DZone Snippets: xml code

Adding helpful error messages to your Ruby code

jrobertson (James Robertson) — Wed, 30 Apr 2008 11:40:47 GMT

This Ruby code raises an error if the XPath query fails because the attribute being queried did not exist for the given element.



  def map_pattr(node, fieldx, valuex)

    begin

    parameter = node.root.elements["parameter[@field='#{fieldx}']"]

    parameter.add_attribute('value', valuex)

    parameter

    

    rescue

      puts 'feedpopulated.rb: map_attr() the field ' + fieldx + ' was not found in params.'

      raise

    end

  end

Notice that a raise statement is used to ensure that the system error message is raised and any further code execution is halted.

Without adding a customized helpful message I would be left scratching my head trying to work out what the following system error message meant.



./feedpopulated.rb:27:in `map_pattr': undefined method `add_attribute' for nil:NilClass (NoMethodError)

     from ./feedpopulated.rb:51:in `create_record'

     from ./feedpopulated.rb:49:in `each'

     from ./feedpopulated.rb:49:in `create_record'

     from ./recordx.rb:91:in `call_create'

     from ./s3fileuploader_handler.rb:14:in `call'

     from ./s3fileuploader_handler.rb:40:in `invoke'

     from ./uploadtwitteraudio.rb:22:in `initialize'

     from /usr/lib/ruby/1.8/rexml/element.rb:890:in `each'

     from /usr/lib/ruby/1.8/rexml/xpath.rb:53:in `each'

     from /usr/lib/ruby/1.8/rexml/element.rb:890:in `each'

     from ./uploadtwitteraudio.rb:18:in `initialize'

     from ./uploadtwitteraudio.rb:72:in `new'

     from ./uploadtwitteraudio.rb:72

Reference: Programming Ruby: The Pragmatic Programmer's Guide - Exceptions, Catch, and Throw [ruby-doc.org]

Helpful XPath examples

jrobertson (James Robertson) — Tue, 29 Apr 2008 23:34:28 GMT

A few XPath examples copied from XPath Syntax [w3schools.com]

Predicates



/bookstore/book[1] 	# Selects the first book element that is the child of the bookstore element. 

                        # Note: IE5 and later has implemented that [0] should be the first node, 

                        # but according to the W3C standard it should have been [1]!!

/bookstore/book[last()] 	# Selects the last book element that is the child of the bookstore element

/bookstore/book[last()-1] 	# Selects the last but one book element that is the child of the bookstore element

/bookstore/book[position()<3] 	# Selects the first two book elements that are children of the bookstore element

//title[@lang] 	# Selects all the title elements that have an attribute named lang

Selecting Unknown Nodes



/bookstore/* 	# Selects all the child nodes of the bookstore element

//* 	# Selects all elements in the document

//title[@*] 	# Selects all title elements which have any attribute

Selecting Several Paths



//book/title | //book/price  	# Selects all the title AND price elements of all book elements

Using ruby to upload multiple files to Amazon S3

jrobertson (James Robertson) — Sat, 26 Apr 2008 14:17:58 GMT

This ruby code builds upon the code S3 upload client for Ruby [dzone.com] by reading the account details and file details from XML files.



#!/usr/bin/env ruby

#file : rubys3file2upload.rb



require 'rubygems'

require 'aws/s3'

require 'rexml/document'

include REXML



class S3FileUpload



  def initialize(xml_accounts_file, xml_upload_file)

    initialize_account(xml_accounts_file)

    main(xml_upload_file)

  end



  def initialize_account(accounts_file)



    file = File.new(accounts_file)

    doc = Document.new(file)



    account = doc.root.elements['records/access']

    h = Hash.new

    h[:access_key_id] = account.elements['key_id'].text.to_s

    h[:secret_access_key] = account.elements['secret'].text.to_s

    AWS::S3::Base.establish_connection!(h)



  end



  def main(xml_upload_file)

    file = File.new(xml_upload_file)

    doc = Document.new(file)

puts doc

    doc.root.elements.each('records/file') do |f|

      local_file = f.elements['local'].text.to_s

      bucket = f.elements['bucket'].text.to_s

      mime_type = f.elements['mime_type'].text.to_s

      upload(local_file, mime_type, bucket)

    end

  end



  def upload(local_file, mime_type, bucket)



    base_name = File.basename(local_file)



    puts "Uploading #{local_file} as '#{base_name}' to '#{bucket}'"



