ZK Developer's Reference/Server Push/Configuration

ZK have two implementations: PollingServerPush and CometServerPush. As their name suggest, they implement the Client-Polling and Comet (aka., long-polling) server pushes.

The default implementation depends on which ZK edition you use. If ZK CE and PE, PollingServerPush will be used. If ZK EE, CometServerPush will be used. You configure ZK to use the one you prefer, even to use a custom server push.

Choose an Implementation

Client-polling is based on a timer that peeks the server continuously to see if any data to be pushed to the client, while Comet establishes a permanent connection for instant push. Client-polling will introduce more traffic due to the continuous peeks, but Comet will consume the network connections that a server allows.

Page-level Configuration

You could configure a particular ZK page to use a particular implementation by use of DesktopCtrl.enableServerPush(ServerPush). For example,

((DesktopCtrl)desktop).enableServerPush(
    new org.zkoss.zk.ui.impl.PollingServerPush(2000,5000,-1));

Application-level Configuration

If you would like to change the default server push for the whole application, you could use the the server-push-class element as follows.

<device-config>
    <device-type>ajax</device-type>
    <server-push-class>org.zkoss.zkex.ui.impl.PollingServerPush</server-push-class>
</device-config>

where you could specify any implementation that implements ServerPush.

Customize Client-Polling

PollingServerPush uses a timer to peek if the server has any data to push back. The period between two peeks is determined by a few factors.

• PollingServerPush.delay.min

  The minimal delay to send the second polling request (unit: milliseconds). Default: 1000.

• PollingServerPush.delay.max

  The maximal delay to send the second polling request (unit: milliseconds). Default: 15000.

• PollingServerPush.delay.factor

  The delay factor. The real delay is the processing time multiplies the delay factor. For example, if the last request took 1 second to process, then the client polling will be delayed for 1 x factor seconds. Default: 5.

  The larger the factor is, the longer delay it tends to be.

It could be configured in WEB-INF/xml by use of the preference element as follows.

<preference>
	<name>PollingServerPush.delay.min</name>
	<value>3000</value>
</preference>
<preference>
	<name>PollingServerPush.delay.max</name>
	<value>10000</value>
</preference>
<preference>
	<name>PollingServerPush.delay.factor</name>
	<value>5</value>
</preference>
<!-- JavaScript code to start the server push; rarely required
<preference>
	<name>PollingServerPush.start</name>
	<value></value>
</preference>
<preference>
	<name>PollingServerPush.stop</name>
	<value></value>
</preference>
-->

In additions, you could specify them in the constructor: PollingServerPush.PollingServerPush(int, int, int). For example,

<source lang="java">
((DesktopCtrl)desktop).enableServerPush(
    new org.zkoss.zk.ui.impl.PollingServerPush(2000,10000,3));

</source>

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