6.1.9. < a4j:poll > available since 3.0.0

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### 6.1.9. < a4j:poll > available since 3.0.0

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#### 6.1.9.1. Description

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.

#### 6.1.9.2. Details of Usage

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.

## Notes:

- The form around the <a4j:poll> component is required.

- To make the <a4j:poll> component send requests periodically when it `limitToList` is set to "true", pass the <a4j:poll> ID to it `reRender` attribute.

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

#### 6.1.9.3. Reference Data

Table of <a4j:poll> attributes.

Table 6.9. Component Identification Parameters

Name | Value
--- | ---
component-type | org.ajax4jsf.Poll
component-family | org.ajax4jsf.components.AjaxPoll
component-class | org.ajax4jsf.component.html.AjaxPoll
renderer-type | org.ajax4jsf.components.AjaxPollRenderer

#### 6.1.9.4. Relevant Resources Links

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

Useful examples and articles:

- "Create a Banner Using Effects and Poll" article at RichFaces Wiki gives an example of how to create an image banner using <rich:effect> and <a4j:poll> components;

- "Create an HTML Banner Using Effects and Poll" article at RichFaces Wiki brings the code of the way of creating an HTML banner banner using <rich:effect> and <a4j:poll> components;

- "RichFaces and Slideshow" thread in the RichFaces users forum contains an information and code on making a Slide Show with the help of the <a4j:poll> component;

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

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