JBoss AS7.x wont run on JDK8! Only supported java versions are 6 and 7.
If you want to use JDK8 you should to upgrade to WildFly 8+
When you try to run AS7 of JDK8 it will hang during the boot, root problem is https://issues.jboss.org/browse/WFLY-2057 which was fixed in early WildFly 8 development cycle.
There are plenty of threads on this topic and what you can do to manually fix it if you need to, see AS 7 on Java 8 for more.
Keep in mind that fix for WFLY-2057 only makes it run JDK8, you still cannot use all Java 8 features in all aspects of the server. Different aspects of this ware fixed in WildFly 8.1, 8.2 and some in WildFly 9.
On related topic JBoss EAP 6 which is based on AS7 got full JDK8 support starting version 6.3.3.GA and 6.4.0.GA