Lucene - FuzzyQuery


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FuzzyQuery is used to search documents using fuzzy implementation that is an approximate search based on the edit distance algorithm.

Class Declaration

Following is the declaration for the org.apache.lucene.search.FuzzyQuery class −

public class FuzzyQuery
   extends MultiTermQuery

Fields

Following are the fields for the FuzzyQuery −

  • static int defaultMaxExpansions
  • static float defaultMinSimilarity
  • static int defaultPrefixLength
  • protected Term term

Class Constructors

The following table shows the different class constructors −

S.No. Constructor & Description
1

FuzzyQuery(Term term)

Calls FuzzyQuery(term, 0.5f, 0, Integer.MAX_VALUE)

2

FuzzyQuery(Term term, float minimumSimilarity)

Calls FuzzyQuery(term, minimumSimilarity, 0, Integer.MAX_VALUE)

3

FuzzyQuery(Term term, float minimumSimilarity, int prefixLength)

Calls FuzzyQuery(term, minimumSimilarity, prefixLength, Integer.MAX_VALUE)

4

FuzzyQuery(Term term, float minimumSimilarity, int prefixLength, int maxExpansions)

Create a new FuzzyQuery that will match terms with a similarity of at least minimum Similarity to term

Class Methods

The following table shows the different class methods −

S.No. Method & Description
1

boolean equals(Object obj)

2

protected FilteredTermEnum getEnum(IndexReader reader)

Constructs the enumeration to be used, expanding the pattern term.

3

float getMinSimilarity()

Returns the minimum similarity that is required for this query to match.

4

int getPrefixLength()

Returns the non-fuzzy prefix length.

5

Term getTerm()

Returns the pattern term.

6

int hashCode()

7

String to String(String field)

Prints a query to a string, with field assumed to be the default field and omitted.

Methods Inherited

This class inherits methods from the following classes −

  • org.apache.lucene.search.MultiTermQuery
  • org.apache.lucene.search.Query
  • java.lang.Object

Usage

private void searchUsingFuzzyQuery(String searchQuery)
   throws IOException, ParseException {
   searcher = new Searcher(indexDir);
   long startTime = System.currentTimeMillis();
   
   //create a term to search file name
   Term term = new Term(LuceneConstants.FILE_NAME, searchQuery);
   //create the term query object
   Query query = new FuzzyQuery(term);
   //do the search
   TopDocs hits = searcher.search(query);
   long endTime = System.currentTimeMillis();

   System.out.println(hits.totalHits +
      " documents found. Time :" + (endTime - startTime) + "ms");
   for(ScoreDoc scoreDoc : hits.scoreDocs) {
      Document doc = searcher.getDocument(scoreDoc);
      System.out.print("Score: "+ scoreDoc.score + " ");
      System.out.println("File: "+ doc.get(LuceneConstants.FILE_PATH));
   }
   searcher.close();
}

Example Application

Let us create a test Lucene application to test search using FuzzyQuery.

Step Description
1 Create a project with a name LuceneFirstApplication under a package com.tutorialspoint.lucene as explained in the Lucene - First Application chapter. You can also use the project created in Lucene - First Application chapter as such for this chapter to understand searching process.
2 Create LuceneConstants.java and Searcher.java as explained in the Lucene - First Application chapter. Keep rest of the files unchanged.
3 Create LuceneTester.java as mentioned below.
4 Clean and Build the application to make sure the business logic is working as per the requirements.

LuceneConstants.java

This class is used to provide various constants to be used across the sample application.

package com.tutorialspoint.lucene;

public class LuceneConstants {
   public static final String CONTENTS = "contents";
   public static final String FILE_NAME = "filename";
   public static final String FILE_PATH = "filepath";
   public static final int MAX_SEARCH = 10;
}

Searcher.java

This class is used to read the indexes made on raw data and searches data using the Lucene library.

