Create a PHP-based web crawler

With the rapid development of the Internet, the acquisition and utilization of information has become more and more important. Web crawlers, as an automated program, can help us quickly crawl information from the Internet and process it, thus greatly improving the efficiency of information utilization. In this article, I will explain how to create a simple web crawler using PHP.

1. Basic knowledge of web crawlers

Web crawlers are an automated program that can simulate human browsing behavior on web pages and automatically capture relevant information on web pages. Web crawlers have many uses, such as search engine crawling, data mining, price comparison, and content aggregation.

The running process of the Web crawler is roughly as follows:

1. Determine the web page address to be crawled.
2. Make an HTTP request to the target web page and get the response.
3. Extract the required data from the response.
4. Process and store data.

The core of a Web crawler is to parse HTML documents and extract the required information. In PHP, we can use the DOMDocument class or SimpleXMLElement class to parse XML documents, and use regular expressions or string functions to parse HTML documents.

2. Create a PHP-based Web crawler

Below we will use a practical example to illustrate how to create a PHP-based Web crawler that can crawl Douban movie rankings Movie information.

1. Determine the webpage address to be crawled

The target we want to crawl is the Douban movie rankings, the URL is: https://movie.douban.com/ chart.

2. Make an HTTP request to the target web page and get the response

In PHP, we can use the cURL library to send an HTTP request and get the response. cURL is an open source network library that supports multiple protocols, such as HTTP, FTP, SMTP, etc.

The following is an example of using the cURL library to send an HTTP request:

$url = "https://movie.douban.com/chart";
$ch = curl_init() ;
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
$response = curl_exec($ch);
curl_close($ch);

In the above code, we first define the web page address $url to be crawled, and use the curl_init() function to initialize a cURL session. Then, use the curl_setopt() function to set curl options, such as the URL to be requested, whether to return a response, etc. Finally, use the curl_exec() function to send the HTTP request, get the response, and use the curl_close() function to close the cURL session.

3. Extract the required data from the response

After getting the response, we need to extract the required movie information from it. In the Douban movie rankings, each movie has a unique ID, and we can obtain detailed information about each movie based on this ID.

Here is an example of using regular expressions to extract movie IDs:

$pattern = '/ce47a1571fbc4e91103bbda1e91edcf6.?(. ?)/s';
preg_match_all($pattern, $response, $matches);

In the above code, we define a regular expression $pattern to match Movie ID and movie name. Use the preg_match_all() function to match the response and save all matching results in the $matches array.

Next, we can use the movie ID obtained previously to grab the detailed information of each movie. Here, we use the SimpleXMLElement class to parse the XML document and extract movie information. Here is an example to extract movie information:

foreach ($matches[1] as $url) {

$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
$response = curl_exec($ch);
curl_close($ch);
$xml = new SimpleXMLElement($response);
echo "电影名称：" . $xml->xpath('//title')[0] . "

";

echo "导演：" . $xml->xpath('//a[@rel="v:directedBy"]/text()')[0] . "

";

echo "主演：" . implode(", ", $xml->xpath('//a[@rel="v:starring"]/text()')) . "

";

echo "评分：" . $xml->xpath('//strong[@class="ll rating_num"]/text()')[0] . "

";
}

In the above code, we are looping through the ID of each movie and getting the details of each movie using cURL library. Then, use the SimpleXMLElement class to parse the XML document and extract information such as movie name, director, starring role, and rating.

4. Processing and storing data

Finally, we can process and store the extracted movie information. Here, we use the echo statement to output the results to the command line window.

If you want to store data into the database, you can use PDO or mysqli extension to connect to the database and insert the data into the corresponding table.

3. Summary

Web crawler is a commonly used automated program that can help us quickly obtain information from the Internet and perform further processing. In PHP, we can use the cURL library to send HTTP requests, use the DOMDocument class or the SimpleXMLElement class to parse XML documents or regular expressions to match HTML documents, thereby realizing the development of web crawlers. I hope this article will help you understand the basic knowledge of web crawlers and use PHP to create web crawlers.

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