Lucene in 5 minutes

Lucene in 5 minutes

Lucene makes it easy to add full-text search capability to your application. In fact, its so easy, I'm going to show you how in 5 minutes!

1. Index

For this simple case, we're going to create an in-memory index from some strings.

StandardAnalyzer analyzer = new StandardAnalyzer(Version.LUCENE_40);
Directory index = new RAMDirectory();

IndexWriterConfig config = new IndexWriterConfig(Version.LUCENE_40, analyzer);

IndexWriter w = new IndexWriter(index, config);
addDoc(w, "Lucene in Action", "193398817");
addDoc(w, "Lucene for Dummies", "55320055Z");
addDoc(w, "Managing Gigabytes", "55063554A");
addDoc(w, "The Art of Computer Science", "9900333X");
w.close();

addDoc() is what actually adds documents to the index:

private static void addDoc(IndexWriter w, String title, String isbn) throws IOException {
  Document doc = new Document();
  doc.add(new TextField("title", title, Field.Store.YES));
  doc.add(new StringField("isbn", isbn, Field.Store.YES));
  w.addDocument(doc);
}

Note the use of TextField for content we want tokenized, and StringField for id fields and the like, which we don't want tokenized.

2. Query

We read the query from stdin, parse it and build a lucene Query out of it.

String querystr = args.length > 0 ? args[0] : "lucene";
Query q = new QueryParser(Version.LUCENE_40, "title", analyzer).parse(querystr);

3. Search

Using the Query we create a Searcher to search the index. Then a TopScoreDocCollector is instantiated to collect the top 10 scoring hits.

int hitsPerPage = 10;
IndexReader reader = IndexReader.open(index);
IndexSearcher searcher = new IndexSearcher(reader);
TopScoreDocCollector collector = TopScoreDocCollector.create(hitsPerPage, true);
searcher.search(q, collector);
ScoreDoc[] hits = collector.topDocs().scoreDocs;

4. Display

Now that we have results from our search, we display the results to the user.

System.out.println("Found " + hits.length + " hits.");
for(int i=0;i<hits.length;++i) {
    int docId = hits[i].doc;
    Document d = searcher.doc(docId);
    System.out.println((i + 1) + ". " + d.get("isbn") + "\t" + d.get("title"));
}

Here's the app in its entirety. Download HelloLucene.java

import org.apache.lucene.analysis.standard.StandardAnalyzer;
import org.apache.lucene.document.Document;
import org.apache.lucene.document.Field;
import org.apache.lucene.document.StringField;
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.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.TopScoreDocCollector;
import org.apache.lucene.store.Directory;
import org.apache.lucene.store.RAMDirectory;
import org.apache.lucene.util.Version;

import java.io.IOException;

public class HelloLucene {
  public static void main(String[] args) throws IOException, ParseException {
    // 0. Specify the analyzer for tokenizing text.
    //    The same analyzer should be used for indexing and searching
    StandardAnalyzer analyzer = new StandardAnalyzer(Version.LUCENE_40);

    // 1. create the index
    Directory index = new RAMDirectory();

    IndexWriterConfig config = new IndexWriterConfig(Version.LUCENE_40, analyzer);

    IndexWriter w = new IndexWriter(index, config);
    addDoc(w, "Lucene in Action", "193398817");
    addDoc(w, "Lucene for Dummies", "55320055Z");
    addDoc(w, "Managing Gigabytes", "55063554A");
    addDoc(w, "The Art of Computer Science", "9900333X");
    w.close();

    // 2. query
    String querystr = args.length > 0 ? args[0] : "lucene";

    // the "title" arg specifies the default field to use
    // when no field is explicitly specified in the query.
    Query q = new QueryParser(Version.LUCENE_40, "title", analyzer).parse(querystr);

    // 3. search
    int hitsPerPage = 10;
    IndexReader reader = DirectoryReader.open(index);
    IndexSearcher searcher = new IndexSearcher(reader);
    TopScoreDocCollector collector = TopScoreDocCollector.create(hitsPerPage, true);
    searcher.search(q, collector);
    ScoreDoc[] hits = collector.topDocs().scoreDocs;
   
    // 4. display results
    System.out.println("Found " + hits.length + " hits.");
    for(int i=0;i

To use this app from the command line, type java HelloLucene <query>