Implementation method of high-performance PHP crawler

With the development of the Internet, the amount of information in web pages is getting larger and deeper, and many people need to quickly extract the information they need from massive amounts of data. At this time, crawlers have become one of the important tools. This article will introduce how to use PHP to write a high-performance crawler to quickly and accurately obtain the required information from the network.

1. Understand the basic principles of crawlers

The basic function of a crawler is to simulate a browser to access web pages and obtain specific information. It can simulate a series of user operations in a web browser, such as sending requests to the server, receiving server responses, and parsing HTML codes. The basic process is as follows:

1. Send a request: The crawler first sends the request specified in the URL. The request can be a GET request or a POST request.
2. Get response: After the server receives the request, it returns the corresponding response. The response contains information content that needs to be crawled.
3. Parse HTML code: After the crawler receives the response, it needs to parse the HTML code in the response and extract the required information.
4. Storage data: The crawler stores the acquired data in local files or databases for subsequent use.

2. Basic process of crawler implementation

The basic process of implementing crawler is as follows:

1. Use cURL or file_get_contents function to send a request and obtain the server response.
2. Call DOMDocument or SimpleHTMLDom to parse the HTML code and extract the required data.
3. Store the extracted data in a local file or database.

3. How to improve the performance of the crawler?

1. Set request header information reasonably

When sending a request, we need to set the request header information, as follows:

$header = array(
  'Referer:xxxx',
  'User_Agent:Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1)'
);

Among them, Referer is The source of the request, and User_Agent is the type of simulated browser. Some websites will restrict request header information, so we need to set it according to the specific conditions of the website.

2. Reasonably set the number of concurrency

The number of concurrency refers to the number of requests processed at the same time. Setting the crawler concurrency number can increase the crawling speed, but setting it too high will put too much pressure on the server and may be restricted by the anti-crawling mechanism. Generally speaking, it is recommended that the number of concurrent crawlers should not exceed 10.

3. Use caching technology

Cache technology can reduce repeated requests and improve performance. The crawler can store the response results of the request in a local file or database. Each time it makes a request, it first reads it from the cache. If there is data, it directly returns the data in the cache, otherwise it gets it from the server.

4. Use a proxy server

Visiting the same website multiple times may result in your IP being blocked and unable to crawl data. This restriction can be bypassed using a proxy server. There are two types of proxy servers: paid and free. However, the stability and reliability of free proxies are not high, so you need to be careful when using them.

5. Focus on code optimization and encapsulation

Writing efficient and reusable code can improve crawler performance. Some commonly used functions can be encapsulated to facilitate code use and management, such as function encapsulation for extracting HTML code.

4. Conclusion

This article introduces the use of PHP to write high-performance crawlers, focusing on how to send requests, parse HTML code and improve performance. By properly setting the request header information, the number of concurrency, using caching technology, proxy servers, and optimizing code and encapsulation functions, the performance of the crawler can be improved to obtain the required data accurately and quickly. However, it should be noted that the use of crawlers needs to comply with network ethics and avoid affecting the normal operation of the website.

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