    AWS::S3::S3Object.store(

      base_name,

      File.open(local_file),

      bucket,

      :content_type => mime_type,

      :access => :public_read

    )



    puts "Uploaded!"

  end



end



if __FILE__ == $0

  s3fu = S3FileUpload.new('s3accounts.xml', 's3files2upload.xml')

end

file: s3accounts.xml



  

    REPLACE_MEREPLACE_MEREPLACE_ME

file: s3files2upload.xml



  

    

      autocomplete.html

      t2000

      text/html

    

    

      autocomplete2.html

      t2000

      text/html

    

    

      autocomplete3.html

      t2000

      text/html

Note: The file given the correct permission could be read from http://t2000.s3.amazonaws.com/autocomplete.html

Reference: http://amazon.rubyforge.org/

Adding style to SVG

jrobertson (James Robertson) — Fri, 18 Apr 2008 21:37:11 GMT

To reference a CSS file within an SVG file refer to the following example code.

Here's what an SVG CSS file looks like.



.str1 {stroke:#0093DD;stroke-width:16;color:#0093DD}

.str2 {stroke:#0093DD;stroke-width:12}

.str3 {stroke:#0093DD;stroke-width:10}

.str4 {stroke:#0093DD;stroke-width:6}



.str0 {stroke:#DA251D;stroke-width:55;color:#DA251D}

.str6 {stroke:#BB90BB;stroke-width:44;color:#BB90BB}

.str5 {stroke:#0093DD;stroke-width:4}

.str7 {stroke:#1F1A17;stroke-width:13}



.fil0 {fill:none}

.fil2 {fill:#1F1A17}

.fil1 {fill:#C4E5FA}

.fil3 {fill:#FFFFFF}

Source: Example for using CSS-Styles [carto.net]
Reference: Styling - SVG 1.1 - 20030114 [w3.org]

Converting text to SVG

jrobertson (James Robertson) — Fri, 18 Apr 2008 18:14:11 GMT

First of all the Ruby code reads the text, splits it into an array and then saves it in XML format.



require 'rexml/document'

include REXML



a = "Open source is a development method for software that harnesses the power of distributed peer 

review and transparency of process. The promise of open source is better quality, higher reliability, 

more flexibility, lower cost, and an end to predatory vendor lock-in.".split(' ') 



doc = Document.new

doc.add_element('text')

oline = Element.new('line')



char_count = 0

a.each do |word|

  

  oword = Element.new('word')

  oword.text = word.to_s

  oword.add_attribute('length',char_count)

  oline << oword 

  char_count += word.length

  

  if char_count > 50

    doc.root << oline

    oline = Element.new('line')

    char_count = 0

  end

end

doc.root << oline

puts char_count

puts doc

Here's a sample of the XML created





  

    Opensourceis

    adevelopmentmethod

    forsoftwarethat

    harnesses

  

  

    thepower

    ofdistributedpeer

    reviewandtransparency

    ofprocess.

  

  

    The

    promiseofopen

    sourceisbetter

    quality,higherreliability,

  

  

    moreflexibility,lower

    cost,andan

    endtopredatory

    vendor

  

  

    lock-in.

The XML is then transformed to SVG using the following XSL file











            method="xml"

            indent="yes"/>

            

  

                      xmlns:xlink="http://www.w3.org/1999/xlink" >

      

        

      

    

  

  

  

    12

    20

The final SVG output [twitxr.com] shows 5 lines of text with each word as a separate SVG text element.

