You might've forgot to add a dependency or it's written wrong. Also, you might be using incompatible versions of Java and Hibernate. More on this here: https://goo.gl/SjSlRA
If you're using Hibernate, this indicates you're missing FasterXML Classmate dependency, which you can add to your dependencies. To add it, the groupId is com.fasterxml and artifactId is Classmate.
org.hibernate.MappingException: Unable to load class declared as <mapping class="org.appfuse.model.User"/> in the configuration: at java.net.URLClassLoader$1.run(URLClassLoader.java:200)