With the continuous development of the whole Internet and the accumulation of data, the traditional search engine has been unable to meet the demand for data. Web crawler is a very important technology in the field of network data, which makes the data more valuable through the extraction, screening and analysis of network data.
A web crawler, also called a web spider, looks for its prey on the World Wide Web just like a spider. This spider gets us information from the World Wide Web according to the rules that we have predefined for our implementation. Strictly speaking, a simple crawler application mainly consists of five parts: scheduler, URL manager, web page loader and web page parser.
Scheduler: responsible for scheduling work between other parts.
URL manager: through a certain way to prevent repeated, circular capture of urls.
Web page loader: Converts web content into a string by downloading it through web page loader.
Web page parser: the data downloaded from the web page loader is analyzed by the third-party plug-in, and the effective data extraction is completed.
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