blocks|key|250766|text|如果文件可以放入内存中，则可以使用slurp和spit对其进行读写：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|250767|(def+s+(slurp+"filename.txt"))|code-block|syntax|javascript|250768|(%25s现在包含字符串形式的文件内容)|250769|(spit+"newfile.txt"+s)|250770|如果没有退出，这将创建newfile.txt并写入文件内容。如果想要追加到该文件，可以执行以下操作|250771|(spit+"filename.txt"+s+:append+true)|250772|要逐行读写文件，您需要使用Java的读取器和写入器。它们被包装在名称空间clojure.java.io中：|250773|(ns+file.test
++(:require+[clojure.java.io+:as+io]))

(let+[wrtr+(io/writer+"test.txt")]
++(.write+wrtr+"hello,+world!\n")
++(.close+wrtr))

(let+[wrtr+(io/writer+"test.txt"+:append+true)]
++(.write+wrtr+"hello+again!")
++(.close+wrtr))

(let+[rdr+(io/reader+"test.txt")]
++(println+(.readLine+rdr))
++(println+(.readLine+rdr)))
;+"hello,+world!"
;+"hello+again!"|250774|请注意，slurp/spit和读取器/写入器示例之间的区别在于，在后者中，文件保持打开(在let语句中)，并且读取和写入是缓冲的，因此在重复读取/写入文件时效率更高。|250775|以下是更多信息：slurp+spit+clojure.java.io+Java's+BufferedReader+Java's+Writer|offset|length|250776|entityMap|0|LINK|mutability|MUTABLE|url|http://clojuredocs.org/clojure_core/clojure.core/slurp|1|http://clojuredocs.org/clojure_core/clojure.core/spit|2|http://richhickey.github.com/clojure/clojure.java.io-api.html|3|http://download.oracle.com/javase/7/docs/api/java/io/BufferedReader.html|4|http://download.oracle.com/javase/7/docs/api/java/io/Writer.html^0|0|0|0|0|0|0|0|0|0|8|5|0|E|4|1|J|F|2|Z|L|3|1L|D|4|0^^$0|@$1|2|3|4|5|6|7|1E|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|1F|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|1G|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|1H|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|1I|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|1J|8|@]|9|@]|A|$E|F]]|$1|O|3|P|5|6|7|1K|8|@]|9|@]|A|$]]|$1|Q|3|R|5|D|7|1L|8|@]|9|@]|A|$E|F]]|$1|S|3|T|5|6|7|1M|8|@]|9|@]|A|$]]|$1|U|3|V|5|6|7|1N|8|@]|9|@$W|1O|X|1P|1|1Q]|$W|1R|X|1S|1|1T]|$W|1U|X|1V|1|1W]|$W|1X|X|1Y|1|1Z]|$W|20|X|21|1|22]]|A|$]]|$1|Y|3|-4|5|6|7|23|8|@]|9|@]|A|$]]]|Z|$10|$5|11|12|13|A|$14|15]]|16|$5|11|12|13|A|$14|17]]|18|$5|11|12|13|A|$14|19]]|1A|$5|11|12|13|A|$14|1B]]|1C|$5|11|12|13|A|$14|1D]]]]

If the file fits into memory you can read and write it with slurp and spit:

<pre><code>(def s (slurp "filename.txt"))
</code></pre>

(s now contains the content of a file as a string)

<pre><code>(spit "newfile.txt" s)
</code></pre>

This creates newfile.txt if it doesnt exit and writes the file content.
If you want to append to the file you can do 

<pre><code>(spit "filename.txt" s :append true)
</code></pre>

To read or write a file linewise you would use Java's reader and writer. They are wrapped in the namespace clojure.java.io:

<pre><code>(ns file.test
 (:require [clojure.java.io :as io]))

(let [wrtr (io/writer "test.txt")]
 (.write wrtr "hello, world!\n")
 (.close wrtr))

(let [wrtr (io/writer "test.txt" :append true)]
 (.write wrtr "hello again!")
 (.close wrtr))

(let [rdr (io/reader "test.txt")]
 (println (.readLine rdr))
 (println (.readLine rdr)))
; "hello, world!"
; "hello again!"
</code></pre>

Note that the difference between slurp/spit and the reader/writer examples is that the file remains open (in the let statements) in the latter and the reading and writing is buffered, thus more efficient when repeatedly reading from / writing to a file.

