Ways to create and parse XML files in Ruby programs _ruby topics

Using Builder to create XML

Builder installation Method:

Gem Install Builder

Require ' builder '  
 
x = builder::xmlmarkup.new (: Target =>
 $stdout,: Indent => 1) 
# ": Target => $stdout" Parameters: Indicates that the output
will be written to the standard output console 
# ": Indent =>1" parameter: The XML output form will be indented
into a space character x.instruct!: XML,
: Version => ' 1.1 ',: Encoding => ' gb2312 ' 
x.comment! Book Info 
 
x.library ("shelf" => "recent acquisitions") { 
x.section ("name" => "Ruby") { 
X.book ("ISBN") => "0672310001") { 
x.title "programming Ruby"  
x.author "Yukihiro" 
x.description "programming Ruby-< C18/>the Pragmatic Programmer ' s Guide '}} 
 

P x #打印XML

Ruby creates XML output results:

< XML version= "1.1" encoding= "gb2312"?> 
<!--book information--> 
< 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> 

Parsing XML using Rexml

Rexml is a processor written entirely in Ruby, with a variety of APIs, two classic APIs that are distinguished by dom-like and sax-like. The first is to read the entire file into memory and then store it as a layered form (that is, a tree). The second is "parse as you Go", which is more appropriate when your files are large and memory is limited.

Look at the following book.xml:

Reference

<library shelf= "recent acquisitions" > <section name= "Ruby" > <book isbn= "0672328844" > <t Itle>the Ruby way</title> <author>hal fulton</author> <description> Second EDI tion. 
      The book is 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> <des 
      Cription>pushing toward a second home for the human race. </description> </book> <book isbn= "074325631X" > <title>first man:the Life of Nei L. armstrong</title> <author>james R. hansen</author> <description>definitive Biog 
      Raphy of the "the" the Moon. </description> </book> </section> </liBrary>
 

1 tree parsing (i.e. dom-like)

We need require rexml/document libraries, and 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 

The note here is that the attributes and values in XML are represented as a hash, so we can extract the values we need through attributes[]. The value of an element can also be obtained by means of a string or an integer similar to path. It is 1-based rather than 0-based, with integers.

2 Stream parsing (i.e. Sax-like parsing)

Here's a little trick that defines a listener class that will be called back at parse:

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 to 
  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) 

Here's an introduction to the Streamlistener module, which provides a few empty callback methods, so you can override it to achieve your own functionality. When parser enters a tag, it calls Tag_ The Start method. And the text method is similar, he only is when reads the data to be recalled, its output is this:

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 provides XPath support through an XPath class. It also supports Dom-like and sax-like. or the previous XML file, which we use XPath to do:

Book1 = Xpath.first (Doc, "//book") # Info for a-i-  found 
p book1 
 
# Print out all titles 
Xpath.each (d OC, "//title") {|e| puts e.text} # Get a array of all of 
 
the ' author ' elements in the document. 
names = Xpath.match (Doc, "//author"). Map {|x| X.text} 
p names 

The output is similar to the following:

<book isbn= ' 0672328844 ' > ... </> the Ruby Way the case for 
Mars 
-A-man:the life of Neil A. Armstrong 
["Hal Fulton", "Robert Zubrin", "James R. Hansen"]