Java的System.out.println(...)是对PrintStream示例的println方法的调用。您需要用自己的示例替换System.out流并捕获其内容：

(import [java.io ByteArrayOutputStream PrintStream])

(def out-buffer (java.io.ByteArrayOutputStream.))

(System/setOut (java.io.PrintStream. out-buffer true "UTF-8"))

(defn out-str []
  (.toString out-buffer "UTF-8"))

但是在REPL中要小心，因为它使用System.out来打印结果，所以当你全局替换它时，它会破坏你的REPL示例。
您甚至可以编写一个宏来捕获System.out的内容，然后恢复原始的PrintStream示例：

(defmacro with-system-out-str [& body]
  `(let [out-buffer# (ByteArrayOutputStream.)
         original-out# System/out
         tmp-out# (PrintStream. out-buffer# true "UTF-8")]
     (try
       (System/setOut tmp-out#)
       ~@body
       (finally
         (System/setOut original-out#)))
     (.toString out-buffer# "UTF-8")))

(with-system-out-str
  (.println System/out "Hi"))
;; => "Hi\n"

您可以将输出保存到文件中，然后读取文件的内容。

(def foo-file (clojure.java.io/writer "foo.txt"))

(binding [*out* foo-file]
  (println "Foo, bar."))

(println "Slurp: " (slurp "foo.txt"))

Tupelo库包括with-system-out-str和with-system-err-str