Code related to https://github.com/prestaconcept/PrestaSitemapBundle/issues/17#issuecomment-19031466

CollegeRankingListener.php

<?php
namespace Absolvent\AbsolventBundle\EventListener\SitemapListener;

use Absolvent\AbsolventBundle\EventListener\SitemapListener;
use Absolvent\Common\Enum\CollegeCourseType;
use Presta\SitemapBundle\Sitemap\Url\UrlConcrete;

class CollegeRankingListener extends SitemapListener
{
    protected $section = 'college_ranking';
    protected $changefreq = UrlConcrete::CHANGEFREQ_WEEKLY;
    protected $priority = 0.5;
    protected $hasNextPage = true;
    protected $onDemandOnly = true;

    protected $items = [];

    protected function getItems($page)
    {
        // selecting informations from db using $page parameter
        return $this->items;
    }

    protected function getEntry($item)
    {
        $jobSearchUrl = $this->container->get('absolvent.url_generator');

        return [
            'url' => $jobSearchUrl->ranking($item)
        ];
    }

    // [...]

SitemapListener.php

<?php
namespace Absolvent\AbsolventBundle\EventListener;

use Absolvent\Common\EventListener;
use Presta\SitemapBundle\Event\SitemapPopulateEvent;
use Presta\SitemapBundle\Service\SitemapListenerInterface;
use Presta\SitemapBundle\Sitemap\Url\UrlConcrete;
use Symfony\Component\Routing\RouterInterface;

abstract class SitemapListener extends EventListener implements SitemapListenerInterface
{
    protected $section;
    protected $changefreq = UrlConcrete::CHANGEFREQ_WEEKLY;
    protected $priority = 0.5;
    protected $hasNextPage = false;
    protected $onDemandOnly = false;

    protected $generator;

    public function populateSitemap(SitemapPopulateEvent $event)
    {
        $section = $event->getSection();
        $this->generator = $event->getGenerator();

        if ((false === is_null($section) && $section != $this->section) ||
            (null === $section && $this->onDemandOnly)) {
            return;
        }

        echo "Generating $this->section\n";

        gc_enable();
        $page = 0;
        do {
            $items = $this->getItems($page++);

            $jobSearchUrl = $this->container->get('job.search.url');

            foreach ($items as $item) {
                $jobSearchUrl->reset();
                $entry = $this->getEntry($item);
                $this->addUrl($entry['url'],
                    array_key_exists('date', $entry) ? $entry['date'] : null,
                    $this->changefreq,
                    $this->priority,
                    $this->section);
            }
            unset($items);
            gc_collect_cycles();
        } while ($this->hasNextPage);
        gc_disable();
        echo "End Generating $this->section\n";
        echo "-------------\n";
  }

	protected function addUrl($url, $date, $changefreq, $priority, $section)
    {
        $this
        	->generator
        	->addUrl(new UrlConcrete($url, $date, $changefreq, $priority), $section);
    }

    /**
     * {@inheritDoc}
     */
    public static function getSubscribedEvents()
    {
        return [
            SitemapPopulateEvent::onSitemapPopulate => ['populateSitemap', 0],
        ];
    }

    abstract protected function getItems($page);
    abstract protected function getEntry($item);
}

I remember isset is faster that array_key_exists for micro optim @ L43