使用builder創(chuàng)建XML
builder安裝方法：
require 'builder'
x = Builder::XmlMarkup.new(:target =>
$stdout, :indent => 1)
#":target =＞$stdout"參數(shù)：指示輸出內(nèi)
容將被寫(xiě)向標(biāo)準(zhǔn)輸出控制臺(tái)
#":indent =＞1"參數(shù)：XML輸出形式將被縮
進(jìn)一個(gè)空格字符x.instruct! :xml,
:version =>'1.1',:encoding => 'gb2312'
x.comment! "書(shū)本信息"
x.library("shelf" => "Recent Acquisitions") {
x.section("name" => "ruby"){
x.book("isbn" => "0672310001"){
x.title "Programming Ruby"
x.author "Yukihiro "
x.description "Programming Ruby -
The Pragmatic Programmer's Guide"
}
}
}
p x #打印XML
Ruby創(chuàng)建XML輸出結(jié)果：
?xml version="1.1" encoding="gb2312"?>
!-- 書(shū)本信息 -->
library shelf="Recent Acquisitions">
section name="ruby">
book isbn="0672310001">
title>Programming Ruby /title>
author>Yukihiro /author>
description>Programming Ruby - The
Pragmatic Programmer's Guide
/description>
/book>
/section>
/library>
inspect/>
# IO:0x2a06ae8>
使用ReXML解析XML
REXML 是一個(gè)完全用ruby寫(xiě)的processor ,他有多種api，其中兩個(gè)經(jīng)典的api是通過(guò)DOM-like 和SAX-like 來(lái)進(jìn)行區(qū)分的。第一種是將整個(gè)文件讀進(jìn)內(nèi)存，然后存儲(chǔ)為一個(gè)分層的形式(也就是一棵樹(shù)了).而第二種是"parse as you go",當(dāng)你的文件很大，并且內(nèi)存受到限制的時(shí)候，比較適合用這種。
看下面的book.xml:
引用
library shelf="Recent Acquisitions">
section name="Ruby">
book isbn="0672328844">
title>The Ruby Way/title>
author>Hal Fulton/author>
description>
Second edition. The book you are now reading.
Ain't recursion grand?
/description>
/book>
/section>
section name="Space">
book isbn="0684835509">
title>The Case for Mars/title>
author>Robert Zubrin/author>
description>Pushing toward a second home for the human
race.
/description>
/book>
book isbn="074325631X">
title>First Man: The Life of Neil A. Armstrong/title>
author>James R. Hansen/author>
description>Definitive biography of the first man on
the moon.
/description>
/book>
/section>
/library>
1 Tree Parsing(也就是DOM-like)
我們需要require rexml/document 庫(kù)，并且include REXML :
require 'rexml/document'
include REXML
input = File.new("books.xml")
doc = Document.new(input)
root = doc.root
puts root.attributes["shelf"] # Recent Acquisitions
doc.elements.each("library/section") { |e| puts e.attributes["name"] }
# Output:
# Ruby
# Space
doc.elements.each("*/section/book") { |e| puts e.attributes["isbn"] }
# Output:
# 0672328844
# 0321445619
# 0684835509
# 074325631X
sec2 = root.elements[2]
author = sec2.elements[1].elements["author"].text # Robert Zubrin
這里要注意的是xml中的屬性和值被表示為一個(gè)hash，因此我們能夠通過(guò)attributes[]來(lái)提取我們需要的值，元素的值還能通過(guò)類似于path的字符串或者整數(shù)來(lái)取得.其中用整數(shù)取的話，是1-based而不是0-based.
2 Stream Parsing（也就是SAX-like Parsing)
這邊使用了一個(gè)小技巧，那就是定義了一個(gè)listener 類，它將會(huì)在parse的時(shí)候被回調(diào):
require 'rexml/document'
require 'rexml/streamlistener'
include REXML
class MyListener
include REXML::StreamListener
def tag_start(*args)
puts "tag_start: #{args.map {|x| x.inspect}.join(', ')}"
end
def text(data)
return if data =~ /^\w*$/ # whitespace only
abbrev = data[0..40] + (data.length > 40 ? "..." : "")
puts " text : #{abbrev.inspect}"
end
end
list = MyListener.new
source = File.new "books.xml"
Document.parse_stream(source, list)
這里介紹一下StreamListener 模塊，這個(gè)模塊它提供了幾個(gè)空的回調(diào)方法，因此你可以為了實(shí)現(xiàn)你自己的功能而覆蓋它.當(dāng)parser 進(jìn)入一個(gè)tag時(shí)，就會(huì)調(diào)用tag_start方法.而text方法也是類似的，他只不過(guò)是當(dāng)讀取到數(shù)據(jù)時(shí)會(huì)被回調(diào),它的輸出是這樣的：
tag_start: "library", {"shelf"=>"Recent Acquisitions"}
tag_start: "section", {"name"=>"Ruby"}
tag_start: "book", {"isbn"=>"0672328844"}
tag_start: "title", {}
text : "The Ruby Way"
.........................................
3 XPath
REXML通過(guò)XPath 類來(lái)提供Xpath的支持. 它也同時(shí)支持DOM-like和SAX-like .還是前面的那個(gè)xml文件，我們使用Xpath可以這樣做：
book1 = XPath.first(doc, "http://book") # Info for first book found
p book1
# Print out all titles
XPath.each(doc, "http://title") { |e| puts e.text }
# Get an array of all of the "author" elements in the document.
names = XPath.match(doc, "http://author").map {|x| x.text }
p names
輸出是類似于下面的：
book isbn='0672328844'> ... />
The Ruby Way
The Case for Mars
First Man: The Life of Neil A. Armstrong
["Hal Fulton", "Robert Zubrin", "James R. Hansen"]
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