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Lucene example source code file (QueryTermExtractor.java)

This example Lucene source code file (QueryTermExtractor.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Lucene tags/keywords

booleanclause, booleanquery, booleanquery, filteredquery, hashset, hashset, indexreader, io, ioexception, iterator, string, string, term, util, weightedterm, weightedterm

The Lucene QueryTermExtractor.java source code

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 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();
		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 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();
	       		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);		
	}
	
}

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