How to download a XML dynamic-generated file in JSF?

Question

In the JSF page I have:

<p:commandButton value="Download" action="#{myMBean.downloadXMLFile}" />

In the MBean I have the following (try/catch ommited):

public void downloadXMLFile() {

String xml = this.getXML();//returns the whole XML but in String format.
HttpServletResponse response = (HttpServletResponse) FacesContext.getCurrentInstance().getExternalContext().getResponse();  
response.setContentType("text/xml");
response.setHeader("Content-Disposition", "attachment;filename=file.xml");  

ServletOutputStream out = response.getOutputStream();
out.write(xml.getBytes());  
out.flush(); 
}

But when I run it, I get an IllegalStateException:

java.lang.IllegalStateException: setBufferSize() called after first write to Output Stream/Writer

I tried also to convert the XML String to a Document and converting it to a File but got the same error. is it really necessary in order to work?

Answer 1

The error occurs because of an attempt to render your response during the JSF render phase.

You are using a raw response object obtained via ExternalContext, and writing the response yourself. You must tell the JSF runtime that the response is complete so it doesn't attempt to process it.

Save a reference to your FacesContext:

FacesContext ctx = FacesContext.getCurrentInstance();
HttpServletResponse response = (HttpServletResponse) ctx.getExternalContext().getResponse();
...

and call responseComplete() when you finish building your response:

ctx.responseComplete();