Different websites employ diverse strategies regarding access for web crawlers, influencing how effectively these crawlers can gather public data. Generally, these strategies can be categorized into three types:

 

1.Denial of Access or Delayed Page Returns

One common strategy is to deny access or delay page returns after requests are made. In such cases, websites may return a 404 error page, indicating the inability to provide the requested information, or they may simply not respond for an extended period. This makes it challenging for crawlers to efficiently collect public data.

2.Return of Non-Target Pages

Apart from denying access outright, some websites return non-target pages. This means that the content returned does not match the intended target page. This can mislead crawlers and hinder their ability to collect public data effectively. For instance, certain travel websites may display prices on ticket pages that differ from the actual prices, complicating the task of accurate data retrieval.

3.Increased Access Difficulty

Certain websites introduce measures to increase the difficulty of access, aiming to prevent crawler activity. This may involve requiring users to log in and pass through captcha verification. Such measures can disrupt crawler operations since they are unable to simulate user login and captcha entry processes.

Conclusion

These scenarios are not uncommon in the field of web crawling. Crawlers must adopt different strategies based on the specific circumstances to navigate the access restrictions imposed by different websites, thereby enabling the smooth collection of public data.

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