Lucene RAMDirectory Example

In this Lucene 6 tutorial, we will learn to use RAMDirectory to run quick examples of POCs because it is not intended to work with huge indexes.

Read More: Lucene 6 Hello World Project Setup

Table of Contents

Write index in RAMDirectory
Search index in RAMDirectory
Complete Example

Write index in RAMDirectory

Most of the things will remain same when you want to index your documents in RAM (as temporary memory). You only need to change from FSDirectory to RAMDirectory.

//Create RAMDirectory instance
RAMDirectory ramDir = new RAMDirectory();

//Builds an analyzer with the default stop words
Analyzer analyzer = new StandardAnalyzer();

try 
{
	// IndexWriter Configuration
	IndexWriterConfig iwc = new IndexWriterConfig(analyzer);
	iwc.setOpenMode(OpenMode.CREATE);

	//IndexWriter writes new index files to the directory
	IndexWriter writer = new IndexWriter(ramDir, iwc);

	//Create some docs with name and content
	indexDoc(writer, "document-1", "hello world");
	indexDoc(writer, "document-2", "hello happy world");
	indexDoc(writer, "document-3", "hello happy world");
	indexDoc(writer, "document-4", "hello hello world");

	//don't forget to close the writer
	writer.close();
} 
catch (IOException e) 
{
	//Any error goes here
	e.printStackTrace();
}

static void indexDoc(IndexWriter writer, String name, String content) throws IOException 
{
	Document doc = new Document();
	doc.add(new TextField("name", name, Store.YES));
	doc.add(new TextField("content", content, Store.YES));
	writer.addDocument(doc);
}

Search index in RAMDirectory

To search index from RAM:

• Create IndexReader using DirectoryReader.open(RAMDirectory).
• Use reader to create IndexSearcher instance.
• Use searcher.search(query, int) to search indexed docs.

//Create RAMDirectory instance
RAMDirectory ramDir = new RAMDirectory();

//Builds an analyzer with the default stop words
Analyzer analyzer = new StandardAnalyzer();

IndexReader reader = null;
try 
{
	//Create Reader
	reader = DirectoryReader.open(ramDir);
	
	//Create index searcher
	IndexSearcher searcher = new IndexSearcher(reader);
	
	//Build query
	QueryParser qp = new QueryParser("content", analyzer);
	Query query = qp.parse("happy");

	//Search the index
	TopDocs foundDocs = searcher.search(query, 10);
	
	// Total found documents
	System.out.println("Total Results :: " + foundDocs.totalHits);

	//Let's print found doc names and their content along with score 
	for (ScoreDoc sd : foundDocs.scoreDocs) 
	{
		Document d = searcher.doc(sd.doc);
		System.out.println("Document Name : " + d.get("name") 
					+ "  :: Content : " + d.get("content") 
					+ "  :: Score : " + sd.score);
	}
	//don't forget to close the reader
	reader.close();
} 
catch (IOException | ParseException e) 
{
	//Any error goes here
	e.printStackTrace();
}

Complete Example

This is the complete sourcecode of RAMDirectory example which first – index 4 docs with some content, second – search docs based on query.

package com.howtodoinjava.demo.lucene.misc;

import java.io.IOException;

import org.apache.lucene.analysis.Analyzer;
import org.apache.lucene.analysis.standard.StandardAnalyzer;
import org.apache.lucene.document.Document;
import org.apache.lucene.document.Field.Store;
import org.apache.lucene.document.TextField;
import org.apache.lucene.index.DirectoryReader;
import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.IndexWriter;
import org.apache.lucene.index.IndexWriterConfig;
import org.apache.lucene.index.IndexWriterConfig.OpenMode;
import org.apache.lucene.queryparser.classic.ParseException;
import org.apache.lucene.queryparser.classic.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.RAMDirectory;

public class RAMDirectoryExample 
{
	public static void main(String[] args) 
	{
		//Create RAMDirectory instance
		RAMDirectory ramDir = new RAMDirectory();
		
		//Builds an analyzer with the default stop words
		Analyzer analyzer = new StandardAnalyzer();
		
		//Write some docs to RAMDirectory
		writeIndex(ramDir, analyzer);
		
		//Search indexed docs in RAMDirectory
		searchIndex(ramDir, analyzer);
	}

	static void writeIndex(RAMDirectory ramDir, Analyzer analyzer) 
	{
		try 
		{
			// IndexWriter Configuration
			IndexWriterConfig iwc = new IndexWriterConfig(analyzer);
			iwc.setOpenMode(OpenMode.CREATE);

			//IndexWriter writes new index files to the directory
			IndexWriter writer = new IndexWriter(ramDir, iwc);

			//Create some docs with name and content
			indexDoc(writer, "document-1", "hello world");
			indexDoc(writer, "document-2", "hello happy world");
			indexDoc(writer, "document-3", "hello happy world");
			indexDoc(writer, "document-4", "hello hello world");

			//don't forget to close the writer
			writer.close();
		} 
		catch (IOException e) 
		{
			//Any error goes here
			e.printStackTrace();
		}
	}

	static void indexDoc(IndexWriter writer, String name, String content) throws IOException 
	{
		Document doc = new Document();
		doc.add(new TextField("name", name, Store.YES));
		doc.add(new TextField("content", content, Store.YES));
		writer.addDocument(doc);
	}
	
	static void searchIndex(RAMDirectory ramDir, Analyzer analyzer) 
	{
		IndexReader reader = null;
		try 
		{
			//Create Reader
			reader = DirectoryReader.open(ramDir);
			
			//Create index searcher
			IndexSearcher searcher = new IndexSearcher(reader);
			
			//Build query
			QueryParser qp = new QueryParser("content", analyzer);
			Query query = qp.parse("happy");

			//Search the index
			TopDocs foundDocs = searcher.search(query, 10);
			
			// Total found documents
			System.out.println("Total Results :: " + foundDocs.totalHits);

			//Let's print found doc names and their content along with score 
			for (ScoreDoc sd : foundDocs.scoreDocs) 
			{
				Document d = searcher.doc(sd.doc);
				System.out.println("Document Name : " + d.get("name") 
							+ "  :: Content : " + d.get("content") 
							+ "  :: Score : " + sd.score);
			}
			//don't forget to close the reader
			reader.close();
		} 
		catch (IOException | ParseException e) 
		{
			//Any error goes here
			e.printStackTrace();
		}
	}
}

Output:

Total Results :: 2
Document Name : document-2  :: Content : hello happy world  :: Score : 0.58446556
Document Name : document-3  :: Content : hello happy world  :: Score : 0.58446556

Drop me your questions in comments section.

Happy Learning !!