Lucene example

Asked by: stenton
Published on: 06:44/12.06.2008
Status: OPEN

Please give an example how to search with Lucene. Lets suppose I already have index stored. Should I use QueryParser to parse query from given string or should I construct Query as java objects?

Answer by: xpert
Posted on: 06:44/12.06.2008
Rating: 3 from possible 5 with 2 votes

Lets suppose you have stored the lucene index in the filesystem with FSDirectory in folder "c:\lucenefolder". Lets say you have field "titleField" for all documents with option Field.Store.YES.
You can use query parser to search for word "mp3" :

import org.apache.lucene.analysis.standard.StandardAnalyzer;
import org.apache.lucene.document.Document;
import org.apache.lucene.queryParser.QueryParser;
import org.apache.lucene.search.Hits;
import org.apache.lucene.search.IndexSearcher;
import org.apache.lucene.search.Searcher;
import org.apache.lucene.store.FSDirectory;

public class Dummy {
    public static void main(String[] args) throws Exception {
        String queryString = "mp3";
        Searcher s = new IndexSearcher(FSDirectory.getDirectory("c:\\lucenefolder"));
        final QueryParser parser = new QueryParser(
                "titleField", 
                new StandardAnalyzer());
        final Hits hits = s.search(parser.parse(queryString));
        int hitCount = hits.length();
        if (hitCount == 0) {
            System.out.println("No results for for \"" + queryString + "\"");
        } else {
            System.out.println("Matched results for \"" +  queryString + "\":");
            // Iterate the Hits object
            for (int i = 0; i < hitCount; i++) {
                Document doc = hits.doc(i);
                System.out.println("doc#" + (i + 1) + ". " + doc.get("titleField"));
            }
        }
    }
}

Another way to make the query is to build it by your self:

import org.apache.lucene.document.Document;
import org.apache.lucene.index.Term;
import org.apache.lucene.search.*;
import org.apache.lucene.store.FSDirectory;

public class Dummy {
    public static void main(String[] args) throws Exception {
        String queryString = "mp3";
        Searcher s = new IndexSearcher(FSDirectory.getDirectory("c:\\lucenefolder"));
        final Query q = new TermQuery(new Term("titleField",queryString));
        final Hits hits = s.search(q);
        int hitCount = hits.length();
        if (hitCount == 0) {
            System.out.println("No results for for \"" + queryString + "\"");
        } else {
            System.out.println("Matched results for \"" +  queryString + "\":");
            // Iterate the Hits object
            for (int i = 0; i < hitCount; i++) {
                Document doc = hits.doc(i);
                System.out.println("doc#" + (i + 1) + ". " + doc.get("titleField"));
            }
        }
    }
}

You can make query by java objects like this(result should contain both words mp3 and radio):

        final BooleanQuery q = new BooleanQuery();
        q.add(
                new TermQuery(new Term("titleField","mp3")), 
                BooleanClause.Occur.MUST
        );
        q.add(
                new TermQuery(new Term("titleField","radio")), 
                BooleanClause.Occur.MUST
        );

Query that issues result that contains word "mp3" or word "radio"

        final BooleanQuery q = new BooleanQuery();
        q.add(
                new TermQuery(new Term("titleField","mp3")), 
                BooleanClause.Occur.SHOULD
        );
        q.add(
                new TermQuery(new Term("titleField","radio")), 
                BooleanClause.Occur.SHOULD
        );