title: Update the image in gwt CellList
body: <p>I am storing image in Google App Engine using Blob. When i add new data in CellList using ListDataProvider's add() method its getting render perfect. </p>
  
  <p>Below is the extended version of AbstractCell:</p>
  
  <pre><code>@Override
  public void render(com.google.gwt.cell.client.Cell.Context context,
          AppsBean value, SafeHtmlBuilder sb) {
      String url=GWT.getModuleBaseURL()+"fetchIcon?appId="+value.getId()+"&amp;requestType=icon";
      sb.appendHtmlConstant("&lt;Table&gt;");
      sb.appendHtmlConstant("&lt;tr&gt;&lt;td rowspan='3'&gt;");
      sb.appendHtmlConstant("&lt;img src='"+url+"' style='width : 75px ;height: 75px;' /&gt;");
      sb.appendHtmlConstant("&lt;/td&gt;&lt;td&gt;");
      sb.appendEscaped(value.getAppName());
      sb.appendHtmlConstant("&lt;/td&gt;&lt;/tr&gt;&lt;tr&gt;&lt;td&gt;");
      sb.appendEscaped(value.getAppLink());
      sb.appendHtmlConstant("&lt;/td&gt;&lt;/tr&gt;&lt;tr&gt;&lt;td&gt;");
      sb.appendEscaped(value.getAppDesc());
      sb.appendHtmlConstant("&lt;/td&gt;&lt;/tr&gt;");
      sb.appendHtmlConstant("&lt;/Table&gt;");
  }
  </code></pre>
  
  <p>Servlet Code:</p>
  
  <pre><code>        String appId = get(request, "appId");
      String requestType = get(request, "requestType");
      log.info("Your request for apps icon: " + appId + ", requestType: " + requestType);
      if (requestType.equalsIgnoreCase("icon")) {
          Apps icon = appsServiceImpl.getApp(Long.valueOf(appId));
          log.info("We got apps for you: " + icon);
          if(icon != null){
              log.info("We got store logo for you: " + icon.getIcon());
              response.getOutputStream().write(icon.getIcon());
          }
      }
  </code></pre>
  
  <p>Now when i am updating the image in Blob i want same to be reflected in CellList's Cell. For updating of cell i am using ListDataProvider's set() method. </p>
  
  <p>Using set() method, the Text data in Cell getting updated perfect but the image is not getting updated. The url also getting generated perfectly but is not again generating the call to the Servlet once the cell got rendered.</p>
  
  <p>Can anyone what should i do so that  will again generate the call to Servlet?</p>