package com.tutorialspoint.lucene;

import java.io.File;
import java.io.IOException;

import org.apache.lucene.analysis.standard.StandardAnalyzer;
import org.apache.lucene.document.Document;
import org.apache.lucene.index.CorruptIndexException;
import org.apache.lucene.queryParser.ParseException;
import org.apache.lucene.queryParser.QueryParser;
import org.apache.lucene.search.IndexSearcher;
import org.apache.lucene.search.Query;
import org.apache.lucene.search.ScoreDoc;
import org.apache.lucene.search.TopDocs;
import org.apache.lucene.store.Directory;
import org.apache.lucene.store.FSDirectory;
import org.apache.lucene.util.Version;

public class Searcher {
	
   IndexSearcher indexSearcher;
   QueryParser queryParser;
   Query query;

   public Searcher(String indexDirectoryPath) throws IOException {
      Directory indexDirectory = 
         FSDirectory.open(new File(indexDirectoryPath));
      indexSearcher = new IndexSearcher(indexDirectory);
      queryParser = new QueryParser(Version.LUCENE_36,
         LuceneConstants.CONTENTS,
         new StandardAnalyzer(Version.LUCENE_36));
   }

   public TopDocs search( String searchQuery) 
      throws IOException, ParseException {
      query = queryParser.parse(searchQuery);
      return indexSearcher.search(query, LuceneConstants.MAX_SEARCH);
   }
   
   public TopDocs search(Query query) throws IOException, ParseException {
      return indexSearcher.search(query, LuceneConstants.MAX_SEARCH);
   }

   public Document getDocument(ScoreDoc scoreDoc) 
      throws CorruptIndexException, IOException {
      return indexSearcher.doc(scoreDoc.doc);	
   }

   public void close() throws IOException {
      indexSearcher.close();
   }
}

LuceneTester.java

This class is used to test the searching capability of the Lucene library.

package com.tutorialspoint.lucene;

import java.io.IOException;

import org.apache.lucene.document.Document;
import org.apache.lucene.index.Term;
import org.apache.lucene.queryParser.ParseException;
import org.apache.lucene.search.FuzzyQuery;
import org.apache.lucene.search.Query;
import org.apache.lucene.search.ScoreDoc;
import org.apache.lucene.search.TopDocs;

public class LuceneTester {
	
   String indexDir = "E:\\Lucene\\Index";
   String dataDir = "E:\\Lucene\\Data";
   Searcher searcher;

   public static void main(String[] args) {
      LuceneTester tester;
      try {
         tester = new LuceneTester();
         tester.searchUsingFuzzyQuery("cord3.txt");
      } catch (IOException e) {
         e.printStackTrace();
      } catch (ParseException e) {
         e.printStackTrace();
      }
   }
   private void searchUsingFuzzyQuery(String searchQuery)
      throws IOException, ParseException {
      searcher = new Searcher(indexDir);
      long startTime = System.currentTimeMillis();
      
      //create a term to search file name
      Term term = new Term(LuceneConstants.FILE_NAME, searchQuery);
      //create the term query object
      Query query = new FuzzyQuery(term);
      //do the search
      TopDocs hits = searcher.search(query);
      long endTime = System.currentTimeMillis();

      System.out.println(hits.totalHits +
         " documents found. Time :" + (endTime - startTime) + "ms");
      for(ScoreDoc scoreDoc : hits.scoreDocs) {
         Document doc = searcher.getDocument(scoreDoc);
         System.out.print("Score: "+ scoreDoc.score + " ");
         System.out.println("File: "+ doc.get(LuceneConstants.FILE_PATH));
      }
      searcher.close();
   }
}

Data & Index Directory Creation

We have used 10 text files from record1.txt to record10.txt containing names and other details of the students and put them in the directory E:\Lucene\Data. Test Data. An index directory path should be created as E:\Lucene\Index. After running the indexing program in the chapter Lucene - Indexing Process, you can see the list of index files created in that folder.

Running the Program

Once you are done with the creation of the source, the raw data, the data directory, the index directory and the indexes, you can proceed by compiling and running your program. To do this, keep LuceneTester.Java file tab active and use either the Run option available in the Eclipse IDE or use Ctrl + F11 to compile and run your LuceneTesterapplication. If your application runs successfully, it will print the following message in Eclipse IDE's console −

10 documents found. Time :78ms
Score: 1.3179655 File: E:\Lucene\Data\record3.txt
Score: 0.790779 File: E:\Lucene\Data\record1.txt
Score: 0.790779 File: E:\Lucene\Data\record2.txt
Score: 0.790779 File: E:\Lucene\Data\record4.txt
Score: 0.790779 File: E:\Lucene\Data\record5.txt
Score: 0.790779 File: E:\Lucene\Data\record6.txt
Score: 0.790779 File: E:\Lucene\Data\record7.txt
Score: 0.790779 File: E:\Lucene\Data\record8.txt
Score: 0.790779 File: E:\Lucene\Data\record9.txt
Score: 0.2635932 File: E:\Lucene\Data\record10.txt

lucene_query_programming.htm

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