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    1   package org.apache.lucene.search.highlight;
    2   /**
    3    * Licensed to the Apache Software Foundation (ASF) under one or more
    4    * contributor license agreements.  See the NOTICE file distributed with
    5    * this work for additional information regarding copyright ownership.
    6    * The ASF licenses this file to You under the Apache License, Version 2.0
    7    * (the "License"); you may not use this file except in compliance with
    8    * the License.  You may obtain a copy of the License at
    9    *
   10    *     http://www.apache.org/licenses/LICENSE-2.0
   11    *
   12    * Unless required by applicable law or agreed to in writing, software
   13    * distributed under the License is distributed on an "AS IS" BASIS,
   14    * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   15    * See the License for the specific language governing permissions and
   16    * limitations under the License.
   17    */
   18   
   19   import java.io.IOException;
   20   import java.util.HashSet;
   21   import java.util.Iterator;
   22   
   23   import org.apache.lucene.index.IndexReader;
   24   import org.apache.lucene.index.Term;
   25   import org.apache.lucene.search.BooleanClause;
   26   import org.apache.lucene.search.BooleanQuery;
   27   import org.apache.lucene.search.FilteredQuery;
   28   import org.apache.lucene.search.Query;
   29   import org.apache.lucene.util.StringHelper;
   30   
   31   /**
   32    * Utility class used to extract the terms used in a query, plus any weights.
   33    * This class will not find terms for MultiTermQuery, TermRangeQuery and PrefixQuery classes
   34    * so the caller must pass a rewritten query (see Query.rewrite) to obtain a list of 
   35    * expanded terms. 
   36    * 
   37    */
   38   public final class QueryTermExtractor
   39   {
   40   
   41   	/**
   42   	 * Extracts all terms texts of a given Query into an array of WeightedTerms
   43   	 *
   44   	 * @param query      Query to extract term texts from
   45   	 * @return an array of the terms used in a query, plus their weights.
   46   	 */
   47   	public static final WeightedTerm[] getTerms(Query query) 
   48   	{
   49   		return getTerms(query,false);
   50   	}
   51   
   52   	/**
   53   	 * Extracts all terms texts of a given Query into an array of WeightedTerms
   54   	 *
   55   	 * @param query      Query to extract term texts from
   56   	 * @param reader used to compute IDF which can be used to a) score selected fragments better 
   57   	 * b) use graded highlights eg changing intensity of font color
   58   	 * @param fieldName the field on which Inverse Document Frequency (IDF) calculations are based
   59   	 * @return an array of the terms used in a query, plus their weights.
   60   	 */
   61   	public static final WeightedTerm[] getIdfWeightedTerms(Query query, IndexReader reader, String fieldName) 
   62   	{
   63   	    WeightedTerm[] terms=getTerms(query,false, fieldName);
   64   	    int totalNumDocs=reader.numDocs();
   65   	    for (int i = 0; i < terms.length; i++)
   66           {
   67   	        try
   68               {
   69                   int docFreq=reader.docFreq(new Term(fieldName,terms[i].term));
   70                   // docFreq counts deletes
   71                   if(totalNumDocs < docFreq) {
   72                     docFreq = totalNumDocs;
   73                   }
   74                   //IDF algorithm taken from DefaultSimilarity class
   75                   float idf=(float)(Math.log((float)totalNumDocs/(double)(docFreq+1)) + 1.0);
   76                   terms[i].weight*=idf;
   77               } 
   78   	        catch (IOException e)
   79               {
   80   	            //ignore 
   81               }
   82           }
   83   		return terms;
   84   	}
   85   
   86   	/**
   87   	 * Extracts all terms texts of a given Query into an array of WeightedTerms
   88   	 *
   89   	 * @param query      Query to extract term texts from
   90   	 * @param prohibited <code>true</code> to extract "prohibited" terms, too
   91   	 * @param fieldName  The fieldName used to filter query terms
   92      * @return an array of the terms used in a query, plus their weights.
