Lucene Java Example

By Susam Pal on 10 Apr 2010

Here is a simple program I wrote that makes use of Lucene Java 3.0.1:

package in.susam;

import java.io.File;
import java.io.IOException;

import org.apache.lucene.index.IndexWriter;
import org.apache.lucene.queryParser.ParseException;
import org.apache.lucene.queryParser.QueryParser;
import org.apache.lucene.search.IndexSearcher;
import org.apache.lucene.search.ScoreDoc;
import org.apache.lucene.search.TopDocs;
import org.apache.lucene.store.FSDirectory;
import org.apache.lucene.analysis.standard.StandardAnalyzer;
import org.apache.lucene.util.Version;
import org.apache.lucene.document.Document;
import org.apache.lucene.document.Field;

public class LuceneDemo
{
    static final String INDEX_DIR = "index1";
 
    public static void main(String[] args) throws Exception {
        write();
        search("content", "integer");
        search("tags", "rhyme");
    }
    
    static void write() throws IOException {
        // Create index
        IndexWriter writer = new IndexWriter(
                FSDirectory.open(new File(INDEX_DIR)),
                new StandardAnalyzer(Version.LUCENE_30),
                true,
                IndexWriter.MaxFieldLength.UNLIMITED);
 
        Document doc;
        String field;
        String text;
 
        // Add first document
        doc = new Document();

        field = "title";
        text = "Humpty Dumpty sat on a wall";
        doc.add(new Field(field, text, Field.Store.YES, Field.Index.ANALYZED));

        field = "content";
        text = "Humpty Dumpty sat on a wall.\n" +
               "Humpty Dumpty had a great fall;\n" +
               "All the King's horses and all the King's men,\n" +
               "Couldn't put Humpty together again.";
        doc.add(new Field(field, text, Field.Store.YES, Field.Index.ANALYZED));
        
        field = "tags";
        text = "rhyme";
        doc.add(new Field(field, text, Field.Store.YES, Field.Index.ANALYZED));
        
        writer.addDocument(doc);

        // Add second document
        doc = new Document();

        field = "title";
        text = "Jack and Jill went up the hill";
        doc.add(new Field(field, text, Field.Store.YES, Field.Index.ANALYZED));
        
        field = "content";
        text = "Jack and Jill went up the hill\n" +
               "To fetch a pail of water.\n" +
               "Jack fell down and broke his crown,\n" +
               "And Jill came tumbling after.\n"; 
        doc.add(new Field(field, text, Field.Store.YES, Field.Index.ANALYZED));

        field = "tags";
        text = "rhyme";
        doc.add(new Field(field, text, Field.Store.YES, Field.Index.ANALYZED));
        
        writer.addDocument(doc);
        
        // Add third document
        doc = new Document();
        
        field = "title";
        text = "Fermat's Last Theorem";
        doc.add(new Field(field, text, Field.Store.YES, Field.Index.ANALYZED));

        field = "content";
        text = "In number theory, Fermat's Last Theorem states that no " +
               "three positive integers a, b, and c can satisfy the " +
               "equation for a^n + b^n = c^n for any integer value of n " +
               "greater than two.";
        doc.add(new Field(field, text, Field.Store.YES, Field.Index.ANALYZED));
        
        field = "tags";
        text = "math, theorem";
        doc.add(new Field(field, text, Field.Store.YES, Field.Index.ANALYZED));
        
        writer.addDocument(doc);
        
        // Add fourth document
        doc = new Document();
      
        field = "title";
        text = "Euler's theorem";
        doc.add(new Field(field, text, Field.Store.YES, Field.Index.ANALYZED));
        
        field = "content";
        text = "Euler's theorem states that if n is a positive integer and " +
               "a is a positive integer coprime to n, then a^phi(n) = 1 " +
               "(mod n) where phi(n) is Euler's totient function.";
        doc.add(new Field(field, text, Field.Store.YES, Field.Index.ANALYZED));
        
        field = "tags";
        text = "math, theorem";
        doc.add(new Field(field, text, Field.Store.YES, Field.Index.ANALYZED));

        writer.addDocument(doc);

        writer.close();
    }
    
    static void search(String field, String query) throws IOException,
                                                          ParseException {
        IndexSearcher searcher = new IndexSearcher(
                FSDirectory.open(new File(INDEX_DIR)), true);
        QueryParser parser = new QueryParser(
                Version.LUCENE_30, field,
                new StandardAnalyzer(Version.LUCENE_30));
        TopDocs docs = searcher.search(parser.parse(query), 10);
        System.out.println("Query: '" + query + "' in '" + field + "'");
        System.out.println("Total hits: " + docs.totalHits);
        System.out.println("");
        for (int i = 0; i < docs.scoreDocs.length; i++) {
            ScoreDoc hit = docs.scoreDocs[i];
            Document doc = searcher.doc(hit.doc);
            System.out.println("#" + i);
            System.out.println("title: " + doc.get("title"));
            System.out.println("content: " + doc.get("content"));
            System.out.println("tags: " + doc.get("tags"));
            System.out.println("id: " + hit.doc);
            System.out.println("score: " + hit.score);
            System.out.println();
        }
    }
}

Here is the output when the above code is compiled and run:

Query: 'integer' in 'content'
Total hits: 2

#0
title: Euler's theorem
content: Euler's theorem states that if n is a positive integer and a is a positive integer coprime to n, then a^phi(n) = 1 (mod n) where phi(n) is Euler's totient function.
tags: math, theorem
id: 3
score: 0.34144828

#1
title: Fermat's Last Theorem
content: In number theory, Fermat's Last Theorem states that no three positive integers a, b, and c can satisfy the equation for a^n + b^n = c^n for any integer value of n greater than two.
tags: math, theorem
id: 2
score: 0.24144039

Query: 'rhyme' in 'tags'
Total hits: 2

#0
title: Humpty Dumpty sat on a wall
content: Humpty Dumpty sat on a wall.
Humpty Dumpty had a great fall;
All the King's horses and all the King's men,
Couldn't put Humpty together again.
tags: rhyme
id: 0
score: 1.287682

#1
title: Jack and Jill went up the hill
content: Jack and Jill went up the hill
To fetch a pail of water.
Jack fell down and broke his crown,
And Jill came tumbling after.

tags: rhyme
id: 1
score: 1.287682
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