Moxieapps file uploader for GWT adding multiple up

The GWT web app I'm building has a page where users can upload CSV files. The upload code uses the Moxieapps GWT Uploader, which mostly works great.

However, I've discovered a strange scenario, where navigating away from the page and back to it adds the upload button again. So the third time I visit the page, the upload section will look like this:

And the relevant part of the generated HTML viewed in an inspector shows that both the input and the div containing the "button" get added over and over (though there is only ever one dropzone):

I've gone over my code many times to see whether I was doing something that could be causing this, but haven't found anything. You don't actually manually add the button or the input; this is done automatically by the framework. The fileUploader gets initialised only once (this being GWT client code, I've debugged using the inspector as well as logging statements to the console to confirm this):

fileUploader.setButtonDisabled(true).setFileTypes("*.csv")
    .setUploadURL(getBaseUrl() + "/fileUpload.upload")
    .setButtonText("<span class=\"buttonText\">Select CSV file to upload</span>")
    .setFileSizeLimit(FILE_SIZE_LIMIT)
    .setButtonCursor(CustomUploader.Cursor.HAND)
    .setButtonAction(CustomUploader.ButtonAction.SELECT_FILE)
    .setUploadProgressHandler(new UploadProgressHandler() {...})
    .setUploadSuccessHandler(...)
    // etc. with other handlers

The method setButtonText() is called from a couple of other places, and the text changes as it should, but only on the last button (if there are several). Otherwise, there's nothing in my code that could possibly be adding the button as far as I can tell.

Has anyone else encountered this issue? Is there some property I need to set to prevent this? Could it be a bug in the moxieapps code?

After writing out my question, and adding "Could it be a bug in the moxieapps code?" at the end, I followed up on that suspicion, and it turns out that it is indeed a bug in the org.moxieapps.gwt.uploader.client.Uploader class.

The input and the "select file" button are added in the onLoad() method of that class without a check whether they may have been added already.

It looks like there hasn't been any active development on this framework for some time, so I thought it was time for a custom override version. I've tested this and it works:

package yourpackagename.client.override;

import java.util.Iterator;

import org.moxieapps.gwt.uploader.client.Uploader;

import com.google.gwt.user.client.ui.FileUpload;
import com.google.gwt.user.client.ui.Widget;
import com.google.gwt.user.client.ui.WidgetCollection;

/**
 * The sole reason this class exists is to fix a bug in the moxieapps uploader
 * (org.moxieapps.gwt.uploader-1.1.0.jar) where it adds a new upload input and
 * button each time its <code>onLoad()</code> method is called, i.e. every time
 * you navigate away from the page and then back to it.
 */
public class CustomUploader extends Uploader {
    @Override
    protected void onLoad() {
        boolean hasFileUploadAlready = false;
        WidgetCollection children = getChildren();
        for (Iterator<Widget> iterator = children.iterator(); iterator.hasNext();) {
            Widget eachWidget = iterator.next();
            if (eachWidget instanceof FileUpload) {
                hasFileUploadAlready = true;
            }
        }
        // Only call the super method if there isn't already a file upload input and button
        if (!hasFileUploadAlready) {
            super.onLoad();
        }
    }
}

Instead of referencing the org.moxieapps.gwt.uploader.client.Uploader, I've changed the references to point to my custom uploader class, which will now check for an existing FileUpload child widget, and simply skip the original onLoad() code if it finds such a widget.

Might be a bit of a crowbar approach, but it works (and in my case, changing the maven-managed JAR file is not very practical). Hopefully, this will be useful to anyone else coming across this problem.