Lucene - FuzzyQuery

---

---

FuzzyQuery class 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 org.apache.lucene.search.FuzzyQuery class −

public class FuzzyQuery
   extends MultiTermQuery

Class Fields

S.No.	Method & Description
1	static final int defaultMaxEdits
2	static final int defaultMaxExpansions
3	static final int defaultPrefixLength
4	static final boolean defaultTranspositions

Class Constructors

S.No.	Constructor & Description
1	FuzzyQuery(Term term) Calls FuzzyQuery(term, defaultMaxEdits).
2	FuzzyQuery(Term term, int maxEdits) Calls FuzzyQuery(term, maxEdits, defaultPrefixLength).
3	FuzzyQuery(Term term, int maxEdits, int prefixLength) Calls FuzzyQuery(term, maxEdits, prefixLength, defaultMaxExpansions, defaultTranspositions).
4	FuzzyQuery(Term term, int maxEdits, int prefixLength, int maxExpansions, boolean transpositions) Calls FuzzyQuery(Term, int, int, int, boolean, org.apache.lucene.search.MultiTermQuery.RewriteMethod) FuzzyQuery(term, maxEdits, prefixLength, maxExpansions, defaultRewriteMethod(maxExpansions))
5	FuzzyQuery(Term term, int maxEdits, int prefixLength, int maxExpansions, boolean transpositions, MultiTermQuery.RewriteMethod rewriteMethod) Create a new FuzzyQuery that will match terms with an edit distance of at most maxEdits to term.

Class Methods

S.No.	Method & Description
1	static MultiTermQuery.RewriteMethod defaultRewriteMethod(int maxExpansions) Creates a default top-terms blended frequency scoring rewrite with the given max expansions.
2	boolean equals(Object obj) Override and implement query instance equivalence properly in a subclass.
3	static int floatToEdits(float minimumSimilarity, int termLen) Helper function to convert from "minimumSimilarity" fractions to raw edit distances.
4	CompiledAutomaton getAutomata() Returns the compiled automata used to match terms.
5	static CompiledAutomaton getFuzzyAutomaton(String term, int maxEdits, int prefixLength, boolean transpositions) Returns the CompiledAutomaton internally used by FuzzyQuery to match terms.
6	int getMaxEdits()
7	int getPrefixLength() Returns the non-fuzzy prefix length.
8	Term getTerm() Returns the pattern term.
9	protected TermsEnum getTermsEnum(Terms terms, AttributeSource atts) Construct the enumeration to be used, expanding the pattern term.
10	boolean getTranspositions() Returns true if transpositions should be treated as a primitive edit operation.
11	int hashCode() Override and implement query hash code properly in a subclass.
12	String toString(String field) Prints a query to a string, with field assumed to be the default field and omitted.
13	void visit(QueryVisitor visitor) Recurse through the query tree, visiting any child queries.

Methods Inherited

This class inherits methods from the following classes −

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

Usage of FuzzyQuery

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));
   }
} 

Example Application

To test search using BooleanQuery, let us create a test Lucene application.

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.IOException;
import java.nio.file.Paths;
import java.text.ParseException;

import org.apache.lucene.analysis.standard.StandardAnalyzer;
import org.apache.lucene.document.Document;
import org.apache.lucene.index.CorruptIndexException;
import org.apache.lucene.index.DirectoryReader;
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.FSDirectory;
import org.apache.lucene.util.QueryBuilder;

public class Searcher {

   IndexSearcher indexSearcher;
   QueryBuilder queryBuilder;
   Query query;

   public Searcher(String indexDirectoryPath) 
      throws IOException {
      DirectoryReader indexDirectory = DirectoryReader.open(FSDirectory.open(Paths.get(indexDirectoryPath)));
      indexSearcher = new IndexSearcher(indexDirectory);
      StandardAnalyzer analyzer = new StandardAnalyzer();
      queryBuilder = new QueryBuilder(analyzer);
   }

   public TopDocs search( String searchQuery) 
      throws IOException, ParseException {
      query = queryBuilder.createPhraseQuery(LuceneConstants.CONTENTS, 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.storedFields().document(scoreDoc.doc);	
   }
}

LuceneTester.java

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

package com.tutorialspoint.lucene;

import java.io.IOException;
import java.text.ParseException;

import org.apache.lucene.document.Document;
import org.apache.lucene.index.Term;
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 = "D:\\Lucene\\Index";
   String dataDir = "D:\\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));
      }
   }
}

Data & Index Directory Creation

I've used 10 text files from record1.txt to record10.txt containing names and other details of the students and put them in the directory D:\Lucene\Data. Test Data. An index directory path should be created as D:\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 the 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 LuceneTester application. If your application runs successfully, it will print the following message in Eclipse IDE's console −

Output

1 hits documents found. Time :89ms
Score: 0.73515606 File: D:\lucene\Data\record3.txt