Foreplay:
- Are you in the dead of night and want to see some pictures that will make you more awake but suffer from lack of resources...
- Do you want to quickly rush to buy train tickets successfully during the peak travel period on holidays...
- Do you want to quickly and accurately locate products with the best reputation and quality when you are shopping online...
What is a crawler:
- 通过编写程序，模拟浏览器上网，然后让其去互联网上抓取数据的过程。
The value of crawlers:
- Practical application
- Employment
Are reptiles legal or illegal?
- Is not prohibited by law
- Risk of illegality
- Good reptiles malicious reptiles
The risks brought by crawlers can be reflected in the following two aspects:
- 爬虫干扰了被访问网站的正常运营
- 爬虫抓取了收到法律保护的特定类型的数据或信息
How to avoid the bad luck of entering the game in the process of using and writing crawlers?
- 时常的优化自己的程序，避免干扰被访问网站的正常运行
- 在使用，传播爬取到的数据时，审查抓取到的内容，如果发现了涉及到用户隐私
商业机密等敏感内容需要及时停止爬取或传播
Classification of crawlers in usage scenarios
- 通用爬虫：
抓取系统重要组成部分。抓取的是一整张页面数据。
- 聚焦爬虫：
是建立在通用爬虫的基础之上。抓取的是页面中特定的局部内容。
- 增量式爬虫：
检测网站中数据更新的情况。只会抓取网站中最新更新出来的数据。
Reptile sword shield
Anti-crawling mechanism
Portal websites can prevent crawlers from crawling website data by formulating corresponding strategies or technical means.
Anti-anti-climbing strategy
Crawler programs can crack the anti-climbing mechanism in the portal website by formulating relevant strategies or technical means, so as to obtain relevant data in the portal website.
robots.txt agreement:
gentleman agreement. It specifies which data in the website can be crawled by crawlers and which data cannot be crawled.
http protocol
- 概念：就是服务器和客户端进行数据交互的一种形式。
Common request header information
-User-Agent: The identity of the request carrier
-Connection: After the request is completed, whether to disconnect or keep the connection
Common response header information
-Content-Type: the type of data the server responds back to the client
https protocol:
-secure hypertext transfer protocol
Encryption method
-symmetric secret key encryption
-asymmetric secret key encryption
-certificate secret key encryption