刮HN首页 - Handeling简单的HTML Dom错误

Question

我正在使用'简单的HTML Dom'来刮HN的头版（news.ycombinator.com），这很好的大部分的时间。

但是，他们每隔一段时间都会推销一个缺乏刮刀正在寻找的元素（即乐谱，用户名和评论数量）的工作/公司。

这当然，打破了阵列，因此我的脚本的输出：

<?php 

// 2012-02-12 Maximilian (Extract news.ycombinator.com's Front Page) 

// Set the header during development 
//header ("content-type: text/xml"); 

// Call the external PHP Simple HTML DOM Parser (http://simplehtmldom.sourceforge.net/manual.htm) 
include('lib/simple_html_dom.php'); 

date_default_timezone_set('Europe/Berlin'); 

// Download 'news.ycombinator.com' content 
//$tmp = file_get_contents('http://news.ycombinator.com'); 
//file_put_contents('get.tmp', $tmp); 

// Retrieve the content 
$html = file_get_html('tc.tmp'); 

// Set the extraction pattern for each item 
$title = $html->find("tr td table tr td.title a"); 
$score = $html->find("tr td.subtext span"); 
$user = $html->find("tr td.subtext a[href^=user]"); 
$link = $html->find("tr td table tr td.title a"); 
$time = $html->find("tr td.subtext"); 
$additionals = $html->find("tr td.subtext a[href^=item?id]"); 

// Construct the feed by looping through the items 
for($i=0;$i<29;$i++) { 

$cr=1; 

// Check if the item points to an external website 
if (!strstr($link[$i]->href,'http')) { 

$url = 'http://news.ycombinator.com/'.$link[$i]->href; 
$description = "Join the discussion on Hacker News."; 


} else { 

$url = $link[$i]->href; 

// Getting content here 

if (empty($abstract)) { 

$description ="Failed to load any relevant content. Please try again later."; 

} else { 

$description = $abstract; 

} 

} 
// Put all the items together 
    $result .= '<item><id>f'.$i.'</id><title>'.htmlspecialchars(trim($title[$i]->plaintext)).'</title><description><![CDATA['.$description.']]></description><pubDate>'.str_replace(' | '.$additionals[$i]->plaintext,'',str_replace($score[$i]->plaintext.' by '.$user[$i]->plaintext.' ','',$time[$i]->plaintext)).'</pubDate><score>'.$score[$i]->plaintext.'</score><user>'.$user[$i]->plaintext.'</user><comments>'.$additionals[$i]->plaintext.'</comments><id>'.substr($additionals[$i]->href,8).'</id><discussion>http://news.ycombinator.com/'.$additionals[$i]->href.'</discussion><link>'.htmlspecialchars($url).'</link></item>'; 
} 

$output = '<rss><channel><id>news.ycombinator.com Frontpage</id><buildDate>'.date('Y-m-d H:i:s').'</buildDate>'.$result.'</channel></rss>'; 

file_put_contents('tc.xml', $output); 


?> 

这里是正确的输出

<item> 
<id>f0</id> 
<title>Show HN: Bootswatch, free swatches for your Bootstrap site</title> 
<description><![CDATA[Easy to Install Simply download the CSS file from the swatch of your choice and replace the one in Bootstrap. No messing around with hex values. Whole New Feel We've all been there with the black bar and blue buttons. See how a splash of color and typography can transform the feel of your site. Modular Changes are contained in just two LESS files, enabling modification and ensuring forward compatibility.]]></description> 
<pubDate>3 hours ago</pubDate> 
<score>196 points</score> 
<user>parkov</user> 
<comments>30 comments</comments> 
<id>3594540</id> 
<discussion>http://news.ycombinator.com/item?id=3594540</discussion> 
<link>http://bootswatch.com</link> 
</item> 
<item> 
<id>f1</id> 
<title>Louis CK inspires Jim Gaffigan to sell comedy special for $5 online</title> 
<description><![CDATA[Dear Internet Friends,Inspired by the brilliant Louis CK, I have decided to debut my all-new hour stand-up special on my website, Jimgaffigan.com.Beginning sometime in April, “Jim Gaffigan: Mr. Universe” will be available exclusively for download for only $5. A dollar from each download will go directly to The Bob Woodruff Foundation; a charity dedicated to serving injured Veterans and their families.I am confident that the low price of my new comedy special and the fact that 20% of each $5 download will be donated to this very noble cause will prevent people from stealing it. Maybe I’m being naïve, but I trust you guys.]]></description> 
<pubDate>57 minutes ago</pubDate> 
<score>25 points</score> 
<user>rkudeshi</user> 
<comments>4 comments</comments> 
<id>3595285</id> 
<discussion>http://news.ycombinator.com/item?id=3595285</discussion> 
<link>http://www.whosay.com/jimgaffigan/content/218011</link> 
</item> 