   93      */
   94   	public static final WeightedTerm[] getTerms(Query query, boolean prohibited, String fieldName) 
   95   	{
   96   		HashSet<WeightedTerm> terms=new HashSet<WeightedTerm>();
   97   		if(fieldName!=null)
   98   		{
   99   		    fieldName= StringHelper.intern(fieldName);
  100   		}
  101   		getTerms(query,terms,prohibited,fieldName);
  102   		return terms.toArray(new WeightedTerm[0]);
  103   	}
  104   	
  105   	/**
  106   	 * Extracts all terms texts of a given Query into an array of WeightedTerms
  107   	 *
  108   	 * @param query      Query to extract term texts from
  109   	 * @param prohibited <code>true</code> to extract "prohibited" terms, too
  110      * @return an array of the terms used in a query, plus their weights.
  111      */
  112   	public static final WeightedTerm[] getTerms(Query query, boolean prohibited) 
  113   	{
  114   	    return getTerms(query,prohibited,null);
  115   	}	
  116   
  117   	//fieldname MUST be interned prior to this call
  118   	private static final void getTerms(Query query, HashSet<WeightedTerm> terms,boolean prohibited, String fieldName) 
  119   	{
  120          	try
  121          	{
  122       		if (query instanceof BooleanQuery)
  123       			getTermsFromBooleanQuery((BooleanQuery) query, terms, prohibited, fieldName);
  124       		else
  125       			if(query instanceof FilteredQuery)
  126       				getTermsFromFilteredQuery((FilteredQuery)query, terms,prohibited, fieldName);
  127       			else
  128       		{
  129   	       		HashSet<Term> nonWeightedTerms=new HashSet<Term>();
  130   	       		query.extractTerms(nonWeightedTerms);
  131   	       		for (Iterator<Term> iter = nonWeightedTerms.iterator(); iter.hasNext();)
  132   				{
  133   					Term term = iter.next();
  134   				    if((fieldName==null)||(term.field()==fieldName))
  135   					{
  136   						terms.add(new WeightedTerm(query.getBoost(),term.text()));
  137   					}
  138   				}
  139       		}
  140   	      }
  141   	      catch(UnsupportedOperationException ignore)
  142   	      {
  143   	    	  //this is non-fatal for our purposes
  144          	  }		        			        	
  145   	}
  146   
  147   	/**
  148   	 * extractTerms is currently the only query-independent means of introspecting queries but it only reveals
  149   	 * a list of terms for that query - not the boosts each individual term in that query may or may not have.
  150   	 * "Container" queries such as BooleanQuery should be unwrapped to get at the boost info held
  151   	 * in each child element. 
  152   	 * Some discussion around this topic here:
  153   	 * http://www.gossamer-threads.com/lists/lucene/java-dev/34208?search_string=introspection;#34208
  154   	 * Unfortunately there seemed to be limited interest in requiring all Query objects to implement
  155   	 * something common which would allow access to child queries so what follows here are query-specific
  156   	 * implementations for accessing embedded query elements. 
  157   	 */
  158   	private static final void getTermsFromBooleanQuery(BooleanQuery query, HashSet<WeightedTerm> terms, boolean prohibited, String fieldName)
  159   	{
  160   		BooleanClause[] queryClauses = query.getClauses();
  161   		for (int i = 0; i < queryClauses.length; i++)
  162   		{
  163   			if (prohibited || queryClauses[i].getOccur()!=BooleanClause.Occur.MUST_NOT)
  164   				getTerms(queryClauses[i].getQuery(), terms, prohibited, fieldName);
  165   		}
  166   	}	
  167   	private static void getTermsFromFilteredQuery(FilteredQuery query, HashSet<WeightedTerm> terms, boolean prohibited, String fieldName)
  168   	{
  169   		getTerms(query.getQuery(),terms,prohibited,fieldName);		
  170   	}
  171   	
  172   }

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