Build the fatjar with the command below. This shades cats which is necessary for the meanwhile as spark 3 has a dependency on a milestone version of cats-kernel 2.0.0 which is binary incompatible with the released versions of cats 2.x.x
sbt assembly
Then you should be able to run with:
YOUR_SPARK_INSTALL/bin/spark-submit \
--class "example.UriDemo" \
--master "local[4]" \
target/scala-2.12/SparkExample-assembly-0.1.0-SNAPSHOT.jar
And you should see www.example.com printed to the console