/usr/share/java/jetty9-websocket-server-9.2.21.v20170120.jar is in libjetty9-extra-java 9.2.21-1+deb9u1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/java/jetty9-websocket-server.jar
/usr/share/java/jetty9-websocket-server.jar