p：fileupload在第一次浏览时不会调用监听器？

Question

我发现它真的很奇怪我不知道为什么但是当我第一次选择一个图像时它不会调用上传监听器，但是在第二次选择时它会完美地工作。

查看代码：

<h:form enctype="multipart/form-data;charset='UTF-8'">
    <p:fileUpload id="clientProfile" auto="true" sizeLimit="2097152" allowTypes="/(\.|\/)(gif|jpe?g|png)$/" fileUploadListener="#{clientController.uploadListener}" mode="advanced" multiple="true" label="browse" update="imagePreview" invalidFileMessage="Invalid image" invalidSizeMessage="too large size"/>
    <p:outputPanel id="imagePreview">
        <ui:repeat value="#{clientController.listImages}" var="imageId">
            <div style="float:left;margin-right:10px; margin-bottom: 5px;">
                <p:graphicImage value="#{clientController.previewImage}" height="135" width="135" styleClass="images">
                    <f:param name="imageId" value="#{imageId}"/>
                </p:graphicImage>
            </div>
        </ui:repeat>
    </p:outputPanel>
</h:form>

Bean代码：

private Map<UUID, UploadedFile> uploadedFiles = new HashMap<UUID, UploadedFile>();//used for preview
  private List<String> listImages = new ArrayList<String>(); //list of id from map which is UUID
 private List<UploadedFile> clientProfile = new ArrayList<UploadedFile>();


public void uploadListener(FileUploadEvent event) {
    clientProfile.add(event.getFile());
    final UUID uuid = UUID.randomUUID();
    uploadedFiles.put(uuid, event.getFile());
    listImages.add(uuid.toString());
    System.out.println(listImages.size());
    System.out.println(clientProfile.size());
  }

  public List<String> getListImages() {
    return listImages;
  }

  public StreamedContent getPreviewImage() {
    FacesContext context = FacesContext.getCurrentInstance();
    if (context.getCurrentPhaseId() == PhaseId.RENDER_RESPONSE) {
      return new DefaultStreamedContent();
    } else {
      StreamedContent image = null;
      String imageId = JsfUtil.getRequestParameter("imageId");
      System.out.println(imageId);
      if (imageId != null) {
        UUID imageIndex = UUID.fromString(imageId);
        return new DefaultStreamedContent(new ByteArrayInputStream(uploadedFiles.get(imageIndex).getContents()));
      }
    }
    return null;

  }