Home Backend Development PHP Tutorial How to implement web crawler in PHP?

How to implement web crawler in PHP?

May 12, 2023 am 08:18 AM
php accomplish web crawler

With the continuous development of Web technology, Web crawlers have also become an important topic in the Internet era. A web crawler is a program that obtains web page information. It can automatically crawl and parse specified web page content, and then extract information from it and store it in a database. As a commonly used data collection method, Web crawlers have a wide range of applications and can be used in many fields such as data mining, search engines, business analysis, and public opinion monitoring.

In this article, we will learn how to implement a web crawler in PHP. Before that, we need to understand some necessary basic knowledge.

1. What is a web crawler

A web crawler is an automated program that can obtain information from web pages according to certain rules. Web crawler mainly consists of three modules: data collection module, data analysis module and storage module. Among them, the data acquisition module is responsible for obtaining page data from the Web; the data analysis module is responsible for parsing and extracting page data; and the storage module is responsible for storing the extracted data into the database. Under normal circumstances, web crawlers will follow certain crawling strategies, such as depth-first strategy, breadth-first strategy, etc., to achieve the optimal crawling effect.

2. Crawler implementation in PHP

In PHP, we can use curl and simple_html_dom to implement the crawler function. Curl is an open source cross-platform command line tool that can handle various protocols such as HTTP, FTP, SMTP, etc. simple_html_dom is an open source HTML DOM parsing library that can easily extract information from HTML documents. We can combine curl and simple_html_dom to implement a basic PHP crawler.

The following is a simple PHP crawler implementation process:

1. Obtain the content of the target website

In PHP, we can use the curl library to obtain the HTML content of the target website . The specific implementation method is as follows:

$ch = curl_init();//初始化curl
curl_setopt($ch, CURLOPT_URL, $url);//设置请求地址
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);//设置请求参数
$html = curl_exec($ch);//发起请求并获取结果
curl_close($ch);//关闭curl
Copy after login

In the above code, we first use the curl_init() function to initialize a curl handle. Then, we set the request address and request parameters through the curl_setopt() function. Here, we set CURLOPT_RETURNTRANSFER to 1 so that curl returns the result instead of outputting it directly. Next, we use the curl_exec() function to initiate the request and obtain the result, and finally use the curl_close() function to close the curl handle.

2. Parse HTML documents

Next, we need to use the simple_html_dom library to parse and extract the obtained HTML documents. The specific implementation method is as follows:

include_once('simple_html_dom.php');//导入simple_html_dom库
$htmlObj = str_get_html($html);//将HTML字符串转换为HTML对象
foreach($htmlObj->find('a') as $element){//使用选择器提取<a>标签
    echo $element->href;//打印<a>标签的href属性
}
$htmlObj->clear();//清空HTML对象
unset($htmlObj);//销毁HTML对象
Copy after login

In the above code, we first use the include_once() function to import the simple_html_dom library, and then use the str_get_html() function to convert the HTML string into an HTML object. Next, we use selector ‘a’ to extract all tags and use foreach() to loop through each tag. In the loop, we use $element->href to get the href attribute of the current tag and process it. Finally, we use the $htmlObj->clear() method to clear the HTML object, and use the unset() function to destroy the HTML object.

3. Store data

Finally, we need to store the extracted information into the database. The specific implementation method varies depending on the specific situation. Generally, we can use relational databases such as MySQL to store data.

To sum up, we can use curl and the simple_html_dom library to implement a basic PHP crawler. Of course, this is just a simple implementation process. A real crawler program needs to consider many other factors, such as anti-crawler mechanisms, multi-thread processing, information classification, and deduplication. At the same time, you need to pay attention to laws, regulations and ethical standards when using crawlers, abide by website rules, and do not infringe on other people's privacy and intellectual property rights to avoid breaking the law.

Reference:

  1. Detailed explanation of Curl web page crawling method, https://www.cnblogs.com/xuxinstyle/p/13931436.html
  2. Simple_HTML_DOM library Detailed usage instructions, https://www.cnblogs.com/straycats/p/5363855.html

The above is the detailed content of How to implement web crawler in PHP?. For more information, please follow other related articles on the PHP Chinese website!

Statement of this Website
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn

Hot AI Tools

Undresser.AI Undress

Undresser.AI Undress

AI-powered app for creating realistic nude photos

AI Clothes Remover

AI Clothes Remover

Online AI tool for removing clothes from photos.

Undress AI Tool

Undress AI Tool

Undress images for free

Clothoff.io

Clothoff.io

AI clothes remover

AI Hentai Generator

AI Hentai Generator

Generate AI Hentai for free.

