The p:poll component in the following code snippet invokes the showMessage() listener method every 10 seconds and updates a feed reader and a growl. The listener method generates the current time. Furthermore, we will define a widget variable in order to stop or start polling using the client-side API. This occurs via command buttons. Take a look at the code for this discussion:

<p:growl id="growl"/>

<p:poll id="poll" listener="#{pollingBean.showMessage}"
  update="sportFeed growl"
  interval="10" widgetVar="pollWidget"/>

<p:commandButton type="button" value="Stop Polling"
  style="margin:15px 5px 15px 0;"
  onclick="PF('pollWidget').stop();"/>
<p:commandButton type="button" value="Start Polling"
  style="margin:15px 0 15px 0;"
  onclick="PF('pollWidget').start();"/>

<h:panelGroup id="sportFeed" layout="block">
  <p:feedReader value="http://rss.news.yahoo.com/rss/sports"
    var="feed" size="10">
    <h:outputText value="#{feed.title}"
      style="font-weight: bold"/>
    <br/>
    <h:outputText value="#{feed.description.value}"
      escape="false"/>
    <p:separator/>
  </p:feedReader>
</h:panelGroup>

The corresponding screenshot illustrates an update with p:poll:

The interval attribute of p:poll defines the time interval, in seconds, at which to execute periodic AJAX requests. The default value is 2 seconds. In the example, we set it to 10. Similar to any other AJAX-ified components, we can specify components to be processed and updated partially with the process and update attributes, respectively. The update attribute in the example contains IDs of p:feedReader and p:growl.

Polling can be stopped and started using the stop() and start()widget methods respectively. We defined two push buttons to execute pollWidget.stop() and pollWidget.start() on a click event.

Poll also supports the autoStart mode. By default, polling starts automatically on page load. To prevent this behavior, set the autoStart attribute to false.

Another useful setting is the timeout attribute, which defines a timeout for AJAX requests in milliseconds. The timeout is not set by default. Setting a valid timeout allows breaking off long-running requests.