PHP MySQL生成多个xml Sitemap索引

Question

我有这个用于生成动态xml站点地图的php类：

类：：

namespace SitemapPHP;
class Sitemap {
    /**
     *
     * @var \XMLWriter
     */
    private $writer;
    private $domain;
    private $path;
    private $filename = 'sitemap';
    private $current_item = 0;
    private $current_sitemap = 0;
    const EXT = '.xml';
    const SCHEMA = 'http://www.sitemaps.org/schemas/sitemap/0.9';
    const DEFAULT_PRIORITY = 0.5;
    const ITEM_PER_SITEMAP = 50000;
    const SEPERATOR = '-';
    const INDEX_SUFFIX = 'index';
    /**
     *
     * @param string $domain
     */
    public function __construct($domain) {
        $this->setDomain($domain);
    }
    /**
     * Sets root path of the website, starting with http:// or https://
     *
     * @param string $domain
     */
    public function setDomain($domain) {
        $this->domain = $domain;
        return $this;
    }
    /**
     * Returns root path of the website
     *
     * @return string
     */
    private function getDomain() {
        return $this->domain;
    }
    /**
     * Returns XMLWriter object instance
     *
     * @return \XMLWriter
     */
    private function getWriter() {
        return $this->writer;
    }
    /**
     * Assigns XMLWriter object instance
     *
     * @param \XMLWriter $writer 
     */
    private function setWriter(\XMLWriter $writer) {
        $this->writer = $writer;
    }
    /**
     * Returns path of sitemaps
     * 
     * @return string
     */
    private function getPath() {
        return $this->path;
    }
    /**
     * Sets paths of sitemaps
     * 
     * @param string $path
     * @return Sitemap
     */
    public function setPath($path) {
        $this->path = $path;
        return $this;
    }
    /**
     * Returns filename of sitemap file
     * 
     * @return string
     */
    private function getFilename() {
        return $this->filename;
    }
    /**
     * Sets filename of sitemap file
     * 
     * @param string $filename
     * @return Sitemap
     */
    public function setFilename($filename) {
        $this->filename = $filename;
        return $this;
    }
    /**
     * Returns current item count
     *
     * @return int
     */
    private function getCurrentItem() {
        return $this->current_item;
    }
    /**
     * Increases item counter
     * 
     */
    private function incCurrentItem() {
        $this->current_item = $this->current_item + 1;
    }
    /**
     * Returns current sitemap file count
     *
     * @return int
     */
    private function getCurrentSitemap() {
        return $this->current_sitemap;
    }
    /**
     * Increases sitemap file count
     * 
     */
    private function incCurrentSitemap() {
        $this->current_sitemap = $this->current_sitemap + 1;
    }
    /**
     * Prepares sitemap XML document
     * 
     */
    private function startSitemap() {
        $this->setWriter(new \XMLWriter());
        if ($this->getCurrentSitemap()) {
            $this->getWriter()->openURI($this->getPath() . $this->getFilename() . self::SEPERATOR . $this->getCurrentSitemap() . self::EXT);
        } else {
            $this->getWriter()->openURI($this->getPath() . $this->getFilename() . self::EXT);
        }
        $this->getWriter()->startDocument('1.0', 'UTF-8');
        $this->getWriter()->setIndent(true);
        $this->getWriter()->startElement('urlset');
        $this->getWriter()->writeAttribute('xmlns', self::SCHEMA);
    }
    /**
     * Adds an item to sitemap
     *
     * @param string $loc URL of the page. This value must be less than 2,048 characters. 
     * @param string|null $priority The priority of this URL relative to other URLs on your site. Valid values range from 0.0 to 1.0.
     * @param string|null $changefreq How frequently the page is likely to change. Valid values are always, hourly, daily, weekly, monthly, yearly and never.
