on Ubuntu 18.04) I did:

First I install jdk 11:

sudo apt install openjdk-11-jdk

I install the sources like this:

sudo apt-get install openjdk-11-source

And I found them in /usr/lib/jvm/openjdk-11/lib/src.zip

I use Eclipse so I go inside Eclipse's menu Window -> Preferences -> Installed JREs and inside select java-11-openjdk-amd64 -> edit -> select the jar (jrt-fs.jar) -> Source Attachment -> External location -> /usr/lib/jvm/openjdk-11/lib/src.zip

Now I happily read the java documentation! :)

Best of luck to all!