Recently core 1.12 was updated to compile against servlet-api 3.0 jars (although web.xml still declares 2.4). In order to eventually upgrade to Servlet 3.0 features, the app will need to run in a 3.0-compliant container. The embedded Jetty container is currently v6, but the minimum Jetty version that supports 3.0 is v8
Jetty has been upgraded to the 8.x line to comply with Java 8 in
TRUNK-4660, but it would be nice to investigate upgrading Jetty to 9.x here.
Jetty is setup at https://github.com/openmrs/openmrs-core/blob/master/webapp/pom.xml#L106
You can run it following: https://wiki.openmrs.org/display/docs/Maven
Please change the version of Jetty in pom.xml and test if OpenMRS starts and runs correctly using mvn jetty:run.