Based on https://github.com/jameswalton/kafka-streams with explicit creation of objects

core.clj

(ns kafka-streams-test.core
  (:import [org.apache.kafka.streams.kstream KStreamBuilder ValueMapper]
            [org.apache.kafka.streams KafkaStreams StreamsConfig]
           [org.apache.kafka.common.serialization Serdes])
  (:gen-class))

(def props
  {StreamsConfig/APPLICATION_ID_CONFIG "dictionary-words-count"
   StreamsConfig/BOOTSTRAP_SERVERS_CONFIG "localhost:9092"
   StreamsConfig/KEY_SERDE_CLASS_CONFIG (.getName (.getClass (Serdes/String)))
   StreamsConfig/VALUE_SERDE_CLASS_CONFIG (.getName (.getClass (Serdes/String)))})

(def input-topic
  (into-array String ["my-input-topic"]))

(defn dofunc-and-print [f v]
  (println (str "The value is " v))
  (f v))

(def transform-fn
  (fn [v]
    (str "The sent message is: " v)))

(defn -main [& args]
  (let [config (StreamsConfig. props)
        builder (KStreamBuilder.)
        source (->
                (.stream builder input-topic)
                (.mapValues (reify ValueMapper (apply [_ v] (dofunc-and-print transform-fn v))))
                (.to "my-output-topic")
                )
        streams (KafkaStreams. builder config)
        ]
    (prn "starting")
    (.start streams)
    (Thread/sleep 6000)
    (.close streams)
    (prn "stopping")))