问题
I have configured Nutch 2.3.1 to crawl some news websites. As websites homepages are going to change after one day that why I want to handle home page in some different way so that for homepage, only main categories are crawled instead of text as text will change after sometime ( I have observed similar things in Google). For rest of pages, its working fine ( crawling text etc.)
回答1:
At the moment Nutch doesn't offer any special treatment for homepages, it is just one more URL to crawl. If you want to do this you'll probably need to customise some portions of Nutch.
If you're collecting a fixed set of URLs (that you usually put in the seed file) you can attach some metadata to these URLs and use a different strategy for these URLs. For instance setting a really high score & short fetch interval (https://github.com/apache/nutch/blob/release-2.3.1/src/java/org/apache/nutch/crawl/InjectorJob.java#L56-L59).
Since the generator job will sort the URLs by score, this should work as long as all other URLs have a score lower than the value that you use for the seed URLs. Keep in mind that this will cause Nutch to crawl this URLs every time that a new cycle starts (since the seed URLs are going to be on the top all the time).
If you discover new homepages during your normal craw cycle, then it is tricky because Nutch doesn't have any way of detecting if a given URL is a homepage or not. For this case you'll need to check if the current URL is a homepage, if it is indeed a homepage then, you'll need to modify the score/fetch interval to ensure that this URL ends up in the top ranking URLs.
This workaround could potentially cause some issues: Nutch could end up crawling always only the homepages and not the rest of the URLs, which is not a good case.
You could also write your own generator, this way you have more control and don't rely only on the score, fetch interval alone.
Full disclosure: Although I've used a similar approach in the past we ended up changing this system to use StormCrawler (we were building a news search engine) so we needed more control over when the pages were being fetched (the batch nature of Nutch it is not a great fit for this use case), and some other business cases that needed a more NRT approach.
来源：https://stackoverflow.com/questions/49229907/apache-nutch-2-3-1-website-home-page-handling