wicket provide file for download

Question

I have a panel with a submit button. onsubmit, i want to write some text to a file and provide the file for download to the user. Not sure how to go about doing it. If someone can point to a link or code that will really help

Answer 1

This did not end up being easy. I used the download link, but none of the form variables were getting used by download link as clicking on the download link does not submit the form. it just uses initial values. I had to use ajax onchange event to update the instance variables representing the form components and then use the download link to create a file based on user inputs.

Answer 2

As detailed in an entry on the Wicket wiki you need to create a behaviour that constructs your file which is then triggered from a submit link. This will ensure that the model update is complete before you use it in creation of the file.

A Behavior implementation that creates a request from a resource stream:

public abstract class AJAXDownload extends AbstractAjaxBehavior
{
    private boolean addAntiCache;

    public AJAXDownload() {
        this(true);
    }

    public AJAXDownload(boolean addAntiCache) {
        super();
        this.addAntiCache = addAntiCache;
    }

    /**
     * Call this method to initiate the download.
     */
    public void initiate(AjaxRequestTarget target)
    {
        String url = getCallbackUrl().toString();

        if (addAntiCache) {
            url = url + (url.contains("?") ? "&" : "?");
            url = url + "antiCache=" + System.currentTimeMillis();
        }

        // the timeout is needed to let Wicket release the channel
        target.appendJavaScript("setTimeout(\"window.location.href='" + url + "'\", 100);");
    }

    public void onRequest()
    {
        ResourceStreamRequestHandler handler = new ResourceStreamRequestHandler(getResourceStream(),getFileName());
        handler.setContentDisposition(ContentDisposition.ATTACHMENT);
        getComponent().getRequestCycle().scheduleRequestHandlerAfterCurrent(handler);
    }

    /**
     * Override this method for a file name which will let the browser prompt with a save/open dialog.
     * @see ResourceStreamRequestTarget#getFileName()
     */
    protected String getFileName()
    {
        return null;
    }

    /**
     * Hook method providing the actual resource stream.
     */
    protected abstract IResourceStream getResourceStream();
}

The (submit)link and behavior implementation:

final AJAXDownload download = new AJAXDownload()
{
    @Override
    protected IResourceStream getResourceStream()
    {
        return createResourceStream(item.getModelObject());
    }
};
item.add(download);

item.add(new AjaxSubmitLink("link") {
    @Override
    public void onSubmit(AjaxRequestTarget target, Form<?> form)
    {
        // do whatever with the target, e.g. refresh components
        target.add(...);

        // finally initiate the download
        download.initiate(target);
    }
});

@magomi created a similar implementation in response to this question.