WildFly, as well as JBoss AS 7, has a class loading system considerably different from the previous versions. The WildFly class loading is based on JBoss Modules. Instead of using the hierarchy of class loading that is most commonly known, WildFly class loading is based on modules that have to explicitly define their dependencies on other modules. The WildFly deployments are also in modules and do not have access to classes that are defined in JAR files on the application server unless a dependency is defined for these classes.