phpSpider practical skills: How to deal with the heterogeneous structure of web content?

phpSpider practical skills: How to deal with the heterogeneous structure of web page content?

In the development process of web crawlers, we often encounter the heterogeneous structure of web page content. Pages with this heterogeneous structure often bring certain challenges to the development of crawlers, because different web pages may use different tags, styles, and layouts, making it complicated to parse web content. This article will introduce some techniques for dealing with heterogeneous structures to help you develop efficient phpSpider.

1. Use multiple parsers

Parsing web page content is an important step in crawler development. Choosing an appropriate parser can improve the adaptability to heterogeneous structures. In PHP, common parsers include regular expressions, XPath and DOM.

1. Regular expression: suitable for simple structures, you can extract the required content by defining pattern matching. But for web pages with complex structures, using regular expressions can become very complex and difficult.

// 使用正则表达式提取网页标题
$html = file_get_contents('http://example.com');
preg_match("/<title>(.*?)</title>/i", $html, $matches);
$title = $matches[1];

2. XPath: Suitable for XML-structured web pages, you can easily locate and extract the required content by using XPath expressions.

// 使用XPath提取网页标题
$dom = new DOMDocument();
$dom->loadHTMLFile('http://example.com');
$xpath = new DOMXPath($dom);
$nodeList = $xpath->query("//title");
$title = $nodeList->item(0)->nodeValue;

3. DOM: Suitable for web pages with any structure, the required content can be extracted by operating the DOM tree.

// 使用DOM提取网页标题
$dom = new DOMDocument();
$dom->loadHTMLFile('http://example.com');
$elements = $dom->getElementsByTagName("title");
$title = $elements->item(0)->nodeValue;

By flexibly using the above three parsers, you can choose the appropriate parsing method according to different web page structures and extract the required content.

2. Processing dynamic content

The content of some web pages is dynamically loaded through Ajax or JavaScript. At this time, a JavaScript parsing engine is required to parse the web content. In PHP, you can use tools such as PhantomJS or Selenium to simulate browser behavior and implement dynamic content processing.

The following is a sample code for using PhantomJS to parse dynamic content:

$command = 'phantomjs --ssl-protocol=any --ignore-ssl-errors=true script.js';
$output = shell_exec($command);
$data = json_decode($output, true);

Among them, script.js is a PhantomJS script file. By executing the script, you can obtain dynamically loaded content. The API provided by PhantomJS can be used in the script to simulate browser operations, obtain web page content and return it to the crawler.

3. Processing verification codes

In order to prevent crawlers, some websites will add a verification code mechanism when logging in or submitting a form. Processing verification codes is one of the difficulties in crawler development. Common verification code types include image verification codes and text verification codes.

For image verification codes, you can use OCR (optical character recognition) technology to identify the characters in the verification code. In PHP, you can use OCR libraries such as Tesseract for verification code recognition. The following is a simple verification code recognition example:

// 使用Tesseract进行验证码识别
$command = 'tesseract image.png output';
exec($command);
$output = file_get_contents('output.txt');
$verificationCode = trim($output);

For text verification codes, artificial intelligence technology can be used to process. Using deep learning methods, a model can be trained to automatically recognize text verification codes.

Summary:

Handling the heterogeneous structure of web content is a major challenge in crawler development, but through techniques such as choosing an appropriate parser, processing dynamic content, and identifying verification codes, it can be improved The adaptability of reptiles. I hope that the phpSpider practical skills introduced in this article will be helpful to you when processing heterogeneous structured web content.

Reference:

1. PHP Manual: https://www.php.net/manual/en/book.dom.php
2. XPath Tutorial: https ://www.w3schools.com/xml/xpath_intro.asp
3. PhantomJS: http://phantomjs.org/
4. Tesseract OCR: https://github.com/tesseract-ocr /tesseract

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