Custom log4j appender in Clojure

core.clj

(ns woof.core
  (:gen-class)
  (:require [clojure.tools.logging :as log])
  (:import StringAppender))

(defn -main
  "I don't do a whole lot ... yet."
  [& args]
  (log/info "Hello, world!")
  (println "Done")
  (println (StringAppender/getLogs)))

log4j.properties

log4j.rootLogger=INFO, console
log4j.logger.example=DEBUG
log4j.appender.console=StringAppender
log4j.appender.console.layout=org.apache.log4j.PatternLayout
log4j.appender.console.layout.ConversionPattern=%-5p %c: %m%n

project.clj

(defproject woof "0.1.0-SNAPSHOT"
  :description "FIXME: write description"
  :url "http://example.com/FIXME"
  :license {:name "Eclipse Public License"
            :url "http://www.eclipse.org/legal/epl-v10.html"}
  :dependencies [[org.clojure/clojure "1.8.0"]
                 [org.slf4j/slf4j-log4j12 "1.7.25"]
                 [org.clojure/tools.logging "0.4.0"]]
  :main ^:skip-aot woof.core
  :aot [woof.woof]
  :target-path "target/%s"
  :profiles {:uberjar {:aot :all}})

woof.clj

(ns woof.woof
  (:import (org.apache.log4j.spi LoggingEvent))
  (:gen-class
   :extends org.apache.log4j.AppenderSkeleton
   :name StringAppender
   :methods [^:static [getLogs [] String]]))

(def logs (atom ""))

(defn -append [this ^LoggingEvent logging-event]
  (swap! logs str (.getMessage logging-event) "\n"))

(defn -close [this])

(defn -requiresLayout [this] false)

(defn -getLogs []
  @logs)