Following example shows how to use an AJAX request to refresh some components and at the same time make the browser ask back for a file to be downloaded.

We start with a WebMarkupContainer that is at the same time an IResourceListener

import org.apache.wicket.IResourceListener;
import org.apache.wicket.markup.html.WebMarkupContainer;


/**
 * @author  Ernesto Reinaldo Barreiro ([email protected])
 *
 */
public class DocumentResourceListener extends WebMarkupContainer implements IResourceListener 
{
	private static final long serialVersionUID = 1L;
	
	
	private IResourceListener resourceListener;

	/**
	 * Constructor receiving an IResourceListener..
	 * 
	 * @param id
	 * @param resourceListener
	 */
	public DocumentResourceListener(final String id, IResourceListener resourceListener)
	{
		super(id);
		this.resourceListener = resourceListener;
	}

	/**
	 * Gets the url to use for this link.
	 * 
	 * @return The URL that this link links to
	 */
	protected CharSequence getURL()
	{
		return urlFor(IResourceListener.INTERFACE);
	}

	

	@Override
	protected boolean getStatelessHint()
	{	
		return false;
	}
	
	public void onResourceRequested() {
		this.resourceListener.onResourceRequested();
	}
}

Next step is to define DynamicWebResource that will serves a "test.pdf" PDF file taken from the resources.

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

import org.apache.wicket.markup.html.DynamicWebResource;
import org.apache.wicket.protocol.http.WebResponse;

/**
 * @author  Ernesto Reinaldo Barreiro ([email protected])
 *
 */
public class MyPdfResource extends DynamicWebResource {

	private static final long serialVersionUID = 1L;

	static int BUFFER_SIZE = 10*1024;
	
	/**
	 * 
	 */
	public MyPdfResource() {
	}

	/* (non-Javadoc)
	 * @see org.apache.wicket.markup.html.DynamicWebResource#getResourceState()
	 */
	@Override
	protected ResourceState getResourceState() {
		return new ResourceState() {
			
			@Override
			public String getContentType() {
				return "application/pdf";
			}
			
			@Override
			public byte[] getData() {
				try {
					return bytes(MyPdfResource.class.getResourceAsStream("test.pdf"));
				} catch (Exception e) {
					return null;
				}
			}
		};
	}
	
	public static  byte[] bytes(InputStream is) throws IOException {
		ByteArrayOutputStream out = new ByteArrayOutputStream();
		copy(is, out);
		return out.toByteArray();
	}
	
	@Override
	protected void setHeaders(WebResponse response) {
		super.setHeaders(response);
		response.setAttachmentHeader("test.pdf");
	}
	
	public static void copy(InputStream is, OutputStream os) throws IOException {
		byte[] buf = new byte[BUFFER_SIZE];
		while (true) {
			int tam = is.read(buf);
			if (tam == -1) {
				return;
			}
			os.write(buf, 0, tam);
		}
	}
}

One important bit here is the line response.setAttachmentHeader("test.pdf");. Otherwise current page will be replaced instead of browser a "Do you want to download file" window.

Then we have the page where the "trick" is performed:

import org.apache.wicket.ajax.AjaxRequestTarget;
import org.apache.wicket.ajax.markup.html.AjaxLink;
import org.apache.wicket.markup.html.WebPage;
import org.apache.wicket.markup.html.basic.Label;
import org.apache.wicket.model.AbstractReadOnlyModel;


/**
 * @author  Ernesto Reinaldo Barreiro ([email protected])
 *
 */
public class TestPage extends WebPage{

	private Label text;
	
	private String labelText = "Hi!";
	
	private DocumentResourceListener documentResourceListener;

	
	/**
	 * 
	 */
	public TestPage() {
		
		AjaxLink<Void> link = new AjaxLink<Void>("link") {
			
			private static final long serialVersionUID = 1L;

			@Override
			public void onClick(AjaxRequestTarget target) {
				TestPage.this.labelText = "Hi! and donwload a file!";
				if(target!= null) {
					target.addComponent(TestPage.this.text);
					String url = ""
					target.appendJavascript(";window.location.href='';");
				}
			}
		};
		
		add(link);
		text = new Label("text", new AbstractReadOnlyModel<String>() {
			
			private static final long serialVersionUID = 1L;

			@Override
			public String getObject() {
				return TestPage.this.labelText;
			}
		});
		text.setOutputMarkupId(true);
		add(text);
		
		documentResourceListener = new DocumentResourceListener("listener", new MyPdfResource());
		
		add(documentResourceListener);
	}

}

The trick is just the lines:

                        @Override
			public void onClick(AjaxRequestTarget target) {
				TestPage.this.labelText = "Hi! and donwload a file!";
				if(target!= null) {
					target.addComponent(TestPage.this.text);
					String url = ""
					target.appendJavascript(";window.location.href='';");
				}
			}

This will make the browser send back a request to documentResourceListener component who will then stream
back the resource.

And for sake of completeness the HTML of the TestPage page:

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
   "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns:wicket="org.apache.wicket">
	<head>
	</head>
	<body>
		<a wicket:id="link">Click Me</a>	
		<span wicket:id="text"></span>	
		<div wicket:id="listener"></div>
	</body>
</html>

Note: I have tested this with FF-3.5, IE-7 and Chrome. I hope it works fine with other browsers, browser-versions, as well!

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[CONF] Apache Wicket > AJAX update and file download in one blow

AJAX update and file download in one blow

Page edited by Ernesto Reinaldo Barreiro

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