如何在PHP中实现RSS订阅

<?xml version="1.0" encoding="UTF-8"?>
<rss version="2.0">
    <channel>
        <title>我的博客</title>
        <link>Http://www.example.com</link>
        <description>这是我的博客</description>
        <lastBuildDate><?=date("r")?></lastBuildDate>
  
        <item>
            <title>文章1</title>
            <link>http://www.example.com/articles/1</link>
            <description>这是文章1的描述</description>
            <pubDate><?=date("r")?></pubDate>
        </item>
  
        <item>
            <title>文章2</title>
            <link>http://www.example.com/articles/2</link>
            <description>这是文章2的描述</description>
            <pubDate><?=date("r")?></pubDate>
        </item>
  
        <!--更多文章-->
  
    </channel>
</rss>

<?php
header("Content-Type: application/rss+xml; charset=utf-8");
echo file_get_contents("rss.xml");
?>

require_once('simplepie.inc');
 
$feed = new SimplePie();
$feed->set_feed_url('http://www.example.com/rss.php');
$feed->init();
$feed->handle_content_type();
 
foreach ($feed->get_items() as $item) {
    echo $item->get_title();
    echo $item->get_permalink();
}

require_once('FeedWriter.php');
 
$feed = new FeedWriter(RSS2);
$feed->setTitle('我的博客');
$feed->setLink('http://www.example.com');
$feed->setDescription('这是我的博客');
$feed->setChannelElements(array('language'=>'zh-cn'));
  
$item = $feed->createNewItem();
$item->setTitle('文章1');
$item->setLink('http://www.example.com/articles/1');
$item->setDescription('这是文章1的描述');
$item->setDate(time());
$feed->addItem($item);
  
$item = $feed->createNewItem();
$item->setTitle('文章2');
$item->setLink('http://www.example.com/articles/2');
$item->setDescription('这是文章2的描述');
$item->setDate(time());
$feed->addItem($item);
  
$feed->generateFeed();