Here is more information: <a href="http://clojuredocs.org/clojure_core/clojure.core/slurp" rel="noreferrer">slurp</a> <a href="http://clojuredocs.org/clojure_core/clojure.core/spit" rel="noreferrer">spit</a>
 <a href="http://richhickey.github.com/clojure/clojure.java.io-api.html" rel="noreferrer">clojure.java.io</a>
<a href="http://download.oracle.com/javase/7/docs/api/java/io/BufferedReader.html" rel="noreferrer">Java's BufferedReader</a>
<a href="http://download.oracle.com/javase/7/docs/api/java/io/Writer.html" rel="noreferrer">Java's Writer</a>

blocks|key|3145948|text|假设我们在这里只做文本文件，而不是一些疯狂的二进制东西。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3145949|+1:如何将整个文件读入内存。|offset|length|style|BOLD|3145950|(slurp+"/tmp/test.txt")|code-block|syntax|javascript|3145951|当它是一个非常大的文件时，不推荐。|3145952|第2号:如何逐行读取文件。|3145953|(use+'clojure.java.io)
(with-open+[rdr+(reader+"/tmp/test.txt")]
++(doseq+[line+(line-seq+rdr)]
++++(println+line)))|3145954|with-open宏负责确保读取器在主体的末尾关闭。reader函数将字符串(也可以做网址等)强制转换为BufferedReader。line-seq提供了一个懒惰的seq。请求lazy+seq的下一个元素会导致从读取器读取一行。|CODE|3145955|注意，从Clojure1.7开始，您还可以使用transducers读取文本文件。|3145956|Number+3:如何写入新文件。|3145957|(use+'clojure.java.io)
(with-open+[wrtr+(writer+"/tmp/test.txt")]
++(.write+wrtr+"Line+to+be+written"))|3145958|同样，with-open负责确保BufferedWriter在主体的末尾关闭。编写器将字符串强制转换为可通过java+interop：(.write+wrtr+"something").使用的BufferedWriter。|3145959|您还可以使用与slurp相反的spit|3145960|(spit+"/tmp/test.txt"+"Line+to+be+written")|3145961|编号4:向现有文件追加一行。|3145962|(use+'clojure.java.io)
(with-open+[wrtr+(writer+"/tmp/test.txt"+:append+true)]
++(.write+wrtr+"Line+to+be+appended"))|3145963|和上面一样，但是现在有了append选项。|3145964|或者使用与slurp相反的spit|3145965|(spit+"/tmp/test.txt"+"Line+to+be+written"+:append+true)|3145966|PS:为了更明确地说明您是在读写文件，而不是其他内容，您可以首先创建一个文件对象，然后将其强制到BufferedReader或写入器中：|3145967|(reader+(file+"/tmp/test.txt"))
;;+or
(writer+(file+"tmp/test.txt"))|3145968|file函数也在clojure.java.io中。|3145969|PS2:有时能够看到当前目录的内容是很方便的(所以".")是。您可以通过两种方式获取绝对路径：|3145970|(System/getProperty+"user.dir")+|3145971|或|3145972|(->+(java.io.File.+".")+.getAbsolutePath)|3145973|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/a/47354316/6264^0|0|0|F|0|0|0|0|D|0|0|0|9|1G|E|1V|8|0|N|B|0|0|0|H|0|0|3|9|G|E|1V|Q|2O|E|0|7|5|F|4|0|0|0|E|0|0|0|5|5|D|4|0|0|0|3|1C|E|0|0|0|0|4|0|0|0|0^^$0|@$1|2|3|4|5|6|7|23|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|24|8|@$D|25|E|26|F|G]]|9|@]|A|$]]|$1|H|3|I|5|J|7|27|8|@]|9|@]|A|$K|L]]|$1|M|3|N|5|6|7|28|8|@]|9|@]|A|$]]|$1|O|3|P|5|6|7|29|8|@$D|2A|E|2B|F|G]]|9|@]|A|$]]|$1|Q|3|R|5|J|7|2C|8|@]|9|@]|A|$K|L]]|$1|S|3|T|5|6|7|2D|8|@$D|2E|E|2F|F|U]|$D|2G|E|2H|F|U]|$D|2I|E|2J|F|U]]|9|@]|A|$]]|$1|V|3|W|5|6|7|2K|8|@]|9|@$D|2L|E|2M|1|2N]]|A|$]]|$1|X|3|Y|5|6|7|2O|8|@$D|2P|E|2Q|F|G]]|9|@]|A|$]]|$1|Z|3|10|5|J|7|2R|8|@]|9|@]|A|$K|L]]|$1|11|3|12|5|6|7|2S|8|@$D|2T|E|2U|F|U]|$D|2V|E|2W|F|U]|$D|2X|E|2Y|F|U]|$D|2Z|E|30|F|U]]|9|@]|A|$]]|$1|13|3|14|5|6|7|31|8|@$D|32|E|33|F|U]|$D|34|E|35|F|U]]|9|@]|A|$]]|$1|15|3|16|5|J|7|36|8|@]|9|@]|A|$K|L]]|$1|17|3|18|5|6|7|37|8|@$D|38|E|39|F|G]]|9|@]|A|$]]|$1|19|3|1A|5|J|7|3A|8|@]|9|@]|A|$K|L]]|$1|1B|3|1C|5|6|7|3B|8|@]|9|@]|A|$]]|$1|1D|3|1E|5|6|7|3C|8|@$D|3D|E|3E|F|U]|$D|3F|E|3G|F|U]]|9|@]|A|$]]|$1|1F|3|1G|5|J|7|3H|8|@]|9|@]|A|$K|L]]|$1|1H|3|1I|5|6|7|3I|8|@$D|3J|E|3K|F|G]|$D|3L|E|3M|F|U]]|9|@]|A|$]]|$1|1J|3|1K|5|J|7|3N|8|@]|9|@]|A|$K|L]]|$1|1L|3|1M|5|6|7|3O|8|@]|9|@]|A|$]]|$1|1N|3|1O|5|6|7|3P|8|@$D|3Q|E|3R|F|G]]|9|@]|A|$]]|$1|1P|3|1Q|5|J|7|3S|8|@]|9|@]|A|$K|L]]|$1|1R|3|1S|5|6|7|3T|8|@]|9|@]|A|$]]|$1|1T|3|1U|5|J|7|3U|8|@]|9|@]|A|$K|L]]|$1|1V|3|-4|5|6|7|3V|8|@]|9|@]|A|$]]]|1W|$1X|$5|1Y|1Z|20|A|$21|22]]]]

