Lucene - Update Document Operation

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Update document is another important operation as part of indexing process. This operation is used when already indexed contents are updated and indexes become invalid. This operation is also known as re-indexing.

We update Document(s) containing Field(s) to IndexWriter where IndexWriter is used to update indexes.

We will now show you a step-wise approach and help you understand how to update document using a basic example.

Update a Document to an Index

Follow this step to update a document to an index −

Step 1 − Create a method to update a Lucene document from an updated text file.

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

   //update indexes for file contents
   writer.updateDocument(new Term 
      (LuceneConstants.CONTENTS, 
      new FileReader(file)),document); 
   writer.close();
}   

Create an IndexWriter

Follow these steps to create an IndexWriter −

Step 1 − IndexWriter class acts as a core component which creates/updates indexes during the indexing process.

Step 2 − Create object of IndexWriter.

Step 3 − Create a Lucene directory which should point to location where indexes are to be stored.

Step 4 − Initialize the IndexWriter object created with the index directory, a standard analyzer having version information and other required/optional parameters.

private IndexWriter writer;

public 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);
}

Update document and start reindexing process

Following are the two ways to update the document.

• updateDocument(Term, Document) − Delete the document containing the term and add the document using the default analyzer (specified when index writer is created).

• updateDocument(Term, Document,Analyzer) − Delete the document containing the term and add the document using the provided analyzer.

private void indexFile(File file) throws IOException {
   System.out.println("Updating index for "+file.getCanonicalPath());
   updateDocument(file);   
}

Example Application

To test the indexing process, let us create a Lucene application test.

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;
}

TextFileFilter.java

This class is used as a .txt file filter.

package com.tutorialspoint.lucene;

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

public class TextFileFilter implements FileFilter {

   @Override
   public 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 library.

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;

public class Indexer {

   private IndexWriter writer;

   public 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);
   }

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

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

      //update indexes for file contents
      writer.updateDocument(
         new Term(LuceneConstants.FILE_NAME,
         file.getName()),document); 
      writer.close();
   }  

   private void indexFile(File file) throws IOException {
      System.out.println("Updating index: "+file.getCanonicalPath());
      updateDocument(file);      
   }

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

      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 capability of the Lucene library.

package com.tutorialspoint.lucene;

import java.io.IOException;

public class LuceneTester {
	
   String indexDir = "E:\\Lucene\\Index";
   String dataDir = "E:\\Lucene\\Data";
   Indexer indexer;
   
   public 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.currentTimeMillis();	
      numIndexed = indexer.createIndex(dataDir, new TextFileFilter());
      long endTime = System.currentTimeMillis();
      indexer.close();
   }
}

Data & Index Directory Creation

Here, 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 this program, 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 and the index directory, you can proceed with the compiling and running of 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 −

Updating index for E:\Lucene\Data\record1.txt
Updating index for E:\Lucene\Data\record10.txt
Updating index for E:\Lucene\Data\record2.txt
Updating index for E:\Lucene\Data\record3.txt
Updating index for E:\Lucene\Data\record4.txt
Updating index for E:\Lucene\Data\record5.txt
Updating index for E:\Lucene\Data\record6.txt
Updating index for E:\Lucene\Data\record7.txt
Updating index for E:\Lucene\Data\record8.txt
Updating index for E:\Lucene\Data\record9.txt
10 File indexed, time taken: 109 ms

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