Link to download a zip file in JSF - jsf

Question

I have a zip file in the server. I would like to download that file on click of a link.
Is there a way to create a link to download the zip file in JSF or PrimeFaces, like below HTML5 download attribute in client side?
<a href="/images/myw3schoolsimage.jpg" download>

Answer 1

The HTML5 download attribute has got nothing to do with it. It just allows you to specify an alternate filename which should appear in Save As dialog.
E.g.
<a href="foo.zip" download="bar.zip" />
will show the Save As dialog with bar.zip as filename, but actually provide content of foo.zip. Do note that the bar.zip doesn't necessarily need to exist in server.
As to your concrete problem, there are several ways of serving a file download in a JSF web application.
Just put that file in public web content folder.
WebContent
|-- META-INF
|-- WEB-INF
|-- files
| `-- foo.zip
|-- page.xhtml
:
Then you can refer it as:
download foo.zip
Or, if it's an external folder and you can't move it into public web content, then just tell the server to publish it. E.g. when you have all those files in /path/to/files path and you're using Tomcat server, then add the following into <Host> element of Tomcat's /conf/server.xml:
<Context docBase="/path/to/files" path="/files" />
Then you can refer it as:
download foo.zip
Or, if you have no control over server configuration somehow, or can't figure the server-specific way of publishing an arbitrary folder as a new web context, or it represents a temporary storage folder which you'd rather not publish into web, then create a web servlet which does the job. Leaving caching and resume outside consideration, it's as simple as:
#WebServlet("/files/*")
public class FileServlet extends HttpServlet {
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
String filename = request.getPathInfo().substring(1);
File file = new File("/path/to/files", filename);
response.setHeader("Content-Type", getServletContext().getMimetype(filename));
response.setHeader("Content-Length", String.valueOf(file.length()));
response.setHeader("Content-Disposition", "attachment; filename=\"" + filename + "\"");
Files.copy(file.toPath(), response.getOutputStream());
}
}
You can refer it the same way as #1:
download foo.zip

Answer 2

Though this is an old question, I would like to add this to #BalusC's answer for completeness (coudn't comment due to low reputation): The third solution by #BalusC ( with #WebServlet) can lead to 'Path Traversal Attack', if copy pasted as is.
You may try the attack(for Linux server) using URL:
<yourApplicationURLUntilContextPath>/files/%C0%AE/%C0%AE/%C0%AE/%C0%AE/%C0%AE/%C0%AE/%C0%AE/%C0%AE/%C0%AE/%C0%AE/etc/passwd
There are various solutions to this problem. One being, add the below check before copying the file to output stream:
if(!file.getAbsolutePath().equals(file.getCanonicalPath()))
{
response.sendError(404);
}
You may refer the link for more solutions to path traversal attack.
Hope it helps some developer...