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JBoss.orgCommunity Documentation

6.21.  < a4j:poll >

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.

Table 6.42. a4j : poll attributes

Attribute NameDescription
actionMethodBinding pointing at the application action to be invoked, if this UIComponent is activated by you, during the Apply Request Values or Invoke Application phase of the request processing lifecycle, depending on the value of the immediate property
actionListenerMethodBinding pointing at method accepting an ActionEvent with return type void
ajaxSingleboolean attribute which provides possibility to limit JSF tree processing(decoding, conversion/validation, value applying) to the component which send the request only
bindingThe attribute takes a value-binding expression for a component property of a backing bean
bypassUpdatesIf "true", after process validations phase it skips updates of model beans on a force render response. It can be used for validating components input
dataSerialized (on default with JSON) data passed on the client by a developer on AJAX request. It's accessible via "data.foo" syntax
enabledEnables/disables polling. Default value is "true".
eventsQueueName of requests queue to avoid send next request before complete other from same event. Can be used to reduce number of requests of frequently events (key press, mouse move etc.)
focusid of element to set focus after request completed on client side
idEvery component may have a unique id that is automatically created if omitted
ignoreDupResponsesAttribute allows to ignore an Ajax Response produced by a request if the newest 'similar' request is in a queue already. ignoreDupResponses="true" does not cancel the request while it is processed on the server, but just allows to avoid unnecessary updates on the client side if the response isn't actual now
immediateTrue means, that the default ActionListener should be executed immediately (i.e. during Apply Request Values phase of the request processing lifecycle), rather than waiting until the Invoke Application phase
intervalInterval (in ms) for call poll requests. Default value is "1000"ms (1 second).
limitToListIf "true", then of all AJAX-rendered on the page components only those will be updated, which ID's are passed to the "reRender" attribute of the describable component. "false"-the default value-means that all components with ajaxRendered="true" will be updated.
onbeforedomupdateThe client side script method to be called before DOM is updated
oncompleteThe client side script method to be called after the request is completed
onsubmitJavaScript code for call before submission of ajax event
processId['s] (in format of call UIComponent.findComponent()) of components, processed at the phases 2-5 in case of AjaxRequest caused by this component. Can be single id, comma-separated list of Id's, or EL Expression with array or Collection
renderedIf "false", this component is not rendered
reRenderId['s] (in format of call UIComponent.findComponent()) of components, rendered in case of AjaxRequest caused by this component. Can be single id, comma-separated list of Id's, or EL Expression with array or Collection
similarityGroupingIdIf there are any component requests with identical IDs then these requests will be grouped.
statusID (in format of call UIComponent.findComponent()) of Request status component
timeoutTimeout (in ms) for request

Table 6.43. Component identification parameters

NameValue
component-typeorg.ajax4jsf.Poll
component-familyorg.ajax4jsf.components.AjaxPoll
component-classorg.ajax4jsf.component.html.AjaxPoll
renderer-typeorg.ajax4jsf.components.AjaxPollRenderer

To create the simplest variant on a page use the following syntax:

Example:


<a4j:poll interval="500" reRender="grid"/>

Example:

import org.ajax4jsf.component.html.AjaxPoll;

...
AjaxPoll myPoll = new AjaxPoll();
...

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 on a page" 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 for <a4j:poll> contains value of its own Id. Hence, it renders itself for applying the current value of "enabled" attribute.

Note:

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

Note:

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.

In RichFaces Wiki article "Creating a Banner Using Effects and Poll" you can get additional information how to create an image banner using <rich:effect> and <a4j:poll> components and also you can figure out how to create an HTML banner in RichFaces Wiki article "Creating an HTML Banner Using Effects and Poll" .

In RichFaces Cookbook article on Slide Show" you can find information how to make a Slide Show with help of the <rich:effect> and <a4j:poll> components.

On RichFaces Live Demo page you can see the example of <a4j:poll> usage and sources for the given example.

The additional information about component usage you can find in RichFaces Users Forum .