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

Number 1: how to read an entire file into memory.

<pre><code>(slurp "/tmp/test.txt")
</code></pre>

Not recommended when it is a really big file.

Number 2: how to read a file line by line.

<pre><code>(use 'clojure.java.io)
(with-open [rdr (reader "/tmp/test.txt")]
 (doseq [line (line-seq rdr)]
 (println line)))
</code></pre>

The <code>with-open</code> 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 <code>BufferedReader</code>. <code>line-seq</code> delivers a lazy seq. Demanding the next element of the lazy seq results into a line being read from the reader.

Note that from Clojure 1.7 onwards, you can also use <a href="https://stackoverflow.com/a/47354316/6264">transducers</a> for reading text files.

Number 3: how to write to a new file.

<pre><code>(use 'clojure.java.io)
(with-open [wrtr (writer "/tmp/test.txt")]
 (.write wrtr "Line to be written"))
</code></pre>

Again, <code>with-open</code> takes care that the <code>BufferedWriter</code> is closed at the end of the body. Writer coerces a string into a <code>BufferedWriter</code>, that you use use via java interop: <code>(.write wrtr "something").</code>

You could also use <code>spit</code>, the opposite of <code>slurp</code>:

<pre><code>(spit "/tmp/test.txt" "Line to be written")
</code></pre>

Number 4: append a line to an existing file.

<pre><code>(use 'clojure.java.io)
(with-open [wrtr (writer "/tmp/test.txt" :append true)]
 (.write wrtr "Line to be appended"))
</code></pre>

Same as above, but now with append option.