Append an XML element using the append operator

jrobertson (James Robertson) — Thu, 17 Apr 2008 23:50:25 GMT

This Ruby code appends an XML node to an XML document using the append << operator.



      doc2 = Document.new(xml_svg)

      obody.text = ''

      obody << doc2.root

In this example the original obody.text contained escaped xml, which was then initialised as an XML document and appended to obody to be processed as pure XML.

Using XSLT to generate SVG

jrobertson (James Robertson) — Thu, 17 Apr 2008 10:45:36 GMT

This XSL file is intended to be used as an SVG XSL template file which displays SVG content using Gorg (XSLT back-end processor).











            method="xml"

            indent="yes"/>

            

  

                  xmlns:xlink="http://www.w3.org/1999/xlink" >

Reference: 'using XSLT to generate SVG' http://snurl.com/24pwo [carto.net]

Instruct a shared whiteboard to save and refresh

jrobertson (James Robertson) — Thu, 27 Mar 2008 19:14:07 GMT

The following code used with the ProjectX API informs the client web browser that the whiteboard will be refreshed in 5 seconds. It then archives the current whiteboard information, formats it, and sends a message to each web browser to refresh their view.





  

    

      

        ecmascript

        startRefresh(5)

        system

      

    

    

      

        5

      

    

    

      

    

    

      

        ecmascript

        reloadDocument()

        system

*update 1:14am*
The whiteboard demo [rorbuilder.info] allows the user to draw using the mouse within the web browser which renders SVG. Tested on Flock and Firefox.

*update 4:42pm 28 Mar 08*
You can also view the whiteboard message queue [rorbuilder.info].

*update 6:29pm Mar 08*
I've created a short url (http://rubyurl.com/vxHD) (to demonstrate the cleaning of the whiteboard) which redirects to this http://rorbuilder.info/api/projectx.cgi?xml_project=ecmascriptstartRefresh(5)system5ecmascriptreloadDocument()system

I've

Load PRX document and display elements

swhitley (Shannon Whitley) — Tue, 18 Mar 2008 16:59:03 GMT



//Using a simple curl library (not shown) to get xml text

$curl = new CURL();

//$prx contains the url of a PRX document (e.g. http://www.prxbuilder.com/link.aspx?p=1)

$xml = $curl->get($prx);



//Load the XML file

$doc = new DOMDocument();

$doc->loadXML($xml);



//Retrieve specific PRX elements (subheadline, dateline, body)

$subheadline = $doc->getElementsByTagName('subheadline')->item(0)->nodeValue;

$dateline = $doc->getElementsByTagName('dateline')->item(0)->nodeValue;

$body = $doc->getElementsByTagName('body')->item(0)->nodeValue;



//Format and display - apply_filters is a WP function.

$content = ''.$subheadline.'';

$content .= ''.$dateline.'';

$content .= ''.$body.'';

$content = apply_filters('the_content_rss', $content);

$content = str_replace(']]>', ']]>', $content);



echo $content;

Load PRX document and display elements

swhitley (Shannon Whitley) — Tue, 18 Mar 2008 16:57:00 GMT



//Using a simple curl library (not shown) to get xml text

$curl = new CURL();

//$prx contains the url of a PRX document (e.g. http://www.prxbuilder.com/link.aspx?p=1)

$xml = $curl->get($prx);



//Load the XML file

$doc = new DOMDocument();

$doc->loadXML($xml);



//Retrieve specific PRX elements (subheadline, dateline, body)

$subheadline = $doc->getElementsByTagName('subheadline')->item(0)->nodeValue;

$dateline = $doc->getElementsByTagName('dateline')->item(0)->nodeValue;

$body = $doc->getElementsByTagName('body')->item(0)->nodeValue;



//Format and display - apply_filters is a WP function.

$content = ''.$subheadline.'';

$content .= ''.$dateline.'';

$content .= ''.$body.'';

$content = apply_filters('the_content_rss', $content);

$content = str_replace(']]>', ']]>', $content);



echo $content;