Java tutorial
/** * Copyright 2014 National University of Ireland, Galway. * * This file is part of the SIREn project. Project and contact information: * * https://github.com/rdelbru/SIREn * * Licensed 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.sindice.siren.search.node; import java.io.IOException; import org.apache.lucene.index.IndexReader; import org.apache.lucene.index.Term; import org.apache.lucene.index.TermContext; import org.apache.lucene.index.TermState; import org.apache.lucene.index.TermsEnum; import org.apache.lucene.search.BooleanQuery; import org.apache.lucene.search.BoostAttribute; import org.apache.lucene.search.Query; import org.apache.lucene.search.ScoringRewrite; import org.apache.lucene.util.ArrayUtil; import org.apache.lucene.util.ByteBlockPool; import org.apache.lucene.util.BytesRef; import org.apache.lucene.util.BytesRefHash; import org.apache.lucene.util.BytesRefHash.DirectBytesStartArray; import org.apache.lucene.util.RamUsageEstimator; import org.sindice.siren.search.node.MultiNodeTermQuery.RewriteMethod; import org.sindice.siren.search.node.NodeBooleanClause.Occur; /** * Base rewrite method that translates each term into a query, and keeps * the scores as computed by the query. * * <p> * * Code taken from {@link ScoringRewrite} and adapted for SIREn. */ abstract class NodeScoringRewrite<Q extends Query> extends NodeTermCollectingRewrite<Q> { /** * A rewrite method that first translates each term into * {@link NodeBooleanClause.Occur#SHOULD} clause in a * {@link NodeBooleanQuery}, and keeps the scores as computed by the * query. Note that typically such scores are * meaningless to the user, and require non-trivial CPU * to compute, so it's almost always better to use {@link * MultiNodeTermQuery#CONSTANT_SCORE_AUTO_REWRITE_DEFAULT} instead. * * <p><b>NOTE</b>: This rewrite method will hit {@link * NodeBooleanQuery.TooManyClauses} if the number of terms * exceeds {@link NodeBooleanQuery#getMaxClauseCount}. * * @see #setRewriteMethod **/ public final static NodeScoringRewrite<NodeBooleanQuery> SCORING_BOOLEAN_QUERY_REWRITE = new NodeScoringRewrite<NodeBooleanQuery>() { @Override protected NodeBooleanQuery getTopLevelQuery() { return new NodeBooleanQuery(); } @Override protected void addClause(final NodeBooleanQuery topLevel, final Term term, final int docCount, final float boost, final TermContext states) { final NodeTermQuery tq = new NodeTermQuery(term, states); tq.setBoost(boost); topLevel.add(tq, Occur.SHOULD); } @Override protected void checkMaxClauseCount(final int count) { if (count > BooleanQuery.getMaxClauseCount()) throw new BooleanQuery.TooManyClauses(); } }; /** * Like {@link #SCORING_BOOLEAN_QUERY_REWRITE} except * scores are not computed. Instead, each matching * document receives a constant score equal to the * query's boost. * * <p><b>NOTE</b>: This rewrite method will hit {@link * NodeBooleanQuery.TooManyClauses} if the number of terms * exceeds {@link Siren-BooleanQuery#getMaxClauseCount}. * * @see #setRewriteMethod **/ public final static RewriteMethod CONSTANT_SCORE_BOOLEAN_QUERY_REWRITE = new RewriteMethod() { @Override public Query rewrite(final IndexReader reader, final MultiNodeTermQuery query) throws IOException { final NodeBooleanQuery bq = SCORING_BOOLEAN_QUERY_REWRITE.rewrite(reader, query); // TODO: if empty boolean query return NullQuery? if (bq.clauses().isEmpty()) { return bq; } // strip the scores off final Query result = new NodeConstantScoreQuery(bq); result.setBoost(query.getBoost()); return result; } }; /** * This method is called after every new term to check if the number of max clauses * (e.g. in NodeBooleanQuery) is not exceeded. Throws the corresponding * {@link RuntimeException}. */ protected abstract void checkMaxClauseCount(int count) throws IOException; @Override public Q rewrite(final IndexReader reader, final MultiNodeTermQuery query) throws IOException { final Q result = this.getTopLevelQuery(); final ParallelArraysTermCollector col = new ParallelArraysTermCollector(); this.collectTerms(reader, query, col); final int size = col.terms.size(); if (size > 0) { final int sort[] = col.terms.sort(col.termsEnum.getComparator()); final float[] boost = col.array.boost; final TermContext[] termStates = col.array.termState; for (int i = 0; i < size; i++) { final int pos = sort[i]; final Term term = new Term(query.getField(), col.terms.get(pos, new BytesRef())); assert reader.docFreq(term) == termStates[pos].docFreq(); this.addClause(result, term, termStates[pos].docFreq(), query.getBoost() * boost[pos], termStates[pos]); } } return result; } final class ParallelArraysTermCollector extends TermCollector { final TermFreqBoostByteStart array = new TermFreqBoostByteStart(16); final BytesRefHash terms = new BytesRefHash(new ByteBlockPool(new ByteBlockPool.DirectAllocator()), 16, array); TermsEnum termsEnum; private BoostAttribute boostAtt; @Override public void setNextEnum(final TermsEnum termsEnum) throws IOException { this.termsEnum = termsEnum; this.boostAtt = termsEnum.attributes().addAttribute(BoostAttribute.class); } @Override public boolean collect(final BytesRef bytes) throws IOException { final int e = terms.add(bytes); final TermState state = termsEnum.termState(); assert state != null; if (e < 0) { // duplicate term: update docFreq final int pos = (-e) - 1; array.termState[pos].register(state, readerContext.ord, termsEnum.docFreq(), termsEnum.totalTermFreq()); assert array.boost[pos] == boostAtt.getBoost() : "boost should be equal in all segment TermsEnums"; } else { // new entry: we populate the entry initially array.boost[e] = boostAtt.getBoost(); array.termState[e] = new TermContext(topReaderContext, state, readerContext.ord, termsEnum.docFreq(), termsEnum.totalTermFreq()); NodeScoringRewrite.this.checkMaxClauseCount(terms.size()); } return true; } } /** Special implementation of BytesStartArray that keeps parallel arrays for boost and docFreq */ static final class TermFreqBoostByteStart extends DirectBytesStartArray { float[] boost; TermContext[] termState; public TermFreqBoostByteStart(final int initSize) { super(initSize); } @Override public int[] init() { final int[] ord = super.init(); boost = new float[ArrayUtil.oversize(ord.length, RamUsageEstimator.NUM_BYTES_FLOAT)]; termState = new TermContext[ArrayUtil.oversize(ord.length, RamUsageEstimator.NUM_BYTES_OBJECT_REF)]; assert termState.length >= ord.length && boost.length >= ord.length; return ord; } @Override public int[] grow() { final int[] ord = super.grow(); boost = ArrayUtil.grow(boost, ord.length); if (termState.length < ord.length) { final TermContext[] tmpTermState = new TermContext[ArrayUtil.oversize(ord.length, RamUsageEstimator.NUM_BYTES_OBJECT_REF)]; System.arraycopy(termState, 0, tmpTermState, 0, termState.length); termState = tmpTermState; } assert termState.length >= ord.length && boost.length >= ord.length; return ord; } @Override public int[] clear() { boost = null; termState = null; return super.clear(); } } }