Howto add a category metadata to your index and be able to search for it. For this, you need to write an indexing filter and a query filter.
Indexing your custom metadata
For the indexing filter, copy the index-more plugin, and change names, dirs, and build files appropriately. The main thing to change is the filter method:
public Document filter(Document doc, Parse parse, FetcherOutput fo)
In it, you can add your own fields. To add a new category with value "puppies", it will look something like this:
doc.add(new Field("category", "puppies", false, true, false));
See the Document.add API for more info on the booleans.
That's pretty much it for indexing.
Searching your metadata
To search for this, you need to create a query filter. Copy the query-site plugin. Again change file names, directories, and build files as needed. The main java file is very simple, just change the string in the line with "super". Instead of:
You would have
Make sure that you put your new index-category and query-category plugins in your nutch-default.xml file. Don't forget to check that it's in your WEB-INF/classess directory too.