使用builder創建XML
builder安裝方法：
gem install builder
require 'builder' x = Builder::XmlMarkup.new(:target => $stdout, :indent => 1) #":target =＞$stdout"參數：指示輸出內容將被寫向標準輸出控制臺 #":indent =＞1"參數：XML輸出形式將被縮進一個空格字符x.instruct! :xml,:version =>'1.1',:encoding => 'gb2312' x.comment! "書本信息" 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創建XML輸出結果：
< ?xml version="1.1" encoding="gb2312"?> < !-- 書本信息 --> < 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 是一個完全用ruby寫的processor ,他有多種api，其中兩個經典的api是通過DOM-like 和SAX-like 來進行區分的。第一種是將整個文件讀進內存，然后存儲為一個分層的形式(也就是一棵樹了).而第二種是"parse as you go",當你的文件很大，并且內存受到限制的時候，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，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hash，因此我們能夠通過attributes[]來提取我們需要的值，元素的值還能通過類似于path的字符串或者整數來取得.其中用整數取的話，是1-based而不是0-based.
2 Stream Parsing（也就是SAX-like Parsing)
這邊使用了一個小技巧，那就是定義了一個listener 類，它將會在parse的時候被回調:
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，這個模塊它提供了幾個空的回調方法，因此你可以為了實現你自己的功能而覆蓋它.當parser 進入一個tag時，就會調用tag_start方法.而text方法也是類似的，他只不過是當讀取到數據時會被回調,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XPath 類來提供Xpath的支持. 它也同時支持DOM-like和SAX-like .還是前面的那個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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