Class PerFieldSimilarityWrapper
java.lang.Object
org.apache.lucene.search.similarities.Similarity
org.apache.lucene.search.similarities.PerFieldSimilarityWrapper
Provides the ability to use a different
Similarity
for different fields.
Subclasses should implement get(String)
to return an appropriate
Similarity (for example, using field-specific parameter values) for the field.
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Nested Class Summary
Nested classes/interfaces inherited from class org.apache.lucene.search.similarities.Similarity
Similarity.SimScorer, Similarity.SimWeight
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Constructor Summary
Constructors -
Method Summary
Modifier and TypeMethodDescriptionfinal long
computeNorm
(FieldInvertState state) Computes the normalization value for a field, given the accumulated state of term processing for this field (seeFieldInvertState
).final Similarity.SimWeight
computeWeight
(float queryBoost, CollectionStatistics collectionStats, TermStatistics... termStats) Compute any collection-level weight (e.g.abstract Similarity
Returns aSimilarity
for scoring a field.final Similarity.SimScorer
simScorer
(Similarity.SimWeight weight, AtomicReaderContext context) Creates a newSimilarity.SimScorer
to score matching documents from a segment of the inverted index.Methods inherited from class org.apache.lucene.search.similarities.Similarity
coord, queryNorm
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Constructor Details
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PerFieldSimilarityWrapper
public PerFieldSimilarityWrapper()Sole constructor. (For invocation by subclass constructors, typically implicit.)
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Method Details
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computeNorm
Description copied from class:Similarity
Computes the normalization value for a field, given the accumulated state of term processing for this field (seeFieldInvertState
).Matches in longer fields are less precise, so implementations of this method usually set smaller values when
state.getLength()
is large, and larger values whenstate.getLength()
is small.- Specified by:
computeNorm
in classSimilarity
- Parameters:
state
- current processing state for this field- Returns:
- computed norm value
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computeWeight
public final Similarity.SimWeight computeWeight(float queryBoost, CollectionStatistics collectionStats, TermStatistics... termStats) Description copied from class:Similarity
Compute any collection-level weight (e.g. IDF, average document length, etc) needed for scoring a query.- Specified by:
computeWeight
in classSimilarity
- Parameters:
queryBoost
- the query-time boost.collectionStats
- collection-level statistics, such as the number of tokens in the collection.termStats
- term-level statistics, such as the document frequency of a term across the collection.- Returns:
- SimWeight object with the information this Similarity needs to score a query.
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simScorer
public final Similarity.SimScorer simScorer(Similarity.SimWeight weight, AtomicReaderContext context) throws IOException Description copied from class:Similarity
Creates a newSimilarity.SimScorer
to score matching documents from a segment of the inverted index.- Specified by:
simScorer
in classSimilarity
- Parameters:
weight
- collection information fromSimilarity.computeWeight(float, CollectionStatistics, TermStatistics...)
context
- segment of the inverted index to be scored.- Returns:
- SloppySimScorer for scoring documents across
context
- Throws:
IOException
- if there is a low-level I/O error
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get
Returns aSimilarity
for scoring a field.
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