Java tutorial
/* * Licensed to the Apache Software Foundation (ASF) under one or more * contributor license agreements. See the NOTICE file distributed with * this work for additional information regarding copyright ownership. * The ASF licenses this file to You under the Apache License, Version 2.0 * (the "License"); you may not use this file except in compliance with * the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package org.apache.lucene.search; import java.io.IOException; import java.util.Objects; import java.util.Set; import org.apache.lucene.index.IndexReaderContext; import org.apache.lucene.index.LeafReader; import org.apache.lucene.index.LeafReaderContext; import org.apache.lucene.index.PostingsEnum; import org.apache.lucene.index.ReaderUtil; import org.apache.lucene.index.Term; import org.apache.lucene.index.TermState; import org.apache.lucene.index.TermStates; import org.apache.lucene.index.TermsEnum; import org.apache.lucene.search.similarities.Similarity; /** * A Query that matches documents containing a term. This may be combined with * other terms with a {@link BooleanQuery}. */ public class TermQuery extends Query { private final Term term; private final TermStates perReaderTermState; final class TermWeight extends Weight { private final Similarity similarity; private final Similarity.SimScorer simScorer; private final TermStates termStates; private final ScoreMode scoreMode; public TermWeight(IndexSearcher searcher, ScoreMode scoreMode, float boost, TermStates termStates) throws IOException { super(TermQuery.this); if (scoreMode.needsScores() && termStates == null) { throw new IllegalStateException("termStates are required when scores are needed"); } this.scoreMode = scoreMode; this.termStates = termStates; this.similarity = searcher.getSimilarity(); final CollectionStatistics collectionStats; final TermStatistics termStats; if (scoreMode.needsScores()) { collectionStats = searcher.collectionStatistics(term.field()); termStats = termStates.docFreq() > 0 ? searcher.termStatistics(term, termStates.docFreq(), termStates.totalTermFreq()) : null; } else { // we do not need the actual stats, use fake stats with docFreq=maxDoc=ttf=1 collectionStats = new CollectionStatistics(term.field(), 1, 1, 1, 1); termStats = new TermStatistics(term.bytes(), 1, 1); } if (termStats == null) { this.simScorer = null; // term doesn't exist in any segment, we won't use similarity at all } else { this.simScorer = similarity.scorer(boost, collectionStats, termStats); } } @Override public void extractTerms(Set<Term> terms) { terms.add(getTerm()); } @Override public Matches matches(LeafReaderContext context, int doc) throws IOException { TermsEnum te = getTermsEnum(context); if (te == null) { return null; } if (context.reader().terms(term.field()).hasPositions() == false) { return super.matches(context, doc); } return MatchesUtils.forField(term.field(), () -> { PostingsEnum pe = te.postings(null, PostingsEnum.OFFSETS); if (pe.advance(doc) != doc) { return null; } return new TermMatchesIterator(getQuery(), pe); }); } @Override public String toString() { return "weight(" + TermQuery.this + ")"; } @Override public Scorer scorer(LeafReaderContext context) throws IOException { assert termStates == null || termStates.wasBuiltFor(ReaderUtil.getTopLevelContext( context)) : "The top-reader used to create Weight is not the same as the current reader's top-reader (" + ReaderUtil.getTopLevelContext(context); ; final TermsEnum termsEnum = getTermsEnum(context); if (termsEnum == null) { return null; } LeafSimScorer scorer = new LeafSimScorer(simScorer, context.reader(), term.field(), scoreMode.needsScores()); if (scoreMode == ScoreMode.TOP_SCORES) { return new TermScorer(this, termsEnum.impacts(PostingsEnum.FREQS), scorer); } else { return new TermScorer(this, termsEnum.postings(null, scoreMode.needsScores() ? PostingsEnum.FREQS : PostingsEnum.NONE), scorer); } } @Override public boolean isCacheable(LeafReaderContext ctx) { return true; } /** * Returns a {@link TermsEnum} positioned at this weights Term or null if * the term does not exist in the given context */ private TermsEnum getTermsEnum(LeafReaderContext context) throws IOException { assert termStates != null; assert termStates.wasBuiltFor(ReaderUtil.getTopLevelContext( context)) : "The top-reader used to create Weight is not the same as the current reader's top-reader (" + ReaderUtil.getTopLevelContext(context); final TermState state = termStates.get(context); if (state == null) { // term is not present in that reader assert termNotInReader(context.reader(), term) : "no termstate found but term exists in reader term=" + term; return null; } final TermsEnum termsEnum = context.reader().terms(term.field()).iterator(); termsEnum.seekExact(term.bytes(), state); return termsEnum; } private boolean termNotInReader(LeafReader reader, Term term) throws IOException { // only called from assert // System.out.println("TQ.termNotInReader reader=" + reader + " term=" + // field + ":" + bytes.utf8ToString()); return reader.docFreq(term) == 0; } @Override public Explanation explain(LeafReaderContext context, int doc) throws IOException { TermScorer scorer = (TermScorer) scorer(context); if (scorer != null) { int newDoc = scorer.iterator().advance(doc); if (newDoc == doc) { float freq = scorer.freq(); LeafSimScorer docScorer = new LeafSimScorer(simScorer, context.reader(), term.field(), true); Explanation freqExplanation = Explanation.match(freq, "freq, occurrences of term within document"); Explanation scoreExplanation = docScorer.explain(doc, freqExplanation); return Explanation.match(scoreExplanation.getValue(), "weight(" + getQuery() + " in " + doc + ") [" + similarity.getClass().getSimpleName() + "], result of:", scoreExplanation); } } return Explanation.noMatch("no matching term"); } } /** Constructs a query for the term <code>t</code>. */ public TermQuery(Term t) { term = Objects.requireNonNull(t); perReaderTermState = null; } /** * Expert: constructs a TermQuery that will use the provided docFreq instead * of looking up the docFreq against the searcher. */ public TermQuery(Term t, TermStates states) { assert states != null; term = Objects.requireNonNull(t); perReaderTermState = Objects.requireNonNull(states); } /** Returns the term of this query. */ public Term getTerm() { return term; } @Override public Weight createWeight(IndexSearcher searcher, ScoreMode scoreMode, float boost) throws IOException { final IndexReaderContext context = searcher.getTopReaderContext(); final TermStates termState; if (perReaderTermState == null || perReaderTermState.wasBuiltFor(context) == false) { termState = TermStates.build(context, term, scoreMode.needsScores()); } else { // PRTS was pre-build for this IS termState = this.perReaderTermState; } return new TermWeight(searcher, scoreMode, boost, termState); } @Override public void visit(QueryVisitor visitor) { if (visitor.acceptField(term.field())) { visitor.consumeTerms(this, term); } } /** Prints a user-readable version of this query. */ @Override public String toString(String field) { StringBuilder buffer = new StringBuilder(); if (!term.field().equals(field)) { buffer.append(term.field()); buffer.append(":"); } buffer.append(term.text()); return buffer.toString(); } /** Returns the {@link TermStates} passed to the constructor, or null if it was not passed. * * @lucene.experimental */ public TermStates getTermStates() { return perReaderTermState; } /** Returns true iff <code>other</code> is equal to <code>this</code>. */ @Override public boolean equals(Object other) { return sameClassAs(other) && term.equals(((TermQuery) other).term); } @Override public int hashCode() { return classHash() ^ term.hashCode(); } }