clj-xmltojson

Summary

Makes XML feel a bit more like json.

Given a defined variable called xml with content such as this:

<CATALOG>
  <CD>
    <TITLE>Empire Burlesque</TITLE>
    <ARTIST>Bob Dylan</ARTIST>
    <COUNTRY>USA</COUNTRY>
    <COUNTRY>UK</COUNTRY>
    <COMPANY>Columbia</COMPANY>
    <PRICE>10.90</PRICE>
    <YEAR>1985</YEAR>
  </CD>
  <CD>
    <TITLE>Hide your heart</TITLE>
    <ARTIST>Bonnie Tyler</ARTIST>
    <COUNTRY>UK</COUNTRY>
    <COMPANY>CBS Records</COMPANY>
    <PRICE>9.90</PRICE>
    <YEAR>1988</YEAR>
  </CD>
  <CD>
    <TITLE>Greatest Hits</TITLE>
    <ARTIST>Dolly Parton</ARTIST>
    <COUNTRY>USA</COUNTRY>
    <COMPANY>RCA</COMPANY>
    <PRICE>9.90</PRICE>
    <YEAR>1982</YEAR>
  </CD>
</CATALOG>

provides the parse function, enabling processing like this:

(require '[xmltojson.xmltojson :refer [parse]])
(parse (clojure.data.xml/parse-str xml) {:force-list #{:COUNTRY}})

yielding output such as this:

{:CATALOG
 {:CD
  [{:COMPANY "Columbia",
    :ARTIST "Bob Dylan",
    :PRICE "10.90",
    :YEAR "1985",
    :TITLE "Empire Burlesque",
    :COUNTRY ["USA" "UK"]}
   {:COMPANY "CBS Records",
    :ARTIST "Bonnie Tyler",
    :PRICE "9.90",
    :YEAR "1988",
    :TITLE "Hide your heart",
    :COUNTRY ["UK"]}
   {:COMPANY "RCA",
    :ARTIST "Dolly Parton",
    :PRICE "9.90",
    :YEAR "1982",
    :TITLE "Greatest Hits",
    :COUNTRY ["USA"]}]}}

Note, clojure.data.xml needs to be added to your project deps, or you can use clojure.xml and coerce the xml string into an input stream:

(parse (->  xml .getBytes java.io.ByteArrayInputStream. clojure.xml/parse)
       {:force-list #{:COUNTRY}})

Why

In python systems I’ve made a lot of use of xmltodict , specifically the parse function and arguments such as force_list.

xmltojson.xmltojson/parse aims to do the same (similar?) activity with options force-list, and strip-whitespace?.

Testing

Maybe the interesting part of this is how I’ve tested the python module as compared to the clojure code.

In dev-resources I have build-jython.sh that pulls jython2.7 standalone, compiles xmltodict.py, and zips the newly created class back into the jython jar file. You’ll need jython installed and on your path as well.

What this allows me to do is create a python context and run things directly in jython, from clojure.

So, the interop story isn’t great; I was trying to cast (specifically) clojure types via java into python objects for jython use… but eventually gave up on that and basically just did the interop through json file serialization.

I’d also tinkered with graalvm but eventually decided this was too cumbersome at the moment, especially on getting the virtual environment and xmltodict installed from pypy (and accessible from clojure, with a correct python path.)

I also thought about potentially running a socket repl in python with data interchange via edn… not sure how feasible this would be.

I’m also not sure if any of these things would be performant.

Anyway, as a hack it appears to work with dumping json to a temp file…

Performance

clojure.data.xml should be able to feed a stream to the application, but I’m not exactly sure how performance does at this point and if everything is lazy.

next

• [ ] lazy eval maybe.
• [X] get force list to work
• [ ] add postprocessor functionality, like xmltodict
• [ ] unparse and round-tripping
• [ ] reitit/muuntaja formatter example for http coercion.