Ruby程序中创建和解析XML文件的方法

使用builder创建XML

builder安装方法：

gem install builder

require 'builder'  
 
x = Builder::XmlMarkup.new(:target =>
 $stdout, :indent => 1) 
#":target =＞$stdout"参数：指示输出内
容将被写向标准输出控制台 
#":indent =＞1"参数：XML输出形式将被缩
进一个空格字符x.instruct! :xml,
:version =>'1.1',:encoding => 'gb2312' 
x.comment! "书本信息" 
 
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创建XML输出结果：

< ?xml version="1.1" encoding="gb2312"?> 
< !-- 书本信息 --> 
< 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 是一个完全用ruby写的processor ,他有多种api，其中两个经典的api是通过DOM-like 和SAX-like 来进行区分的。第一种是将整个文件读进内存，然后存储为一个分层的形式(也就是一棵树了).而第二种是"parse as you go",当你的文件很大，并且内存受到限制的时候，比较适合用这种。

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)

我们需要require rexml/document 库，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 

								 
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