What's the use of web crawler technology?
This article mainly introduces the use of web crawler technology, has a certain reference value, interested friends can refer to, I hope you can learn a lot after reading this article, let the editor take you to understand it.
1. What is a web crawler? what is the function of a web crawler?
With the advent of the era of big data, the position of web crawlers in the Internet will become more and more important. The data in the Internet is huge, how to automatically and efficiently obtain and use the information we are interested in in the Internet is an important problem, and crawler technology is born to solve these problems.
two。 The use of web crawlers!
Web crawlers, also known as web spiders, web ants, web robots, etc., can automatically browse the information in the network, of course, we need to browse the information in accordance with our rules, these rules we call web crawler algorithm.
Search engines can not do without crawlers, such as Baidu search engine crawlers called Baidu spiders (Baiduspider). Baidu spiders will crawl in the vast amount of Internet information every day, crawl high-quality information and collect it. When users retrieve corresponding keywords on Baidu search engine, Baidu will analyze and process the keywords, find out the relevant pages from the included pages, sort them according to certain ranking rules and show the results to users.
In this process, Baidu spiders played a vital role. So, how to cover more high-quality web pages in the Internet? How do you filter these duplicate pages? These are determined by the algorithm of Baidu spider crawler. Using different algorithms, the running efficiency of the crawler will be different, and the crawling results will be different.
In addition to Baidu search engine can not do without crawlers, other search engines can not do without crawlers, they also have their own crawlers. For example, 360's reptile is called 360Spider, Sogou's reptile is called Sogouspider, and Bing's reptile is called Bingbot.
Big data era is also inseparable from crawlers, such as big data analysis or data mining, we can go to some large official sites to download data sources. But these data sources are limited, so how can we obtain more and higher quality data sources? At this time, we can write our own crawler program to obtain data and information from the Internet. So in the future, the status of reptiles will become more and more important.
3. The basic workflow of a web crawler.
(1) first select part of the seed URL
(2) put these URL in the URL queue to be crawled
(3) take out the URL to be crawled from the URL queue to be crawled, parse the DNS, get the IP of the host, download the web page corresponding to the URL and store it in the downloaded web page library, in addition, put the URL into the crawled URL queue.
(4) analyze the other URL in the crawled web page content, and put the URL into the URL queue to be crawled, so as to enter the next loop
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