I am using Wildfly server for my application. I am running this server through intellij plugin. Whenever I run this application I am getting an error message
"Error running 'JBoss 9.0.1.Final': Unable to connect to the localhost:8080"
Here is my configuration in intellij.

Edit your standalone.xml, add this to it and try again.
Also, check your Java version. Wildfly 9 uses Java 7/8, maybe you need to downgrade Java version or update Wildfly to 14 or 15.
You can check here the best versions of each, so you can start your server without problems. Regards.