Package org.apache.lucene.search
Class TopDocsCollector<T extends ScoreDoc>
java.lang.Object
org.apache.lucene.search.Collector
org.apache.lucene.search.TopDocsCollector<T>
- Direct Known Subclasses:
TopFieldCollector
,TopScoreDocCollector
A base class for all collectors that return a
Extending classes can override any of the methods to provide their own implementation, as well as avoid the use of the priority queue entirely by passing null to
TopDocs
output. This
collector allows easy extension by providing a single constructor which
accepts a PriorityQueue
as well as protected members for that
priority queue and a counter of the number of total hits.Extending classes can override any of the methods to provide their own implementation, as well as avoid the use of the priority queue entirely by passing null to
TopDocsCollector(PriorityQueue)
. In that case
however, you might want to consider overriding all methods, in order to avoid
a NullPointerException.-
Field Summary
FieldsModifier and TypeFieldDescriptionprotected static final TopDocs
This is used in case topDocs() is called with illegal parameters, or there simply aren't (enough) results.protected PriorityQueue<T>
The priority queue which holds the top documents.protected int
The total number of documents that the collector encountered. -
Constructor Summary
Constructors -
Method Summary
Modifier and TypeMethodDescriptionint
The total number of documents that matched this query.protected TopDocs
newTopDocs
(ScoreDoc[] results, int start) Returns aTopDocs
instance containing the given results.protected void
populateResults
(ScoreDoc[] results, int howMany) Populates the results array with the ScoreDoc instances.topDocs()
Returns the top docs that were collected by this collector.topDocs
(int start) Returns the documents in the rage [start ..topDocs
(int start, int howMany) Returns the documents in the rage [start ..protected int
The number of valid PQ entriesMethods inherited from class org.apache.lucene.search.Collector
acceptsDocsOutOfOrder, collect, setNextReader, setScorer
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Field Details
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EMPTY_TOPDOCS
This is used in case topDocs() is called with illegal parameters, or there simply aren't (enough) results. -
pq
The priority queue which holds the top documents. Note that different implementations of PriorityQueue give different meaning to 'top documents'. HitQueue for example aggregates the top scoring documents, while other PQ implementations may hold documents sorted by other criteria. -
totalHits
protected int totalHitsThe total number of documents that the collector encountered.
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Constructor Details
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TopDocsCollector
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Method Details
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populateResults
Populates the results array with the ScoreDoc instances. This can be overridden in case a different ScoreDoc type should be returned. -
newTopDocs
Returns aTopDocs
instance containing the given results. Ifresults
is null it means there are no results to return, either because there were 0 calls to collect() or because the arguments to topDocs were invalid. -
getTotalHits
public int getTotalHits()The total number of documents that matched this query. -
topDocsSize
protected int topDocsSize()The number of valid PQ entries -
topDocs
Returns the top docs that were collected by this collector. -
topDocs
Returns the documents in the rage [start .. pq.size()) that were collected by this collector. Note that if start >= pq.size(), an empty TopDocs is returned.
This method is convenient to call if the application always asks for the last results, starting from the last 'page'.
NOTE: you cannot call this method more than once for each search execution. If you need to call it more than once, passing each time a differentstart
, you should calltopDocs()
and work with the returnedTopDocs
object, which will contain all the results this search execution collected. -
topDocs
Returns the documents in the rage [start .. start+howMany) that were collected by this collector. Note that if start >= pq.size(), an empty TopDocs is returned, and if pq.size() - start < howMany, then only the available documents in [start .. pq.size()) are returned.
This method is useful to call in case pagination of search results is allowed by the search application, as well as it attempts to optimize the memory used by allocating only as much as requested by howMany.
NOTE: you cannot call this method more than once for each search execution. If you need to call it more than once, passing each time a different range, you should calltopDocs()
and work with the returnedTopDocs
object, which will contain all the results this search execution collected.
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