Validating whether a string is well-formed XML

[dclayne]

I'm trying to come up with a script for a scoped application that will validate whether the content of a string field is well-formed XML. I was thinking I could call the XMLDocument2 object wrapper and use a try/catch scenario to tell me whether the parseXML function worked on the provided XML string. For some reason, the error encountered by badly-formed XML against the XMLDocumentXML2 object cannot be caught within JavaScript.

Script Version 1:

//Good XML string

try{

var xmlString = "<test><one><two att=\"xxx\">abcd1234</two><three boo=\"yah\" att=\"yyy\">1234abcd</three><two>another</two></one><number>1234</number></test>";

var xmlDoc = new XMLDocument2();

xmlDoc.parseXML(xmlString);

gs.info(xmlDoc.toString());

}

catch(err){

gs.info('bad');

}

Script Version 2:

//Bad XML string with <one> missing

try{

var xmlString = "<test><two att=\"xxx\">abcd1234</two><three boo=\"yah\" att=\"yyy\">1234abcd</three><two>another</two></one><number>1234</number></test>";

var xmlDoc = new XMLDocument2();

xmlDoc.parseXML(xmlString);

gs.info(xmlDoc.toString());

}

catch(err){

gs.info('bad');

}

Running the second script in the background script utility doesn't actually capture the error that is encountered when I use parseXML against the badly-formed XML string. Has anyone ever needed to validate XML in a ServiceNow form that's part of a scoped application? Since there is no XML field datatype, and since I'm trying to accomplish this in a scoped application, does anyone have any alternatives for validating whether an XML string is well-formed?

[Troy Riblett]

This is a bit of a hack, but I think something like this may work.

try{

      var xmlString = "<test><two att=\"xxx\">abcd1234</two><three boo=\"yah\" att=\"yyy\">1234abcd</three><two>another</two></one><number>1234</number></test>";

var xmlDoc = new XMLDocument2();

      xmlDoc.parseXML(xmlString);

      if(xmlDoc.toString() == "" && xmlString != ""){

              gs.info('also bad');

      } else{

                  gs.info('good');

        }

}

catch(err){

      gs.info('bad');

}

It looks like if the parse fails that .toString() will return an empty string. The exception is still going to be put in the logs however..

[dclayne]

Thanks, Troy. I wasn't aware the error would always post to the logs. This explains the issue I am seeing. ServiceNow apparently handles the exception in the back-end, so when the XMLDocument2 parsing fails (gs.info(xmlDoc.parseXML(xmlString).toString()), it doesn't trigger the catch scenario in a handled exception. This makes sense now.

It seems like there should be a better approach to determining whether a document is well-formed XML, though, especially since the error cannot be suppressed/handled in the calling script.

[EashVerma]

Hello David,

I tried running your script and apparently, it is working fine in my system. I am using Jakarta instance.

Let me know if you continue to face this issue.

Regards,

Eash Verma

[dclayne]

It looks like we can use xmlDoc.isValid(xmlString) to validate whether the field comprises well-formed XML before actually parsing it. Yay!