Lucene - Search Operation

The process of searching is one of the core functionapties provided by Lucene. Following diagram illustrates the process and its use. IndexSearcher is one of the core components of the searching process.

We first create Directory(s) containing indexes and then pass it to IndexSearcher which opens the Directory using IndexReader. Then we create a Query with a Term and make a search using IndexSearcher by passing the Query to the searcher. IndexSearcher returns a TopDocs object which contains the search details along with document ID(s) of the Document which is the result of the search operation.

We will now show you a step-wise approach and help you understand the indexing process using a basic example.

Create a QueryParser

QueryParser class parses the user entered input into Lucene understandable format query. Follow these steps to create a QueryParser −

Step 1 − Create object of QueryParser.

Step 2 − Initiapze the QueryParser object created with a standard analyzer having version information and index name on which this query is to be run.

QueryParser queryParser;

pubpc Searcher(String indexDirectoryPath) throws IOException {

   queryParser = new QueryParser(Version.LUCENE_36,
      LuceneConstants.CONTENTS,
      new StandardAnalyzer(Version.LUCENE_36));
}

Create a IndexSearcher

IndexSearcher class acts as a core component which searcher indexes created during indexing process. Follow these steps to create a IndexSearcher −

Step 1 − Create object of IndexSearcher.

Step 2 − Create a Lucene directory which should point to location where indexes are to be stored.

Step 3 − Initiapze the IndexSearcher object created with the index directory.

IndexSearcher indexSearcher;

pubpc Searcher(String indexDirectoryPath) throws IOException {
   Directory indexDirectory = 
      FSDirectory.open(new File(indexDirectoryPath));
   indexSearcher = new IndexSearcher(indexDirectory);
}

Make search

Follow these steps to make search −

Step 1 − Create a Query object by parsing the search expression through QueryParser.

Step 2 − Make search by calpng the IndexSearcher.search() method.

Query query;

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

Get the Document

The following program shows how to get the document.

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

Close IndexSearcher

The following program shows how to close the IndexSearcher.

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

Example Apppcation

Let us create a test Lucene apppcation to test searching process.

LuceneConstants.java

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

package com.tutorialspoint.lucene;

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

TextFileFilter.java

This class is used as a .txt file filter.

package com.tutorialspoint.lucene;

import java.io.File;
import java.io.FileFilter;

pubpc class TextFileFilter implements FileFilter {

   @Override
   pubpc boolean accept(File pathname) {
      return pathname.getName().toLowerCase().endsWith(".txt");
   }
}

Searcher.java

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

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;

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

   pubpc 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));
   }

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

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

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

LuceneTester.java

This class is used to test the searching capabipty of the Lucene pbrary.

package com.tutorialspoint.lucene;

import java.io.IOException;

import org.apache.lucene.document.Document;
import org.apache.lucene.queryParser.ParseException;
import org.apache.lucene.search.ScoreDoc;
import org.apache.lucene.search.TopDocs;

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

   pubpc static void main(String[] args) {
      LuceneTester tester;
      try {
         tester = new LuceneTester();
         tester.search("Mohan");
      } catch (IOException e) {
         e.printStackTrace();
      } catch (ParseException e) {
         e.printStackTrace();
      }
   }

   private void search(String searchQuery) throws IOException, ParseException {
      searcher = new Searcher(indexDir);
      long startTime = System.currentTimeMilps();
      TopDocs hits = searcher.search(searchQuery);
      long endTime = System.currentTimeMilps();

      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));
      }
      searcher.close();
   }	
}

Data & Index Directory Creation

We have used 10 text files named record1.txt to record10.txt containing names and other details of the students and put them in the directory E:LuceneData. Test Data. An index directory path should be created as E:LuceneIndex. After running the indexing program in the chapter Lucene - Indexing Process, you can see the pst 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 compipng and running your program. To do this, keep LuceneTester.Java file tab active and use either the Run option available in the Ecppse IDE or use Ctrl + F11 to compile and run your LuceneTesterapppcation. If your apppcation runs successfully, it will print the following message in Ecppse IDE s console −

1 documents found. Time :29 ms
File: E:LuceneData
ecord4.txt