Download file jsf 2.2 primefaces

I'm trying to make use of the p:fileDownload component of primefaces.

<p:commandButton value="Download" ajax="false" icon="ui-icon-arrowthick-1-s">
       <p:fileDownload value="#{fileDownloadView.file}" />
</p:commandButton>

ManageBean:

@ManagedBean
public class FileDownloadView {

    private StreamedContent file;

    public FileDownloadView() {        
        InputStream stream = ((ServletContext)FacesContext.getCurrentInstance().getExternalContext().getContext()).getResourceAsStream("C:\Users\Yo\Desktop\excel.xlsx");
        file = new DefaultStreamedContent(stream, "application/vnd.ms-excel", "docu.xlsx");
    }

    public StreamedContent getFile() {
        return file;
    }
}

The problem is in the line InputStream stream... I have debugged it and I get null . I've also tried as specified in primefaces.org :

InputStream stream = FacesContext.getCurrentInstance().getExternalContext().getResourceAsStream("C:\Users\yo\Excel.xlsx");

Do you know what the reason may be?