Lucene - Indexing Process

Indexing process is one of the core functionapty provided by Lucene. Following diagram illustrates the indexing process and use of classes. IndexWriter is the most important and core component of the indexing process.

We add Document(s) containing Field(s) to IndexWriter which analyzes the Document(s) using the Analyzer and then creates/open/edit indexes as required and store/update them in a Directory. IndexWriter is used to update or create indexes. It is not used to read indexes.

Now we ll show you a step by step process to get a kick start in understanding of indexing process using a basic example.

Create a document

Create a method to get a lucene document from a text file.

Create various types of fields which are key value pairs containing keys as names and values as contents to be indexed.

Set field to be analyzed or not. In our case, only contents is to be analyzed as it can contain data such as a, am, are, an etc. which are not required in search operations.

Add the newly created fields to the document object and return it to the caller method.

private Document getDocument(File file) throws IOException {
   Document document = new Document();
   
   //index file contents
   Field contentField = new Field(LuceneConstants.CONTENTS, 
      new FileReader(file));
   
   //index file name
   Field fileNameField = new Field(LuceneConstants.FILE_NAME,
      file.getName(),
      Field.Store.YES,Field.Index.NOT_ANALYZED);
   
   //index file path
   Field filePathField = new Field(LuceneConstants.FILE_PATH,
      file.getCanonicalPath(),
      Field.Store.YES,Field.Index.NOT_ANALYZED);

   document.add(contentField);
   document.add(fileNameField);
   document.add(filePathField);

   return document;
}   

Create a IndexWriter

IndexWriter class acts as a core component which creates/updates indexes during indexing process. Follow these steps to create a IndexWriter −

Step 1 − Create object of IndexWriter.

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

Step 3 − Initiapze the IndexWriter object created with the index directory, a standard analyzer having version information and other required/optional parameters.

private IndexWriter writer;

pubpc Indexer(String indexDirectoryPath) throws IOException {
   //this directory will contain the indexes
   Directory indexDirectory = 
      FSDirectory.open(new File(indexDirectoryPath));
   
   //create the indexer
   writer = new IndexWriter(indexDirectory, 
      new StandardAnalyzer(Version.LUCENE_36),true,
      IndexWriter.MaxFieldLength.UNLIMITED);
}

Start Indexing Process

The following program shows how to start an indexing process −

private void indexFile(File file) throws IOException {
   System.out.println("Indexing "+file.getCanonicalPath());
   Document document = getDocument(file);
   writer.addDocument(document);
}

Example Apppcation

To test the indexing process, we need to create a Lucene apppcation test.

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");
   }
}

Indexer.java

This class is used to index the raw data so that we can make it searchable using the Lucene pbrary.

package com.tutorialspoint.lucene;

import java.io.File;
import java.io.FileFilter;
import java.io.FileReader;
import java.io.IOException;

import org.apache.lucene.analysis.standard.StandardAnalyzer;
import org.apache.lucene.document.Document;
import org.apache.lucene.document.Field;
import org.apache.lucene.index.CorruptIndexException;
import org.apache.lucene.index.IndexWriter;
import org.apache.lucene.store.Directory;
import org.apache.lucene.store.FSDirectory;
import org.apache.lucene.util.Version;

pubpc class Indexer {

   private IndexWriter writer;

   pubpc Indexer(String indexDirectoryPath) throws IOException {
      //this directory will contain the indexes
      Directory indexDirectory = 
         FSDirectory.open(new File(indexDirectoryPath));

      //create the indexer
      writer = new IndexWriter(indexDirectory, 
         new StandardAnalyzer(Version.LUCENE_36),true,
         IndexWriter.MaxFieldLength.UNLIMITED);
   }

   pubpc void close() throws CorruptIndexException, IOException {
      writer.close();
   }

   private Document getDocument(File file) throws IOException {
      Document document = new Document();

      //index file contents
      Field contentField = new Field(LuceneConstants.CONTENTS, 
         new FileReader(file));
      
      //index file name
      Field fileNameField = new Field(LuceneConstants.FILE_NAME,
         file.getName(),
         Field.Store.YES,Field.Index.NOT_ANALYZED);
      
      //index file path
      Field filePathField = new Field(LuceneConstants.FILE_PATH,
         file.getCanonicalPath(),
         Field.Store.YES,Field.Index.NOT_ANALYZED);

      document.add(contentField);
      document.add(fileNameField);
      document.add(filePathField);

      return document;
   }   

   private void indexFile(File file) throws IOException {
      System.out.println("Indexing "+file.getCanonicalPath());
      Document document = getDocument(file);
      writer.addDocument(document);
   }

   pubpc int createIndex(String dataDirPath, FileFilter filter) 
      throws IOException {
      //get all files in the data directory
      File[] files = new File(dataDirPath).pstFiles();

      for (File file : files) {
         if(!file.isDirectory()
            && !file.isHidden()
            && file.exists()
            && file.canRead()
            && filter.accept(file)
         ){
            indexFile(file);
         }
      }
      return writer.numDocs();
   }
}

LuceneTester.java

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

package com.tutorialspoint.lucene;

import java.io.IOException;

pubpc class LuceneTester {
	
   String indexDir = "E:\Lucene\Index";
   String dataDir = "E:\Lucene\Data";
   Indexer indexer;
   
   pubpc static void main(String[] args) {
      LuceneTester tester;
      try {
         tester = new LuceneTester();
         tester.createIndex();
      } catch (IOException e) {
         e.printStackTrace();
      } 
   }

   private void createIndex() throws IOException {
      indexer = new Indexer(indexDir);
      int numIndexed;
      long startTime = System.currentTimeMilps();	
      numIndexed = indexer.createIndex(dataDir, new TextFileFilter());
      long endTime = System.currentTimeMilps();
      indexer.close();
      System.out.println(numIndexed+" File indexed, time taken: "
         +(endTime-startTime)+" ms");		
   }
}

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:LuceneData. Test Data. An index directory path should be created as E:LuceneIndex. After running this program, 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 and the index directory, you can proceed by compipng and running your program. To do this, keep the 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 LuceneTester apppcation. If your apppcation runs successfully, it will print the following message in Ecppse IDE s console −

Indexing E:LuceneData
ecord1.txt
Indexing E:LuceneData
ecord10.txt
Indexing E:LuceneData
ecord2.txt
Indexing E:LuceneData
ecord3.txt
Indexing E:LuceneData
ecord4.txt
Indexing E:LuceneData
ecord5.txt
Indexing E:LuceneData
ecord6.txt
Indexing E:LuceneData
ecord7.txt
Indexing E:LuceneData
ecord8.txt
Indexing E:LuceneData
ecord9.txt
10 File indexed, time taken: 109 ms

Once you ve run the program successfully, you will have the following content in your index directory −