How to create a fast and efficient web crawler with PHP and Selenium

In the vast world of the Internet, there is a huge amount of information that needs to be mined. At this time, web crawlers came into being. However, the way crawlers are written varies widely. Different combinations of languages ​​and tools can have different efficiencies and have different learning costs. This article will introduce how to use PHP and Selenium to create a fast and efficient web crawler.

What is Selenium

Selenium is an automated testing tool that can simulate human operations on web pages. It supports multiple programming languages ​​such as Java, Python, C# and PHP, etc. The current version is Selenium WebDriver. Compared with the previous version, it does not need to use Selenium RC as the middle layer, but communicates directly with the browser, which has greatly improved the speed and stability.

Why choose PHP and Selenium

First of all, PHP is a popular server-side programming language with good readability and scalability. Secondly, Selenium, as an automated testing tool, can drive various browsers, easily simulate human operations on web pages, and capture the final desired data. Finally, since the curl function used in the PHP language may be blocked by the website, Selenium can simulate real browser behavior and is not easily blocked.

Install Selenium

Before installing Selenium, you need to install Composer first. If you have not installed Composer, please refer to the official documentation to install it.

After installing Composer, install Selenium’s PHP interface through Composer:

composer require facebook/webdriver

Write crawler code

First, we need to introduce the Selenium WebDriver client:

require_once 'vendor/autoload.php';
use FacebookWebDriverRemoteRemoteWebDriver;
use FacebookWebDriverWebDriverBy;

Then, we need to instantiate a WebDriver, select the browser to be started and the corresponding driver path:

$driver = RemoteWebDriver::create(
    'http://localhost:9515',
    DesiredCapabilities::chrome()
);

Here we choose to start the Chrome browser, we need to download ChromeDriver in advance and set the driver path:

putenv('webdriver.chrome.driver=/usr/local/bin/chromedriver');

Then, we can open a web page and obtain the data:

$driver->get("https://www.example.com");
$elements = $driver->findElements(WebDriverBy::cssSelector(".example-class"));
foreach ($elements as $element) {
    echo $element->getText() . "
";
}

The code here opens an example.com page, and then finds the class of example-class element and print it out.

How to speed up crawlers

Selenium crawlers are slower than other crawler tools, mainly because each operation requires starting and closing the browser. In order to speed up the crawler, we can cache the WebDriver instance.

$host = 'http://localhost:9515';
$options = new ChromeOptions();
$options->addArguments(['--headless']);
$caps = DesiredCapabilities::chrome();
$caps->setCapability(ChromeOptions::CAPABILITY, $options);
$driver = RemoteWebDriver::create($host, $caps);

function get_web_driver() {
    global $driver;
    $status = true;
    try {
        $driver->getTitle();
    } catch (Exception $e) {
        $status = false;
    }
    if (!$status) {
        $releaseWebDriver = function() use($driver){ $driver->close(); $driver->quit(); };
        register_shutdown_function($releaseWebDriver);
        $options = new ChromeOptions();
        $options->addArguments(['--headless']);
        $caps = DesiredCapabilities::chrome();
        $caps->setCapability(ChromeOptions::CAPABILITY, $options);
        $new_driver = RemoteWebDriver::create(
            'http://localhost:9515',
            $caps
        );
        $driver = $new_driver;
    }
    return $driver;
}

The above code is for the Chrome browser, sets up the Headless mode, and implements the cache of the WebDriver object. It uses the register_shutdown_function() function to log out the WebDriver object operation, thus avoiding frequent startup of the browser. Improved crawler efficiency.

Conclusion

Overall, using PHP combined with Selenium to write a web crawler can quickly and efficiently capture the required data. However, it should be noted that the use of web crawlers still needs to comply with relevant laws and regulations, and must not violate website regulations and must not capture personal information and other data, otherwise you may face unnecessary legal risks.

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