salesforce.com apex:actionPoller example

ActionPollerExample.apxc

public class ActionPollerExample implements Database.Batchable<Integer>, Iterator<Integer>, Iterable<Integer> {
    Integer counter;
    public Id jobId { get; set; }
    public Boolean keepPolling { get; set; }
    
    public ActionPollerExample() {
        counter = 0;
        keepPolling = false;
    }
    public Iterator<Integer> iterator() {
        return this;
    }
    public Integer next() {
        return counter++;
    }
    public Boolean hasNext() {
        return counter<20000;
    }
    public Iterable<Integer> start(Database.BatchableContext context) {
        return this;
    }
    public void execute(Database.BatchableContext context, Integer[] scope) {

    }
    public void finish(Database.BatchableContext context) {
        
    }
    public void actionPollAction() {
        AsyncApexJob job = [SELECT JobItemsProcessed, TotalJobItems, Status FROM AsyncApexJob WHERE Id = :jobId];
        if(job.Status == 'Queued' || job.Status == 'Holding' || job.Status == 'Preparing') {
            ApexPages.addMessage(new ApexPages.Message(ApexPages.Severity.INFO, 'We are in the '+job.Status.toLowerCase()+' status...'));
        } else if(job.Status != 'Completed' && job.Status != 'Aborted') {
            ApexPages.addMessage(new ApexPages.Message(ApexPages.Severity.INFO, 'We are in '+job.Status.toLowerCase()+' status: '+Math.floor(100.0*job.JobItemsProcessed/job.TotalJobItems)+'%...'));
        } else {
            ApexPages.addMessage(new ApexPages.Message(ApexPages.Severity.CONFIRM, 'The job is now '+job.Status.toLowerCase()+'.'));
            keepPolling = false;
        }
    }
    public void startAction() {
        jobId = Database.executeBatch(this);
        ApexPages.addMessage(new ApexPages.Message(ApexPages.Severity.INFO, 'We have started executing the job...'));
        keepPolling = true;
    }
    public void showInitMessage() {
        ApexPages.addMessage(new ApexPages.Message(ApexPages.Severity.INFO, 'We will be starting the batch process in five seconds...'));
    }
}

actionPollerExample.vfp

<apex:page controller="ActionPollerExample" action="{!showInitMessage}">
    <apex:form id="form">
        <apex:pageMessages />
        <apex:actionPoller rendered="{!jobId == null}" action="{!startAction}" interval="5" reRender="form" />
        <apex:actionPoller rendered="{!keepPolling}" action="{!actionPollAction}" interval="5" reRender="form" />
    </apex:form>
</apex:page>