If you want to set up JRE, you can do it as shown here. To add java libraries see Runtime Configuration.

If you want to set the JRE, you can do it by selecting Window  Preferences.

After clicking the option, you will see the following window:

Expand the Java item and select the Installed JREs item as shown above. If you have already installed JRE 1.8, you will see the following window:

Here, you manage the available Java Runtime Environments. The JRE being used for graph run is set up in CloverDX  Runtime. See Runtime Configuration