6.2. Developing a custom Collector

In most applications with full-text search, users are looking for the top documents when sorting by either relevance or field values. The most common usage pattern is such that only these ScoreDocs are visited. In some scenarios, though, users want more control over precisely which documents should be retained during searching.

Lucene allows full customization of what you do with each matching document if you create your own subclass of the abstract Collector base class. For example, perhaps you wish to gather every single document ID that matched the query. Or perhaps with each matched document you’d like to consult its contents or an external resource to collate additional information. We’ll cover both of these examples in this section.