Hot Article

R.E.P.O. Energy Crystals Explained and What They Do (Yellow Crystal)
1 months ago By 尊渡假赌尊渡假赌尊渡假赌
R.E.P.O. Best Graphic Settings
1 months ago By 尊渡假赌尊渡假赌尊渡假赌
Will R.E.P.O. Have Crossplay?
1 months ago By 尊渡假赌尊渡假赌尊渡假赌

Hot Tools

Notepad++7.3.1

Notepad++7.3.1

Easy-to-use and free code editor

SublimeText3 Chinese version

SublimeText3 Chinese version

Chinese version, very easy to use

Zend Studio 13.0.1

Zend Studio 13.0.1

Powerful PHP integrated development environment

Dreamweaver CS6

Dreamweaver CS6

Visual web development tools

SublimeText3 Mac version

SublimeText3 Mac version

God-level code editing software (SublimeText3)

PHP 8.4 Installation and Upgrade guide for Ubuntu and Debian PHP 8.4 Installation and Upgrade guide for Ubuntu and Debian Dec 24, 2024 pm 04:42 PM

PHP 8.4 brings several new features, security improvements, and performance improvements with healthy amounts of feature deprecations and removals. This guide explains how to install PHP 8.4 or upgrade to PHP 8.4 on Ubuntu, Debian, or their derivati

How To Set Up Visual Studio Code (VS Code) for PHP Development How To Set Up Visual Studio Code (VS Code) for PHP Development Dec 20, 2024 am 11:31 AM

Visual Studio Code, also known as VS Code, is a free source code editor — or integrated development environment (IDE) — available for all major operating systems. With a large collection of extensions for many programming languages, VS Code can be c

7 PHP Functions I Regret I Didn't Know Before 7 PHP Functions I Regret I Didn't Know Before Nov 13, 2024 am 09:42 AM

If you are an experienced PHP developer, you might have the feeling that you’ve been there and done that already.You have developed a significant number of applications, debugged millions of lines of code, and tweaked a bunch of scripts to achieve op

How do you parse and process HTML/XML in PHP? How do you parse and process HTML/XML in PHP? Feb 07, 2025 am 11:57 AM

This tutorial demonstrates how to efficiently process XML documents using PHP. XML (eXtensible Markup Language) is a versatile text-based markup language designed for both human readability and machine parsing. It's commonly used for data storage an

Explain JSON Web Tokens (JWT) and their use case in PHP APIs. Explain JSON Web Tokens (JWT) and their use case in PHP APIs. Apr 05, 2025 am 12:04 AM

JWT is an open standard based on JSON, used to securely transmit information between parties, mainly for identity authentication and information exchange. 1. JWT consists of three parts: Header, Payload and Signature. 2. The working principle of JWT includes three steps: generating JWT, verifying JWT and parsing Payload. 3. When using JWT for authentication in PHP, JWT can be generated and verified, and user role and permission information can be included in advanced usage. 4. Common errors include signature verification failure, token expiration, and payload oversized. Debugging skills include using debugging tools and logging. 5. Performance optimization and best practices include using appropriate signature algorithms, setting validity periods reasonably,

PHP Program to Count Vowels in a String PHP Program to Count Vowels in a String Feb 07, 2025 pm 12:12 PM

A string is a sequence of characters, including letters, numbers, and symbols. This tutorial will learn how to calculate the number of vowels in a given string in PHP using different methods. The vowels in English are a, e, i, o, u, and they can be uppercase or lowercase. What is a vowel? Vowels are alphabetic characters that represent a specific pronunciation. There are five vowels in English, including uppercase and lowercase: a, e, i, o, u Example 1 Input: String = "Tutorialspoint" Output: 6 explain The vowels in the string "Tutorialspoint" are u, o, i, a, o, i. There are 6 yuan in total

Explain late static binding in PHP (static::). Explain late static binding in PHP (static::). Apr 03, 2025 am 12:04 AM

Static binding (static::) implements late static binding (LSB) in PHP, allowing calling classes to be referenced in static contexts rather than defining classes. 1) The parsing process is performed at runtime, 2) Look up the call class in the inheritance relationship, 3) It may bring performance overhead.

What are PHP magic methods (__construct, __destruct, __call, __get, __set, etc.) and provide use cases? What are PHP magic methods (__construct, __destruct, __call, __get, __set, etc.) and provide use cases? Apr 03, 2025 am 12:03 AM

What are the magic methods of PHP? PHP's magic methods include: 1.\_\_construct, used to initialize objects; 2.\_\_destruct, used to clean up resources; 3.\_\_call, handle non-existent method calls; 4.\_\_get, implement dynamic attribute access; 5.\_\_set, implement dynamic attribute settings. These methods are automatically called in certain situations, improving code flexibility and efficiency.

See all articles