这里的一个例子是的例子输出不正确。请注意，元素不是空的，因此我似乎无法捕捉到错误，只是跳到下一个项目。一切都会过去的推广后会打破：

<item> 
<id>f14</id> 
<title>Build the next Legos: We're hiring an iOS Developer &amp; Web Developer (YC S11)</title> 
<description><![CDATA[Interested in building the next generation of toys on digital devices such as the iPad? That’s what we’re doing here at Launchpad Toys with apps like Toontastic (Named one of the “Top 10 iPad Apps of 2011” by the New York Times and was recently added to the iTunes Hall of Fame) and an awesom]]><![CDATA[e suite of others we have under development. We’re looking for creative and playful coders that have made games or highly visual apps/sites in the past for our two open development positions. As a kid, you probably played with Legos endlessly and grew up to be a hacker because you still love building things. Sounds like you? Email us at howdy@launchpadtoys.com with a couple links to some projects and code that we can look at along with your resume.]]></description> 
<pubDate>2 hours ago</pubDate> 
<score>14 points</score> 
<user>bproper</user> 
<comments>7 comments</comments> 
<id>3594944</id> 
<discussion>http://news.ycombinator.com/item?id=3594944</discussion> 
<link>http://launchpadtoys.com/blog/2012/02/iosdeveloper-webdeveloper/</link> 
</item> 
<item> 
<id>f15</id> 
<title>SOPA foe Fred Wilson supports a blacklist on pirate sites</title> 
<description><![CDATA[VC Fred Wilson says Google, Bing, Facebook, and Twitter should warn people when they try to log in at known pirate sites: "We don't need legislation." Fred Wilson says: If they try to pass antipiracy legislation, it will once again be 'war.' (Credit: Greg Sandoval/CNET) Fred Wilson, a well-known ven]]><![CDATA[ture capitalist from New York, says he's in favor of creating a blacklist for Web sites found to traffic in pirated films, music, and other intellectual property. The co-founder of Union Square Ventures told a gathering of media executives at the Paley Center for Media yesterday that he believes a good antipiracy measure would be for Google, Twitter, Facebook, and other major sites to issue warnings to people when they try to connect with a known pirate site. Fred Wilson, a co-founder of Union Square Ventures, says 'Our children have been taught to steal.' (Credit: Union Square Ventures) Wilson favors establishing an independent group to create a "black and white list." "The blacklist are those sites we all know are bad news," he told the audience in New York.]]></description> 
<pubDate>14 points by bproper 2 hours ago | 7 comments</pubDate> 
<score>24 points</score> 
<user>andrewcross</user> 
<comments>12 comments</comments> 
<id>3594558</id> 
<discussion>http://news.ycombinator.com/item?id=3594558</discussion> 
<link>http://news.cnet.com/8301-31001_3-57377862-261/post-sopa-influential-tech-investor-favors-blacklisting-pirate-sites/</link> 
</item> 

因此，这里是我的问题：我如何处理这种情况的特定元素缺失的情况下，找到（）不抛出一个错误？我必须从头开始，还是有更好的方法来抓取HN的首页？

对于任何人都好奇，这里是整个XML文件：http://thequeue.org/api/tc.xml

Answer 1

你必须块，以处理这个工作，似乎有一个虚拟隔离元件，可以帮你：

$news = preg_split('/<tr style="height:5px"><\/tr>/',$html->find('tbody',2)->innertext); 

然后用subselectors：

foreach($news as $article){ 
    $article = str_get_html($article) 
    // No upvote arrow found so its not a valid article 
    if(count($article->find('img')) === 0){ 
     continue; 
    } 
} 

而对于其他要素使用相同的选择

Answer 2

我们将感谢Ivan的思想痕迹，我现在将最初被刮掉的HTML分成一个数组，每个节点代表一个帖子。然后，通过循环中的每一篇文章，我将检查是否存在向上投票的箭头图像。如果不是，我不会将其添加到结果中。最后，所有东西都会被缝合在一起，并且赞助的帖子被排除在外。下面的代码：

$array = explode('<tr style="height:5px"></tr>',$html); 
foreach ($array as $post) { 

    if (!strstr($post,'grayarrow.gif')){}else{ 

    $clean .= $post; 

    } 

} 
unset($array); 
$html = str_get_html($clean.'</body></html>');