     * @param string|int|null $lastmod The date of last modification of url. Unix timestamp or any English textual datetime description.
     * @return Sitemap
     */
    public function addItem($loc, $priority = self::DEFAULT_PRIORITY, $changefreq = NULL, $lastmod = NULL) {
        if (($this->getCurrentItem() % self::ITEM_PER_SITEMAP) == 0) {
            if ($this->getWriter() instanceof \XMLWriter) {
                $this->endSitemap();
            }
            $this->startSitemap();
            $this->incCurrentSitemap();
        }
        $this->incCurrentItem();
        $this->getWriter()->startElement('url');
        $this->getWriter()->writeElement('loc', $this->getDomain() . $loc);
        if($priority !== null)
            $this->getWriter()->writeElement('priority', $priority);
        if ($changefreq)
            $this->getWriter()->writeElement('changefreq', $changefreq);
        if ($lastmod)
            $this->getWriter()->writeElement('lastmod', $this->getLastModifiedDate($lastmod));
        $this->getWriter()->endElement();
        return $this;
    }
    /**
     * Prepares given date for sitemap
     *
     * @param string $date Unix timestamp or any English textual datetime description
     * @return string Year-Month-Day formatted date.
     */
    private function getLastModifiedDate($date) {
        if (ctype_digit($date)) {
            return date('Y-m-d', $date);
        } else {
            $date = strtotime($date);
            return date('Y-m-d', $date);
        }
    }
    /**
     * Finalizes tags of sitemap XML document.
     *
     */
    private function endSitemap() {
        if (!$this->getWriter()) {
            $this->startSitemap();
        }
        $this->getWriter()->endElement();
        $this->getWriter()->endDocument();
    }
    /**
     * Writes Google sitemap index for generated sitemap files
     *
     * @param string $loc Accessible URL path of sitemaps
     * @param string|int $lastmod The date of last modification of sitemap. Unix timestamp or any English textual datetime description.
     */
    public function createSitemapIndex($loc, $lastmod = 'Today') {
        $this->endSitemap();
        $indexwriter = new \XMLWriter();
        $indexwriter->openURI($this->getPath() . $this->getFilename() . self::SEPERATOR . self::INDEX_SUFFIX . self::EXT);
        $indexwriter->startDocument('1.0', 'UTF-8');
        $indexwriter->setIndent(true);
        $indexwriter->startElement('sitemapindex');
        $indexwriter->writeAttribute('xmlns', self::SCHEMA);
        for ($index = 0; $index < $this->getCurrentSitemap(); $index++) {
            $indexwriter->startElement('sitemap');
            $indexwriter->writeElement('loc', $loc . $this->getFilename() . ($index ? self::SEPERATOR . $index : '') . self::EXT);
            $indexwriter->writeElement('lastmod', $this->getLastModifiedDate($lastmod));
            $indexwriter->endElement();
        }
        $indexwriter->endElement();
        $indexwriter->endDocument();
    }
}

我可以使用：$sitemap->addItem('/', '1.0', 'daily', 'Today');添加项目并使用以下命令添加sitemapindex：$sitemap->createSitemapIndex('http://example.com/sitemap/', 'Today');现在我需要为每个月的存档生成多个站点地图和动态的mysql数据库：

$sql = "SELECT YEAR(FROM_UNIXTIME(timestamp)) AS YEAR, 
                MONTH(FROM_UNIXTIME(timestamp)) AS MONTH 
         FROM ".NEWS_ARTICLES." GROUP BY YEAR, MONTH ORDER BY YEAR DESC, MONTH ";
$newsdata = DataAccess::Fetch($sql);

$currentYear = null;

foreach($newsdata AS $news){            
    $sitemap->setFilename('posts-.'.$news['MONTH'].'-'.$news['YEAR'].'');
    $sitemap->addItem('/post/' . $news['slug'], '0.6', 'weekly', $post['created_at']);
}

但在行动中，我看到一个文件和结果数据。如何为每个月生成一个xml文件并将数据/插入/插入此文件（例如：posts-6-2016.xml posts-7-2016.xml）？！