with-err-str

with_err_str.clj

(ns lt.jocas.utils.with-err-str
  (:import (java.io PrintStream ByteArrayOutputStream PrintWriter)))

(set! *warn-on-reflection* true)

(defmacro with-err-str
  "Evaluates exprs in a context in which *err* is bound to a fresh
  PrintWriter.  Returns the string created by any nested error printing
  calls."
  [& body]
  `(with-open [baos# (new ByteArrayOutputStream)
               ps# (new PrintStream baos#)
               pw# (new PrintWriter ps# true)]
     (binding [*err* pw#]
       ~@body
       (str baos#))))

(comment
  ;; example
  (with-err-str
    (.println *err* "My error"))
;;=> "My error\n")
 
(comment
 ;; But in another thread doesn't work
 (import '(java.util.concurrent Executor Executors))
 
 (defn print-error-on-thread-pool []
   (let [^Executor executor (Executors/newSingleThreadExecutor)]
     (.execute executor
               ^Runnable (fn []
                           (.println ^PrintWriter *err* "In the thread pool")))
    (.shutdown executor) 
    (.awaitTermination executor 1 TimeUnit/SECONDS)))

  (with-err-str (print-error-on-thread-pool))
;;=> ""
)