How do crawlers get data from web pages?

To build a web crawler, web page download is an essential step. This is not easy because there are many factors to consider, such as how to make better use of local bandwidth, how to optimize DNS queries, and how to allocate network requests to free up traffic on the server.


1. Complex analysis of HTML pages.


In fact, we can't directly access all HTML web pages. There is also the problem of retrieving javascript-generated content in a dynamic web site using AJAX. In addition, crawler traps often occur on the network, causing numerous requests or crawler crashes.


2. While there are many things you should know when building a Web crawler, most of the time you just want to create a crawler for a specific site.


Not generic programs like Google crawlers. Therefore, it is best to do in-depth research on the target site, select valuable links to track, and avoid the extra cost of redundant or spam urls. In addition, if the right web crawl path can be found, the content of interest to the target site can be captured in a predefined order.


The above mentioned is how to crawl data on the web page, crawler crawl data need to break the IP limit, you can consider using proxy IP.

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