JSF file download NullPointerException with View Parameter

Hope I get it straight:

I am trying to create a JSF 2.0 page optimized for mobile use on Tomcat 7. So I am using Mojarra 2.1.6 and PrimeFaces (Core 3.1.1 and Mobile 0.9.1).

My script:

• The user visits a simplified url eg. www.someurl.eu/view.xhtml/12345678
• ServletFilter rewrites url on www.someurl.eu/view.xhtml?id=12345678
• URL parameter is provided for ManagedBean
• The required data is evaluated and published to my view.xhtml
• On my view.xhtml a button is provided to download

My problem:

By clicking the button, the server shows me the NPE when the ManagedBean is set to @RequestScoped. My guess is that a button click starts a new request, my URL parameter is lost and the download file is no longer available. I don't know if I'm right, but if so, I don't know how to solve this graceful one.

My ManagedBean:

@ManagedBean
@RequestScoped
public class ViewBean {

// Elements
...
private StreamedContent file;
...

// Getter and Setter
...
public StreamedContent getFile() {
    invalidateSession();
    return file;
}
public void setFile(StreamedContent file) {
    this.file = file;
}
...

// Init
@PostConstruct
public void init() {

    //read URL-Parameter
    urlSdbac = FacesContext.getCurrentInstance().getExternalContext().getRequestParameterMap().get("id");

    // validate
    if(urlSdbac == null || urlSdbac.equals("") || urlSdbac.length() != 8) {
        urlSdbac = "invalid";
    }
    // get Data
    else {
        SdbCustomerData cd = getFileMetadata(urlSdbac);

        if(cd == null) {
            this.name = "invalid code";
            this.language = "no language options found";
        }
        else {
            ...
            // prepare File for Download
            this.file = new Helper().getWebDavFile(cd.getCid(), cd.getName());
        }
    }
}

      

        
        
        
      

    

My view.xhtml:

<h:form>  
  <pm:page title="Download">
    <pm:view>
        <pm:content>
        ...
            <p:commandButton  value="Download" ajax="false">
                    <p:fileDownload value="#{viewBean.file}" />
            </p:commandButton>
        </pm:content>
    </pm:view>
  </pm:page>
</h:form>

      

        
        
        
      

    

Last but not least, my filter:

@Override
public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException {
    HttpServletRequest request = (HttpServletRequest) req;
    HttpServletResponse response = (HttpServletResponse) res;

    String url = request.getRequestURI();

    Pattern sdbac = Pattern.compile("[A-Za-z0-9]{8}");
    Matcher fit = null;

    // check Page
    if(url.contains("view.xhtml/") && (!url.contains("?id=") && !url.endsWith("view.xhtml")) ) {
        String code = url.substring(url.indexOf("view.xhtml/")+11, url.length());
        // validate Param?
        fit = sdbac.matcher(code);
        if(fit.matches()) {
            // redirect
            response.sendRedirect("/getSDS/view.xhtml?id=" + code);
        }
        else {
            // redirect
            response.sendRedirect("/getSDS/view.xhtml?id=invalid");
        }
    }
    else {
        chain.doFilter(req,res);
    }
} 

      

        
        
        
      

    

My filter matches any URL <url-pattern>/*</url-pattern>

I've also tried setting ManagedBean to @SessionScoped. If I do this, the download is fine, but the user is unable to change the URL due to persistent data in the session managed by the ManagedBean session.

I may be too blind to see the obvious solution.

Any help would be appreciated! Thanks in advance!

PS Exception

java.lang.NullPointerException
org.primefaces.component.filedownload.FileDownloadActionListener.processAction(FileDownloadActionListener.java:58)
javax.faces.event.ActionEvent.processListener(ActionEvent.java:88)
javax.faces.component.UIComponentBase.broadcast(UIComponentBase.java:769)
javax.faces.component.UICommand.broadcast(UICommand.java:300)
javax.faces.component.UIViewRoot.broadcastEvents(UIViewRoot.java:794)
javax.faces.component.UIViewRoot.processApplication(UIViewRoot.java:1259)
com.sun.faces.lifecycle.InvokeApplicationPhase.execute(InvokeApplicationPhase.java:81)
com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101)
com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:118)
javax.faces.webapp.FacesServlet.service(FacesServlet.java:593)
eu.qualisys.getsds.filter.SDBACParamFilter.doFilter(SDBACParamFilter.java:53)