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;;; duck_streams.clj -- duck-typed I/O streams for Clojure
;; by Stuart Sierra, http://stuartsierra.com/
;; January 10, 2009
;; Copyright (c) Stuart Sierra, 2008. All rights reserved. The use
;; and distribution terms for this software are covered by the Eclipse
;; Public License 1.0 (http://opensource.org/licenses/eclipse-1.0.php)
;; which can be found in the file epl-v10.html at the root of this
;; distribution. By using this software in any fashion, you are
;; agreeing to be bound by the terms of this license. You must not
;; remove this notice, or any other, from this software.
;; This file defines "duck-typed" I/O utility functions for Clojure.
;; The 'reader' and 'writer' functions will open and return an
;; instance of java.io.BufferedReader and java.io.PrintWriter,
;; respectively, for a variety of argument types -- filenames as
;; strings, URLs, java.io.File's, etc. 'reader' even works on http
;; URLs.
;;
;; Note: this is not really "duck typing" as implemented in languages
;; like Ruby. A better name would have been "do-what-I-mean-streams"
;; or "just-give-me-a-stream", but ducks are funnier.
;; CHANGE LOG
;;
;; January 10, 2009: added *default-encoding*, so streams are always
;; opened as UTF-8.
;;
;; December 19, 2008: rewrote reader and writer as multimethods; added
;; slurp*, file, and read-lines
;;
;; April 8, 2008: first version
(ns clojure.contrib.duck-streams
(:import
(java.io Reader InputStream InputStreamReader
BufferedReader File PrintWriter OutputStream
OutputStreamWriter BufferedWriter Writer
FileInputStream FileOutputStream)
(java.net URI URL MalformedURLException)))
(def *default-encoding* "UTF-8")
(defn #^File file
"Concatenates args as strings returns a java.io.File. Replaces all
/ and \\ with File/separatorChar. Replaces ~ at the start of the
path with the user.home system property."
[& args]
(let [#^String s (apply str args)
s (.replace s \/ File/separatorChar)
s (.replace s \\ File/separatorChar)
s (if (.startsWith s "~")
(str (System/getProperty "user.home")
File/separatorChar (subs s 1))
s)]
(File. s)))
(defmulti #^{:tag BufferedReader
:doc "Attempts to coerce its argument into an open
java.io.BufferedReader. Argument may be an instance of Reader,
BufferedReader, InputStream, File, URI, URL, or String.
If argument is a String, it tries to resolve it first as a URI, then
as a local file name. URIs with a 'file' protocol are converted to
local file names. Uses *default-encoding* as the text encoding.
Should be used inside with-open to ensure the Reader is properly
closed."}
reader class)
(defmethod reader Reader [x]
(BufferedReader. x))
(defmethod reader InputStream [x]
(BufferedReader. (InputStreamReader. x *default-encoding*)))
(defmethod reader File [#^File x]
(reader (FileInputStream. x)))
(defmethod reader URL [#^URL x]
(reader (if (= "file" (.getProtocol x))
(FileInputStream. (.getPath x))
(.openStream x))))
(defmethod reader URI [#^URI x]
(reader (.toURL x)))
(defmethod reader String [#^String x]
(try (let [url (URL. x)]
(reader url))
(catch MalformedURLException e
(reader (file x)))))
(defmethod reader :default [x]
(throw (Exception. (str "Cannot open " (pr-str x) " as a reader."))))
(defmulti #^{:tag PrintWriter
:doc "Attempts to coerce its argument into an open java.io.PrintWriter
wrapped around a java.io.BufferedWriter. Argument may be an
instance of Writer, PrintWriter, BufferedWriter, OutputStream, File,
URI, URL, or String.
If argument is a String, it tries to resolve it first as a URI, then
as a local file name. URIs with a 'file' protocol are converted to
local file names.
Should be used inside with-open to ensure the Writer is properly
closed."}
writer class)
(defmethod writer PrintWriter [x] x)
(defmethod writer BufferedWriter [#^BufferedWriter x]
(PrintWriter. x))
(defmethod writer Writer [x]
;; Writer includes sub-classes such as FileWriter
(PrintWriter. (BufferedWriter. x)))
(defmethod writer OutputStream [x]
(PrintWriter.
(BufferedWriter.
(OutputStreamWriter. x *default-encoding*))))
(defmethod writer File [#^File x]
(writer (FileOutputStream. x)))
(defmethod writer URL [#^URL x]
(if (= "file" (.getProtocol x))
(writer (File. (.getPath x)))
(throw (Exception. (str "Cannot write to non-file URL <" x ">")))))
(defmethod writer URI [#^URI x]
(writer (.toURL x)))
(defmethod writer String [#^String x]
(try (let [url (URL. x)]
(writer url))
(catch MalformedURLException err
(writer (file x)))))
(defmethod writer :default [x]
(throw (Exception. (str "Cannot open <" (pr-str x) "> as a writer."))))
(defn write-lines
"Writes lines (a seq) to f, separated by newlines. f is opened with
writer."
[f lines]
(with-open [#^PrintWriter writer (writer f)]
(loop [lines lines]
(when-let [line (first lines)]
(.write writer (str line))
(.println writer)
(recur (rest lines))))))
(defn read-lines
"Like clojure.core/line-seq but opens f with reader. Automatically
closes the reader AFTER YOU CONSUME THE ENTIRE SEQUENCE."
[f]
(let [read-line (fn this [#^BufferedReader rdr]
(if-let [line (.readLine rdr)]
(lazy-cons line (this rdr))
(.close rdr)))]
(read-line (reader f))))
(defn slurp*
"Like clojure.core/slurp but opens f with reader."
[f]
(with-open [#^BufferedReader r (reader f)]
(let [sb (StringBuilder.)]
(loop [c (.read r)]
(if (neg? c)
(str sb)
(do (.append sb (char c))
(recur (.read r))))))))
(defn spit
"Opposite of slurp. Opens f with writer, writes content, then
closes f."
[f content]
(with-open [#^PrintWriter w (writer f)]
(.print w content)))
(defn pwd
"Returns current working directory as a String. (Like UNIX 'pwd'.)
Note: In Java, you cannot change the current working directory."
[]
(System/getProperty "user.dir"))
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