Form Field Values, Multipart Forms and Servlets (... oh my)

I saw an intriguing question on stackoverflow yesterday, by Tony Petruzzi .  It was about parsing form field values, but with a bit of twist. We all know that when multiple form fields have the same name, the field values are returned as a comma delimited list in CF. While that is a handy feature at times, what do you do when the field values contain commas? Well after a few false starts, I did come up with one option, but wanted to describe it in a little more detail than stackoverflow comments allow.

Stealing from Tony's example, take the simple form below. Each of the two fields contains a different number of letters separated by a comma. But once the form is submitted, the value is just one big csv string. So you really have no way of determining which values were actually entered into each of the fields.

Tony's post described a slick method of extracting the field values as a string array, with the help of getPageContext() and getParameterMap(). The problem was it does not seem to work when the enctype is multipart/form-data.

<cfdump var="#getPageContext().getRequest().getParameterMap()#">

From what little I have read so far, my understanding of the issue is that the standard request object (ie HttpServletRequest) does not handle multipart requests.  A special multipart handler is needed instead. So with that in mind, my next question was what handler does CF use?

Well, while poking around in the CF libraries a while back, I noticed CF uses some of the O'Reilly servlet classes. In particular, the ones for MultiPartRequest handling. If you look at the API you will notice the classes return all sorts of good information like input field names, values, etcetera. So I figured that is probably what CF was using for the form and that this information had to be exposed ...somewhere.

On a whim I decided to get back to basics and dump the FORM scope class. That revealed a promising method named getPartsArray(). Looping through the array confirmed my suspicion that results were indeed one of the O'Reilly classes:
com.oreilly.servlet.multipart.ParamPart

<cfset formClass = createObject("java", form.getClass().name)>
   <cfdump var="#formClass#" label="FORM Scope Class" />
   
   <cfloop array="#form.getPartsArray()#" index="part">
      <cfdump var="#part#" label="Part Element" />
   </cfloop>

All that was left was to use a few methods from the API to the retrieve the form field information. First the isParamPart() method is used to identify the input fields only. Then getName() and getStringValue() are used to grab the field's name and value.  As you can see, there is not much to it.

<!--- if this is a multipart request ...--->
   <cfset variables.parts = form.getPartsArray()>
   <cfif structKeyExists(variables, "parts")>
      <cfoutput>   
      <cfloop array="#variables.parts#" index="p">
         <cfif p.isParam()>
            isParam() = #p.isParam()#
            getName() = #p.getName()#
            stringValue() = #p.getStringValue()#
         </cfif>
      </cfloop>
      </cfoutput>
   </cfif>

Of course this only applies to multipart requests. The part array will be null for other request types. So make sure the array exists before using it. Anyway, I thought this was an interesting approach to the old form field dilemma. But if anyone knows of any other techniques, I would love to hear them.