Java tutorial
package edu.mit.ll.vizlinc.highlight; /** * 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. */ import java.io.IOException; import java.util.HashSet; import java.util.Iterator; import org.apache.lucene.index.IndexReader; import org.apache.lucene.index.Term; import org.apache.lucene.search.BooleanClause; import org.apache.lucene.search.BooleanQuery; import org.apache.lucene.search.FilteredQuery; import org.apache.lucene.search.Query; import org.apache.lucene.util.StringHelper; /** * Utility class used to extract the terms used in a query, plus any weights. * This class will not find terms for MultiTermQuery, TermRangeQuery and PrefixQuery classes * so the caller must pass a rewritten query (see Query.rewrite) to obtain a list of * expanded terms. * */ public final class QueryTermExtractor { /** * Extracts all terms texts of a given Query into an array of WeightedTerms * * @param query Query to extract term texts from * @return an array of the terms used in a query, plus their weights. */ public static final WeightedTerm[] getTerms(Query query) { return getTerms(query, false); } /** * Extracts all terms texts of a given Query into an array of WeightedTerms * * @param query Query to extract term texts from * @param reader used to compute IDF which can be used to a) score selected fragments better * b) use graded highlights eg changing intensity of font color * @param fieldName the field on which Inverse Document Frequency (IDF) calculations are based * @return an array of the terms used in a query, plus their weights. */ public static final WeightedTerm[] getIdfWeightedTerms(Query query, IndexReader reader, String fieldName) { WeightedTerm[] terms = getTerms(query, false, fieldName); int totalNumDocs = reader.numDocs(); for (int i = 0; i < terms.length; i++) { try { int docFreq = reader.docFreq(new Term(fieldName, terms[i].term)); // docFreq counts deletes if (totalNumDocs < docFreq) { docFreq = totalNumDocs; } //IDF algorithm taken from DefaultSimilarity class float idf = (float) (Math.log((float) totalNumDocs / (double) (docFreq + 1)) + 1.0); terms[i].weight *= idf; } catch (IOException e) { //ignore } } return terms; } /** * Extracts all terms texts of a given Query into an array of WeightedTerms * * @param query Query to extract term texts from * @param prohibited <code>true</code> to extract "prohibited" terms, too * @param fieldName The fieldName used to filter query terms * @return an array of the terms used in a query, plus their weights. */ public static final WeightedTerm[] getTerms(Query query, boolean prohibited, String fieldName) { HashSet<WeightedTerm> terms = new HashSet<WeightedTerm>(); if (fieldName != null) { fieldName = StringHelper.intern(fieldName); } getTerms(query, terms, prohibited, fieldName); return terms.toArray(new WeightedTerm[0]); } /** * Extracts all terms texts of a given Query into an array of WeightedTerms * * @param query Query to extract term texts from * @param prohibited <code>true</code> to extract "prohibited" terms, too * @return an array of the terms used in a query, plus their weights. */ public static final WeightedTerm[] getTerms(Query query, boolean prohibited) { return getTerms(query, prohibited, null); } //fieldname MUST be interned prior to this call private static final void getTerms(Query query, HashSet<WeightedTerm> terms, boolean prohibited, String fieldName) { try { if (query instanceof BooleanQuery) getTermsFromBooleanQuery((BooleanQuery) query, terms, prohibited, fieldName); else if (query instanceof FilteredQuery) getTermsFromFilteredQuery((FilteredQuery) query, terms, prohibited, fieldName); else { HashSet<Term> nonWeightedTerms = new HashSet<Term>(); query.extractTerms(nonWeightedTerms); for (Iterator<Term> iter = nonWeightedTerms.iterator(); iter.hasNext();) { Term term = iter.next(); if ((fieldName == null) || (term.field() == fieldName)) { terms.add(new WeightedTerm(query.getBoost(), term.text())); } } } } catch (UnsupportedOperationException ignore) { //this is non-fatal for our purposes } } /** * extractTerms is currently the only query-independent means of introspecting queries but it only reveals * a list of terms for that query - not the boosts each individual term in that query may or may not have. * "Container" queries such as BooleanQuery should be unwrapped to get at the boost info held * in each child element. * Some discussion around this topic here: * http://www.gossamer-threads.com/lists/lucene/java-dev/34208?search_string=introspection;#34208 * Unfortunately there seemed to be limited interest in requiring all Query objects to implement * something common which would allow access to child queries so what follows here are query-specific * implementations for accessing embedded query elements. */ private static final void getTermsFromBooleanQuery(BooleanQuery query, HashSet<WeightedTerm> terms, boolean prohibited, String fieldName) { BooleanClause[] queryClauses = query.getClauses(); for (int i = 0; i < queryClauses.length; i++) { if (prohibited || queryClauses[i].getOccur() != BooleanClause.Occur.MUST_NOT) getTerms(queryClauses[i].getQuery(), terms, prohibited, fieldName); } } private static void getTermsFromFilteredQuery(FilteredQuery query, HashSet<WeightedTerm> terms, boolean prohibited, String fieldName) { getTerms(query.getQuery(), terms, prohibited, fieldName); } }