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Lucene in 5 minutes

  • August 2, 2012 11:28 pm

http://www.lucenetutorial.com/lucene-in-5-minutes.html

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.

Directory index = new RAMDirectory();
IndexWriterConfig config = new IndexWriterConfig(Version.LUCENE_35, analyzer);

IndexWriter w = new IndexWriter(index, config);
addDoc(w, “Lucene in Action”);
addDoc(w, “Lucene for Dummies”);
addDoc(w, “Managing Gigabytes”);
addDoc(w, “The Art of Computer Science”);
w.close();
addDoc() takes a string and adds it to the index:

private static void addDoc(IndexWriter w, String value) throws IOException {
Document doc = new Document();
doc.add(new Field(“title”, value, Field.Store.YES, Field.Index.ANALYZED));
w.addDocument(doc);
}
}

addDoc() takes a string and adds it to the index:

private static void addDoc(IndexWriter w, String value) throws IOException {
Document doc = new Document();
doc.add(new Field(“title”, value, Field.Store.YES, Field.Index.ANALYZED));
w.addDocument(doc);
}
}

 

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_35, “title”, analyzer).parse(querystr);

 

3. Search

Using the Query we create a Searcher to search the index. Then instantiate a TopScoreDocCollector 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(“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.index.IndexReader;
import org.apache.lucene.index.IndexWriter;
import org.apache.lucene.index.IndexWriterConfig;
import org.apache.lucene.queryParser.ParseException;
import org.apache.lucene.queryParser.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_35);

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

IndexWriterConfig config = new IndexWriterConfig(Version.LUCENE_35, analyzer);

IndexWriter w = new IndexWriter(index, config);
addDoc(w, “Lucene in Action”);
addDoc(w, “Lucene for Dummies”);
addDoc(w, “Managing Gigabytes”);
addDoc(w, “The Art of Computer Science”);
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_35, “title”, analyzer).parse(querystr);

// 3. search
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 results
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(“title”));
}

// searcher can only be closed when there
// is no need to access the documents any more.
searcher.close();
}

private static void addDoc(IndexWriter w, String value) throws IOException {
Document doc = new Document();
doc.add(new Field(“title”, value, Field.Store.YES, Field.Index.ANALYZED));
w.addDocument(doc);
}
}

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

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