Things aren't always groovy in the Grails world.  Grails makes an effort to support many disparate application servers.  Sometimes this all encompassing approach can lead to problems.  This is a "Grails gotcha" I recently ran into.

I'm currently working on an application that requires users to upload files to the server.  Thanks to some good documentation, I was able to get this up and running  quite easily, or so I thought.

In my development environment, which by default utilizes Jetty, everthing ran fine.  The problem didn't appear until I tested the application on Tomcat 6.0.18 which we'll be using in production.  My form code was as follows:

<g:form id="receiptUpload" controller="expenseReport" action="upload" id="${expenseReportId}" method="post" enctype="multipart/form-data">
    <table width="100">
        <tbody>
            <tr>
                <td><label>File:</label></td>
                <td><input type="file" name="image" class="is_required"/></td>
            </tr>
            <tr>
                <td>&nbsp;</td>
                <td class="validFileTypes">
                    jpeg, bmp, png, pnm, tiff, wbmp
                </td>
            </tr>
            <tr>
                <td/>
                <td><input type="submit" value="Upload"/>
                </td>
            </tr>
        </tbody>
    </table>
</g:form>

When the user attempted to upload a file, they were greeted with the following error:

Could not find closure property for URI [/expenseReport/upload/1] for controller [ExpenseReportController]!

Can you spot the cause of the problem?  Initially it's not that obvious.  When I tried to access the controller directly by typing it in the URL, the controller and the closure seemed to be found.  Everything appeared to be coded properly.  Hmmm...dilemmas, dilemmas.

I deployed the same application on Glassfish and it worked!  Okay, the problem was a Tomcat one, but what was the cause?  After some trial and error I found the culprit.  Tomcat does not like it when you include the id attribute in the <g:form> tag!  Notice the url in the error message: "/expenseReport/upload/1".  That URL is formatted improperly for Tomcat.  It should be: "/expenseReport/upload?id=1"

Modifying my form to pass the id in as a hidden field did the trick.  Here's the correct form with modified lines in bold text:

<g:form controller="expenseReport" action="upload" method="post" enctype="multipart/form-data">
    <table width="100">
        <tbody>
            <tr>
                <td><label>File:</label></td>
                <td><input type="file" name="image" class="is_required"/></td>
            </tr>
            <tr>
                <td>&nbsp;</td>
                <td class="validFileTypes">
                    jpeg, bmp, png, pnm, tiff, wbmp
                    <input type="hidden" name="id" value="${expenseReportId}" />
                </td>
            </tr>
            <tr>
                <td/>
                <td><input type="submit" value="Upload"/>
                </td>
            </tr>
        </tbody>
    </table>
</g:form>

Tomcat only choked on the id attribute during file uploads.  It worked as expected in all other scenarios.  In summary, don't use the id attributed in <g:form> tags if you plan on doing any file uploading.  It will only get you into trouble.