Apache Lucen is a full text-search library for java which helps
you add search capability to your application/website.
Note that Lucene is specifically an API, not an application.
Apache Lucene is a power full search library on which the
widely used search engines like Apache Solr,ElasticSearch are based
You can add contents to Lucene from various sources,like a SQL/NoSQL database, a filesystem, or even from websites.
Some Terminologies
Index
Lucene uses index called an inverted index, because it inverts
a page-centric data structure (page->words) to a keyword-centric
data structure (word->pages).
Document
An index consists of one or more Documents.
Indexing involves adding Documents to an IndexWriter,
and searching involves retrieving Documents from an index via an IndexSearcher.
Fields
A Document consists of one or more Fields. A Field is simply a name-value pair.
Let's get started:
For quickly getting started I am going to create an In-Memory Index.
Step-1
Create an empty Maven project using the following console command:
$ mvn archetype:create -DgroupId=demo.lucene -DartifactId=lucene-demo
Step-2
Add Lucene dependencies to pom.xml
file as defined below
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>demo.lucene</groupId>
<artifactId>lucene-demo</artifactId>
<version>1.0</version>
<name>Lucene-HelloWorld</name>
<description>Hello World Lucene Search Example</description>
<dependencies>
<dependency>
<groupId>org.apache.lucene</groupId>
<artifactId>lucene-core</artifactId>
<version>2.4.1</version>
</dependency>
<dependency>
<groupId>lucene</groupId>
<artifactId>lucene</artifactId>
<version>1.4.3</version>
</dependency>
</dependencies>
</project>
Step-3
Create a Java file HelloWorldLucene.java
class
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 {
// Specify the analyzer for tokenizing text.
// The same analyzer should be used for indexing and searching
StandardAnalyzer analyzer = new StandardAnalyzer(Version.LUCENE_40);
// 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();
//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);
// 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;
// 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("isbn") + "\t" + d.get("title"));
}
// reader can only be closed when there
// is no need to access the documents any more.
reader.close();
}
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));
// Use a string field for isbn because we don't want it tokenized
doc.add(new StringField("isbn", isbn, Field.Store.YES));
w.addDocument(doc);
}
}
Step-4
Compile project
$ mvn clean package
Step-5
Run Project
$ java -jar <jar_name> <Main-Class_name> <query_string>
In our case run command:
$ java -jar lucene-demo-1.0.jar HelloWorldLucen "lucene"
1 comments:
Great Article
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