p：fileDownload的发行（例外）

Question

Java代码：

@ManagedBean(name="fileDownloadController")
@ViewScoped
public class MBfileDownloadController {

    private StreamedContent file;
    private List<File>  listfiles=new ArrayList<File>();
    private String fileName;
    private String ruteGluster;

    public MBfileDownloadController() throws NamingException {

        Context context = new InitialContext();
        ruteGluster = (String) context.lookup("java:/util/glusterFS");

        if (ruteGluster.charAt(ruteGluster.length() - 1) != '/') {
            ruteGluster = ruteGluster + "/";
        }

        File filestream=new File(ruteGluster + listfiles);

        try {
            file = new DefaultStreamedContent(new FileInputStream(filestream), new MimetypesFileTypeMap().getContentType(filestream));
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    public List<File> getListfiles() {

        File folder = new File(ruteGluster + "reportesEstaticos/spools");
        File[] listOfFiles = folder.listFiles();
        listfiles=Arrays.asList(listOfFiles);

        for(int i=0;i<listfiles.size();i++){

            listfiles.get(i);
        }

        System.out.println("The List of file are" + listfiles);

        return listfiles;
    }

    public void setListfiles(List<File> listfiles) {

        this.listfiles = listfiles;
    }

    public String getFileName() {

        getListfiles();
        return fileName;
    }

    public void setFileName(String fileName) {

        this.fileName = fileName;
    }

    public StreamedContent getFile() {

        return this.file;
    }
}

xhtml：

<h:dataTable value="#{fileDownloadController.listfiles}" var="x" 
    bgcolor="#F1F1F1" border="10" cellpadding="5" 
    cellspacing="3" first="0" rows="15" width="50%" 
    summary="This is a JSF code to create dataTable.">

<h:column>
   <f:facet name="header">
     <h:outputText value="Spools"></h:outputText>
   </f:facet>

   <h:commandLink value="#{x.name}">
    <i class="fa fa-download" aria-hidden="true" style="width: 20px"></i>
    <p:fileDownload value="#{fileDownloadController.file}" />
  </h:commandLink>

</h:column>

</h:dataTable>

当我执行代码时，出现以下异常，并且不下载文件，但表显示了文件并且表很好。