It is not enough to run the jar, as Maven does not "incorporate" the dependencies of a module into the jar it is building. Either run the jar with
java -jar yourJar.jar -cp pathToTheSpymemcached.jar
where you replace yourJar.jar
and pathToTheSpymemcached.jar
appropriately or you may have a look at this: How can I create an executable JAR with dependencies using Maven?