Lucene - PrefixQuery

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PrefixQuery class is used to match documents whose index start with a specified string.

Class Declaration

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

public class PrefixQuery
   extends AutomatonQuery

Class Constructors

S.No.	Constructor & Description
1	PrefixQuery(Term prefix) Constructs a query for terms starting with prefix.
2	PrefixQuery(Term prefix, MultiTermQuery.RewriteMethod rewriteMethod) Constructs a query for terms starting with prefix using a defined RewriteMethod

Class Methods

S.No.	Method & Description
1	boolean equals(Object obj) Override and implement query instance equivalence properly in a subclass.
2	Term getPrefix() Returns the prefix of this query.
3	int hashCode() Override and implement query hash code properly in a subclass.
4	static Automaton toAutomaton(BytesRef prefix) Build an automaton accepting all terms with the specified prefix.
5	String toString(String field) Prints a user-readable version of this query.

Methods Inherited

This class inherits methods from the following classes −

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

Usage of PrefixQuery

private void searchUsingPrefixQuery(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 PrefixQuery(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.println("File: "+ doc.get(LuceneConstants.FILE_PATH));
   }
}

Example Application

To test search using PrefixQuery, 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.PrefixQuery;
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.searchUsingPrefixQuery("record1");
      } catch (IOException e) {
         e.printStackTrace();
      } catch (ParseException e) {
         e.printStackTrace();
      }
   }

   private void searchUsingPrefixQuery(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 PrefixQuery(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.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

2 hits documents found. Time :87ms
File: D:\lucene\Data\record1.txt
File: D:\lucene\Data\record10.txt