Or again with <code>spit</code>, the opposite of <code>slurp</code>:

<pre><code>(spit "/tmp/test.txt" "Line to be written" :append true)
</code></pre>

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 <code>BufferedReader</code> or Writer:

<pre><code>(reader (file "/tmp/test.txt"))
;; or
(writer (file "tmp/test.txt"))
</code></pre>

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:

<pre><code>(System/getProperty "user.dir") 
</code></pre>

or 

<pre><code>(-&gt; (java.io.File. ".") .getAbsolutePath)
</code></pre>

blocks|key|2931173|text|对于问题2，有时需要将行流作为第一类对象返回。为了获得一个惰性序列，并且仍然在EOF上自动关闭该文件，我使用了这个函数：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2931174|(use+'clojure.java.io)

(defn+read-lines+[filename]
++(let+[rdr+(reader+filename)]
++++(defn+read-next-line+[]
++++++(if-let+[line+(.readLine+rdr)]
+++++++(cons+line+(lazy-seq+(read-next-line)))
+++++++(.close+rdr)))
++++(lazy-seq+(read-next-line)))
)

(defn+echo-file+[]
++(doseq+[line+(read-lines+"myfile.txt")]
++++(println+line)))|code-block|syntax|javascript|2931175|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Regarding question 2, one sometimes wants the stream of lines returned as a first-class object. To get this as a lazy sequence, and still have the file closed automatically on EOF, I used this function:

<pre><code>(use 'clojure.java.io)

(defn read-lines [filename]
 (let [rdr (reader filename)]
 (defn read-next-line []
 (if-let [line (.readLine rdr)]
 (cons line (lazy-seq (read-next-line)))
 (.close rdr)))
 (lazy-seq (read-next-line)))
)

(defn echo-file []
 (doseq [line (read-lines "myfile.txt")]
 (println line)))
</code></pre>

blocks|key|2931177|text|这就是如何读取整个文件。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2931178|如果文件在资源目录中，您可以这样做：|2931179|(let+[file-content-str+(slurp+(clojure.java.io/resource+"public/myfile.txt")])|code-block|syntax|javascript|2931180|记住需要/使用clojure.java.io。|offset|length|style|CODE|2931181|entityMap^0|0|0|0|7|F|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|R|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|S|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|T|8|@$K|U|L|V|M|N]]|9|@]|A|$]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

This is how to read the whole file.

If the file is in the resource directory, you can do this:

<pre><code>(let [file-content-str (slurp (clojure.java.io/resource "public/myfile.txt")])
</code></pre>

remember to require/use <code>clojure.java.io</code>.

blocks|key|3145988|text|(require+'[clojure.java.io+:as+io])
(io/copy+(io/file+"/etc/passwd")+\*out*\)|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|3145989|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>(require '[clojure.java.io :as io])
(io/copy (io/file "/etc/passwd") \*out*\)
</code></pre>

blocks|key|250783|text|要逐行读取文件，您不再需要求助于互操作：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|250784|(->>+"data.csv"
++++++io/resource
++++++io/reader
++++++line-seq
++++++(drop+1))|code-block|syntax|javascript|250785|这里假设您的数据文件保存在resources目录中，并且第一行是可以丢弃的头信息。|250786|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

To read a file line by line you no longer need to resort to interop:

<pre><code>(-&gt;&gt; "data.csv"
 io/resource
 io/reader
 line-seq
 (drop 1))
</code></pre>

This assumes that your data file is kept in the resources directory and that the first line is header information that can be discarded.

I'd like to know the "recommended" way of reading and writing a file in clojure 1.3 .

<ol>
<li>How to read the whole file</li>
<li>How to read a file line by line</li>
<li>How to write a new file</li>
<li>How to add a line to an existing file</li>
</ol>

In Clojure 1.3, How to read and write a file

Java

我想知道在clojure 1.3中读写文件的“推荐”方法。如何读取整个文件如何逐行读取文件如何写入新文件如何在现有文件中添加一行代码<>G29</code>

问在Clojure 1.3中，如何读写文件
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