Is a WAR file all that you have or do you have additional artifacts deployed? The class cast exception is usually due to two different class loaders loading the two classes in question. But since javax.xml.parsers.DocumentBuilderFactory is in the
Java runtime, I suspect that there might be multiple JARs with that class.
Edit the run.conf (or run.conf.bat) file to add "-verbose:class" to the JAVA_OPTS and restart the app server. This option causes the JVM to print the location of the JAR file for each class loaded. This generates a lot of output to be sure to redirect stdout and stderr to a file. Then look through the file to see where javax.xml.parsers.DocumentBuilderFactory and oracle.xml.jaxp.JXDocumentBuilderFactory are being loaded from. That should give you some clue as to what went wrong.