Getting org.jboss.resteasy.spi.UnhandledException or java.lang.ClassCastException when forwarding REST request

Issue

When forwarding a RESTEASY request , for example :

@Path("/")
public class MockResource {

    private ServletContext ctx;

    @GET
    @Path("/create")
    @Produces(MediaType.TEXT_HTML)
    public void createMock(@Context HttpServletRequest req, @Context HttpServletResponse res) throws IOException, ServletException {
        ctx.getRequestDispatcher(getPath("create")).forward(req, res);
    }
    …
}

The following exceptions are thrown:

• org.jboss.resteasy.spi.UnhandledException: javax.servlet.ServletException: Original SevletRequest or wrapped original ServletRequest not passed to RequestDispatcher in violation of SRV.8.2 and SRV.14.2.5.1

Or

• java.lang.ClassCastException: $Proxy280 cannot be cast to javax.servlet.ServletRequestWrapper at org.apache.catalina.core.ApplicationFilterFactory.createFilterChain(ApplicationFilterFactory