在Clojure 1.3中，如何读写一个文件 [英] In Clojure 1.3, How to read and write a file

问题描述

我想知道在clojure 1.3中阅读和编写文件的推荐方式。

1. 如何阅读


2. 如何读取文件


3. 如何编写新文件





解决方案

假设我们只在这里执行文本文件而不是一些疯狂的二进制文件。





数字1：如何读取整个文件到内存中。 b $ b

 （slurp/tmp/test.txt）
  

当它是一个非常大的文件时，不推荐使用。





第2行：如何逐行读取文件 / p>



 （使用'clojure.java.io）
（with-open [rdr（reader/ tmp / test。 txt）] 
（doseq [line（line-seq rdr）] 
（println line）））
  

$ b b


with-open 宏关心读者在body的结尾处关闭。阅读器函数强制字符串（它也可以做一个URL等）到 BufferedReader 。 line-seq 提供一个延迟序列。要求将延迟seq结果的下一个元素转换为从阅读器读取的行。





第3个：如何写入新文件

 （使用'clojure.java.io）
（with-open [wrtr test.txt）] 
（.write wrtr要写入的行））
  

再次， with-open 注意 BufferedWriter 在正文结尾处关闭。 Writer将一个字符串强制转换为一个 BufferedWriter ，你使用通过java interop：（。write wrtrsomething）。





您也可以使用 spit ，与 slurp ：

 （spit/tmp/test.txt要写入的行）
  
 
 
 
 第4项：在现有文件中附加一行。 
 （使用'clojure.java.io）
（with-open [wrtr（writer/tmp/test.txt：append true）] 
（.write wrtr要附加的行））
  
 with append option。
 
 
 
或再次使用 spit ，与 slurp ：
 （spit/tmp/test.txt要写入的行：append true）
  
  PS：要更明确地说明您正在阅读和写作到文件而不是其他文件，您可以先创建一个File对象，然后将其强制为 BufferedReader 或作者：
 （reader（file/tmp/test.txt））
 ;;或
（作者（文件tmp / test.txt））
  
文件功能
  PS2：有时，它可以方便地查看当前目录）是。您可以通过两种方式获取绝对路径：
 （System / getPropertyuser.dir）
  
 
 
 
或
  >（java.io.File。。）.getAbsolutePath）
  
 
I'd like to know the "recommended" way of reading and writing a file in clojure 1.3 .

How to read the whole file
How to read a file line by line
How to write a new file
How to add a line to an existing file

解决方案
Assuming we're only doing text files here and not some crazy binary stuff.

Number 1: how to read an entire file into memory.
(slurp "/tmp/test.txt")
Not recommended when it is a really big file.

Number 2: how to read a file line by line.
(use 'clojure.java.io)
(with-open [rdr (reader "/tmp/test.txt")]
  (doseq [line (line-seq rdr)]
    (println line)))
The with-open macro takes care that the reader is closed at the end of the body. The reader function coerces a string (it can also do a URL, etc) into a BufferedReader. line-seq delivers a lazy seq. Demanding the next element of the lazy seq results into a line being read from the reader.

Number 3: how to write to a new file.
(use 'clojure.java.io)
(with-open [wrtr (writer "/tmp/test.txt")]
  (.write wrtr "Line to be written"))
Again, with-open takes care that the BufferedWriter is closed at the end of the body. Writer coerces a string into a BufferedWriter, that you use use via java interop: (.write wrtr "something").

You could also use spit, the opposite of slurp:
(spit "/tmp/test.txt" "Line to be written")
Number 4: append a line to an existing file.
(use 'clojure.java.io)
(with-open [wrtr (writer "/tmp/test.txt" :append true)]
  (.write wrtr "Line to be appended"))
Same as above, but now with append option.

Or again with spit, the opposite of slurp:
(spit "/tmp/test.txt" "Line to be written" :append true)
PS: To be more explicit about the fact that you are reading and writing to a File and not something else, you could first create a File object and then coerce it into a BufferedReader or Writer:
(reader (file "/tmp/test.txt"))
;; or
(writer (file "tmp/test.txt"))
The file function is also in clojure.java.io.

PS2: Sometimes it's handy to be able to see what the current directory (so ".") is. You can get the absolute path in two ways:
(System/getProperty "user.dir") 
or 
(-> (java.io.File. ".") .getAbsolutePath)


                        
这篇关于在Clojure 1.3中，如何读写一个文件的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！