Converting HL7 v2 to JSON

I am looking to convert HL7 v2 (older EDI format) messages to JSON, so I could make them processable under Apache Drill and compressible under Parquet.

I looked into HAPI, but I am not having luck finding utility for non-XML HL7 to JSON conversion.

Does anyone have a suggestion or a reference to a library?

Just use HAPI to convert to XML. The code below requires Saxon, because the XML-to-JSON requires XSLT 2.0, but if you already have a method to convert XML to JSON, then you just need the first two lines, which are entirely HAPI. You should download the XSLT locally for production, of course. :-)

String convertHL7ToJson(Message message) {
    try {
        DefaultXMLParser xmlParser = new DefaultXMLParser(new CanonicalModelClassFactory("2.6"));
        String xml = xmlParser.encode(message);
        Transformer xmlTransformer = TransformerFactory.newInstance("net.sf.saxon.TransformerFactoryImpl", null).newTransformer(
            new StreamSource(new StringReader(readFileFromURL("https://github.com/bramstein/xsltjson/raw/master/conf/xml-to-json.xsl")))
            );
          StringWriter result = new StringWriter();
          xmlTransformer.transform(
             new StreamSource(new StringReader(xml)), new StreamResult(result)
          );
          return result.toString();
    } catch (Throwable t) {
        t.printStackTrace();
    }
    return null;
}

String readFileFromURL(String url) {
    InputStream is = null;
    try {
        return new Scanner(is = new URL(url).openStream(), "UTF-8").useDelimiter("\\A").next();
    } catch (Throwable t) {
        t.printStackTrace();
    } finally {
        if(is != null)
            try {
                is.close();
            } catch (Throwable ignored){}
    }
    return null;
}

This creates output like this:

"ORM_O01":{"MSH":{"MSH.1":"|","MSH.2":"^~\\&","MSH.3":{"HD.1":"TEST"},"MSH.4":{"HD.1":"TEST000","HD.2":"BL"},...