protected String[] getAnnotationValue(Annotation a) {
        RequiresPermissions rpAnnotation = (RequiresPermissions) a;
        return rpAnnotation.value();
    }
Returns the annotation {@link RequiresPermissions#value value}, from which the Permission will be constructed.

@param a the RequiresPermissions annotation being inspected.
@return the annotation's <code>value</code>, from which the Permission will be constructed.
core/src/main/java/org/apache/shiro/authz/aop/PermissionAnnotationHandler.java