2.1. Prerequisites
2.1.1. Installing a Java Development Kit (JDK)
Before installing JBoss Web Server, you must first install a supported Java Development Kit (JDK).

Subscribe your Red Hat Enterprise Linux system to the appropriate supplementary channel:

Red Hat Enterprise Linux Server Supplementary for Red Hat Enterprise Linux 6

Red Hat Enterprise Linux Server Supplementary for Red Hat Enterprise Linux 7

The installation guide only suggests subscribing to the Supplementary repositories. The supplementary repositories only contain the IBM JDK. The standard RHEL repository contains OpenJDK and then there is a separate Oracle-Third-Party repository for Oracle's JDK.

Here are the subscription manager repos:

IBM:
rhel-6-server-supplementary-rpms
rhel-7-server-supplementary-rpms

Oracle:
rhel-6-server-thirdparty-oracle-java-rpms
rhel-7-server-thirdparty-oracle-java-rpms

OpenJDK:
rhel-6-server-rpms
rhel-7-server-rpms