Ruby程序中创建和解析XML文件的方法

admin Ruby

2023-12-05 0 242

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

这里要注意的是xml中的属性和值被表示为一个hash，因此我们能够通过attributes[]来提取我们需要的值，元素的值还能通过类似于path的字符串或者整数来取得.其中用整数取的话，是1-based而不是0-based.

2 Stream Parsing（也就是SAX-like Parsing)

这边使用了一个小技巧，那就是定义了一个listener 类，它将会在parse的时候被回调:

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)

这里介绍一下StreamListener 模块，这个模块它提供了几个空的回调方法，因此你可以为了实现你自己的功能而覆盖它.当parser 进入一个tag时，就会调用tag_start方法.而text方法也是类似的，他只不过是当读取到数据时会被回调,它的输出是这样的：

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通过XPath 类来提供Xpath的支持. 它也同时支持DOM-like和SAX-like .还是前面的那个xml文件，我们使用Xpath可以这样做：

book1 = XPath.first(doc, \”//book\”) # Info for first book found
p book1

# Print out all titles
XPath.each(doc, \”//title\”) { |e| puts e.text }

# Get an array of all of the \”author\” elements in the document.
names = XPath.match(doc, \”//author\”).map {|x| x.text }
p names

输出是类似于下面的：

<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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