The <a4j:poll> component allows periodical sending of Ajax requests to a server and is used for a page updating according to a specified time interval.

The <a4j:poll> componet is used for periodical polling of server data. In order to use the component it's necessary to set an update interval. The "interval" attribute defines an interval in milliseconds between the previous response and the next request. The total period beetween two requests generated by the <a4j:poll> component is a sum of an "interval" attribute value and server response time. Default value for "interval" attribute is set to "1000" milliseconds (1 second). See an example of definition in the "Creating the component with a Page Tag" section.

The "timeout" attribute defines response waiting time in milliseconds. If a response isn't received during this period a connection is aborted and the next request is sent. Default value for "timeout" attribute isn't set.

The "enabled" attribute defines should the <a4j:poll> send request or not. It's necessary to render the <a4j:poll> to apply the current value of "enabled" attribute. You can use an EL-expression for "enabled" attribute to point to a bean property. An example of usage of mentioned above attributes is placed below:

Example:

...

<a4j:region>

      <h:form>

            <a4j:poll id="poll" interval="1000" enabled="#{userBean.pollEnabled}" reRender="poll,grid"/>

      </h:form>

</a4j:region>

<h:form>

      <h:panelGrid columns="2" width="80%" id="grid">

           <h:panelGrid columns="1">

                <h:outputText value="Polling Inactive" rendered="#{not userBean.pollEnabled}" />

                <h:outputText value="Polling Active" rendered="#{userBean.pollEnabled}" />

                <a4j:commandButton style="width:120px" id="control" value="#{userBean.pollEnabled?'Stop':'Start'} Polling" reRender="poll, grid">

                     <a4j:actionparam name="polling" value="#{!userBean.pollEnabled}" assignTo="#{userBean.pollEnabled}"/>

                </a4j:commandButton>

          </h:panelGrid>

          <h:outputText id="serverDate" style="font-size:16px" value="Server Date: #{userBean.date}"/>

    </h:panelGrid>

</h:form>

...

The example shows how date and time are updated on a page in compliance with data taken from a server. The <a4j:poll> componet sends requests to the server every second. "reRender" attribute of the <a4j:poll> contains poll's own Id. Hence, it is self rendered for applying the current value of "enabled" attribute.

Information about the "process" attribute usage you can find "Decide what to process" guide section.

Table of <a4j:poll> attributes.

Visit the Poll page at RichFaces LiveDemo for examples of the component usage and their sources.

Useful examples and articles:

Manage the RichFaces Users Forum for fresh issues about the component usage.