extracting information from a JSON file using XSLT

Question

I'm a noobie to stackoverflow and xslt so I hope I don't sound unintelligent!

So I am working with SDI for a GIS company and I have a task that requires me to convert points that are in one spacial reference system (SRS) coordinate plane, such as EPSG:4035, to the world SRS, aka EPSG:4326. This really isn't a problem for me since I have the accessibility of an online service that will just give me what I want. However, the format that it outputs is in either JSON or HTML. I have browsed for a while to find a way to extract information from a JSON file but most of the techniques I have seen use xslt:stylesheet version 2.0, and I have to use version 1.0. One method I thought about doing was using the document($urlWithJsonFormat) xslt function, however this only accepts xml files.

Here is an example of the JSON formatted file that I would retrieve after asking for the conversion:

{
  "geometries" : 
  [{
      "xmin" : -4, 
      "ymin" : -60, 
      "xmax" : 25, 
      "ymax" : -41
    }
  ]
}

All I simply want are the xmin, ymin, xmax, and ymax values, that's all! It just seems so simple yet nothing works for me...

Answer 1

You could use an external entity to include the JSON data as part of an XML file that you then transform.

For instance, assuming the example JSON is saved as a file called "geometries.json" you could create an XML file like this:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE wrapper [
<!ENTITY otherFile SYSTEM "geometries.json">
]>
<wrapper>&otherFile;</wrapper>

And then transform it with the following XSLT 1.0 stylesheet:

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
    <xsl:output omit-xml-declaration="yes" indent="yes"/>

<xsl:template match="wrapper">
    <geometries>
        <xsl:call-template name="parse-json-member-value">
            <xsl:with-param name="member" select="'xmin'"/>
        </xsl:call-template>
        <xsl:call-template name="parse-json-member-value">
            <xsl:with-param name="member" select="'ymin'"/>
        </xsl:call-template>
        <xsl:call-template name="parse-json-member-value">
            <xsl:with-param name="member" select="'xmax'"/>
        </xsl:call-template>
        <xsl:call-template name="parse-json-member-value">
            <xsl:with-param name="member" select="'ymax'"/>
        </xsl:call-template>
    </geometries>
</xsl:template>

    <xsl:template name="parse-json-member-value">
        <xsl:param name="member"/>
        <xsl:element name="{$member}">
            <xsl:value-of select="normalize-space(
                                    translate(
                                        substring-before(
                                            substring-after(
                                                substring-after(.,
                                                    concat('&quot;', 
                                                           $member, 
                                                          '&quot;'))
                                                , ':')
                                            ,'&#10;')
                                    , ',', '')
                                  )"/>
        </xsl:element>
    </xsl:template>
</xsl:stylesheet>

To produce the following output:

<geometries>
   <xmin>-4</xmin>
   <ymin>-60</ymin>
   <xmax>25</xmax>
   <ymax>-41</ymax>
</geometries>

Answer 2

The two main choices here seem to be:

1. write (or use) a JSON parser in XSLT 1.0, or
2. use some other language than XSLT.

Since XSLT 1 engines generally can't process JSON directly I'd recommend using some other language to convert to XML.

https://github.com/WelcomWeb/JXS may help you too, if this is XSLT in a Web browser.