Jython Journeys

Notes about my work with jython and python

Transforming with XSLT on Google AppEngine and jython.

with 7 comments

I’m writing this post in response to a challenge. I wrote a post entitled Jython on Google AppEngine: Why bother?, which was a reply to a statement made by a Google engineer about not seeing the point of running jython on AppEngine. And a similar statement was repeated in a comment on that blog post (i.e. “the gist of what I intended to say was that while it was possible to run Jython on App Engine, I couldn’t think why you’d want to.”)

So rather than get into a back-and-forth of yes-it-is-no-it-isnt-yes-it-is, I thought I’d reply with some simple code that demonstrates something that cannot (currently) be done in cpython on AppEngine, but is easy with jython on AppEngine: XSLT transforms.

So, without further ado, here is the jython source code for running an XSLT transform on Google AppEngine. It is implemented as a jython WSGI application, using xhaus.com’s modjy WSGI gateway for java servlets that was contributed to the jython project a few months back.

In order to get this code running, I suggest you download the modjy on google appengine demo from our downloads site. In that download, there is a jython file called “demo_app.py”. Simply replace the entire contents of that file with the code below, and you’re good to go. If you need help with getting the modjy demo application working on Google AppEngine, see the documentation on the modjy wiki: Running jython WSGI applications on Google AppEngine, with modjy.

__doc__ = """
A demonstration of how to run XSLT transforms on Google AppEngine with jython (not cpython).
Please feel free to use this code in whatever way you wish.
"""
from java.io import StringReader, StringWriter
from javax.xml.transform import Transformer, TransformerFactory
from javax.xml.transform.stream import StreamResult, StreamSource
 
xml_data = """
<books>
  <book>
    <title>2001 - A Space Odyssey</title>
    <author>Arthur C Clarke</author>
  </book>
  <book>
    <title>I, Robot</title>
    <author>Isaac Asimov</author>
  </book>
  <book>
    <title>Kil'n people</title>
    <author>David Brin</author>
  </book>
</books>
"""
 
xslt_source = """
<xsl:stylesheet
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
>
 
<xsl:template match="books">
<html>
  <head><title>A list of books, transformed into html from xml using xslt and jython.</title></head>
  <body>
    <table border="1" width="50%" align="center">
      <caption>A list of books, transformed into html from xml using xslt and jython.</caption>
      <tr><th>Title</th><th>Author</th></tr>
    <xsl:for-each select="book">
      <tr><td><xsl:value-of select="title/text()"/></td><td><xsl:value-of select="author/text()"/></td></tr>
    </xsl:for-each>
    </table>
  </body>
</html>
</xsl:template>
 
</xsl:stylesheet>
"""
 
def generate_html(xml_data, xslt_source):
  transformer = TransformerFactory.newInstance().newTransformer(StreamSource(StringReader(xslt_source)))
  output_buffer = StringWriter()
  transformer.transform(StreamSource(StringReader(xml_data)), StreamResult(output_buffer))
  return output_buffer.buffer.toString()
 
def handler(environ, start_response):
  result = generate_html(xml_data, xslt_source)
  start_response("200 Hoopy", [ ('content-type', 'text/html') ])
  return [result]

Happy Transforming!

Written by alan.kennedy

December 1st, 2009 at 6:42 pm

Posted in google appengine, java, jython

Tagged with , , , ,

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7 Responses to 'Transforming with XSLT on Google AppEngine and jython.'

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  1. Excellent example! After this and your previous post, I will henceforth no longer claim that Jython on App Engine doesn’t provide useful benefits over cpython. ;)

    Nick Johnson

    1 Dec 09 at 7:29 pm

  2. Thanks Nick.

    I’m glad that I’ve been able to illustrate to you the benefits of jython on AppEngine.

    Thanks again for the great talk about AppEngine: it was most informative.

    Regards,

    Alan.

    alan.kennedy

    1 Dec 09 at 7:43 pm

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  6. Thanks for the jython on GAE info. I am using GAE python and slowly checking it out a jython version. The startup time is an issue, but I think GOOG will fix it. It’s an interesting engineering problem. :)
    How can I use django templates on GAE jython? Have you written this up somewhere? I searched this site, no luck. Thanks!
    ~Tim

    twitter/waveforms

    6 Jan 10 at 3:14 pm

  7. Sorry, I haven’t written that up; maybe in the future.

    I suggest that you ask your question on the “Django-On-Jython” google group.

    http://groups.google.com/group/django-jython-dev/topics

    Alan.

    alan.kennedy

    11 Jan 10 at 12:39 pm

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