package org.apache.lucene.search.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);
}
}