Clojure XML Parsing

问题:

I can not find any info on how to parse xml documents and access elements.

I have found two ways to parse the xml document

(clojure.zip/xml-zip (clojure.xml/parse file))

and

(parse-seq file)

but i can seem to find any info on how to process the resulting structure?

Source file's refers to zip-query.clj on how to query the result but that seems to missing too.

回答1:

Suppose you have the following xml to parse in your file:

<high-node>
   <low-node>my text</low-node>
</high-node>

you load clojure.xml:

user=> (use 'clojure.xml)

when parsed, the xml will have the following structure:

{:tag :high-node, :attrs nil, :content [{:tag :low-node, :attrs nil, :content ["my text"]}]}

and then you can seq over the content of the file to get the content of the low-node:

user=> (for [x (xml-seq 
              (parse (java.io.File. file)))
                 :when (= :low-node (:tag x))]
         (first (:content x)))

("my text")

Similarly, if you wanted to have access to the entire list of information on low-node, you would change the :when predicate to (= (:high-node (:tag x))):

user=> (for [x (xml-seq 
              (parse (java.io.File. file)))
                 :when (= :high-node (:tag x))]
         (first (:content x)))

({:tag :low-node, :attrs nil, :content ["my text"]})

This works because the keywords can operate as functions. See Questions about lists and other stuff in Clojure and Data Structures: Keywords

回答2:

The above answer works, but I find it a lot easier to use clojure.data.zip.xml (used to be clojure-contrib.zip-filter.xml prior to Clojure 1.3).

file:

myfile.xml:

<songs>
  <track id="t1"><name>Track one</name></track>
  <track id="t2"><name>Track two</name></track>
</songs>

code:

; Clojure 1.3
(ns example
  (:use [clojure.data.zip.xml :only (attr text xml->)]) ; dep: see below
  (:require [clojure.xml :as xml]
            [clojure.zip :as zip]))

(def xml (xml/parse "myfile.xml"))
(def zipped (zip/xml-zip xml))
(xml-> zipped :track :name text)       ; ("Track one" "Track two")
(xml-> zipped :track (attr :id))       ; ("t1" "t2")

Unfortunately, you need to pull in a dependency on data.zip to get this nice read/filter functionality. It's worth the dependency :) In lein it would be (as of 17-Aug-2013):

[org.clojure/data.zip "0.1.1"]

And as for docs for data.zip.xml ... I just look at the relatively small source file here to see what is possible. Another good SO answer here, too.