Rdf4j 3.0 contains several backward incompatible changes. We distinguish changes that affect users of the Rdf4j tools (Console, Workbench, Server), changes that affect users of the Rdf4j APIs and libraries, and changes that affect third party Sail / Repository implementations. See the linked issues for further details.
rdf4j tools users
Due to an up upgrade to Spring 5.1, Rdf4j Server and Rdf4j Workbench now require a servlet container that supports Servlet API 3.1. For Apache Tomcat, that means Tomcat 8 or better. For Eclipse Jetty, it means Jetty 9 or better.