Java: Lucene: Simple In-Memory Search Example
Join the DZone community and get the full member experience.
Join For Free// Adapted from http://javatechniques.com/blog/lucene-in-memory-text-search-example
// Works with present APIs in Lucene 2.1.0
/**
* A simple example of an in-memory search using Lucene.
*/
import java.io.IOException;
import java.io.StringReader;
import org.apache.lucene.search.Hits;
import org.apache.lucene.search.Query;
import org.apache.lucene.document.Field;
import org.apache.lucene.search.Searcher;
import org.apache.lucene.index.IndexWriter;
import org.apache.lucene.document.Document;
import org.apache.lucene.store.RAMDirectory;
import org.apache.lucene.search.IndexSearcher;
import org.apache.lucene.queryParser.QueryParser;
import org.apache.lucene.queryParser.ParseException;
import org.apache.lucene.analysis.standard.StandardAnalyzer;
public class InMemoryExample
{
public static void main(String[] args)
{
// Construct a RAMDirectory to hold the in-memory representation
// of the index.
RAMDirectory idx = new RAMDirectory();
try
{
// Make an writer to create the index
IndexWriter writer = new IndexWriter(idx, new StandardAnalyzer(), true);
// Add some Document objects containing quotes
writer.addDocument(createDocument("Theodore Roosevelt",
"It behooves every man to remember that the work of the "
+ "critic, is of altogether secondary importance, and that, "
+ "in the end, progress is accomplished by the man who does "
+ "things."));
writer.addDocument(createDocument("Friedrich Hayek",
"The case for individual freedom rests largely on the "
+ "recognition of the inevitable and universal ignorance "
+ "of all of us concerning a great many of the factors on "
+ "which the achievements of our ends and welfare depend."));
writer.addDocument(createDocument("Ayn Rand",
"There is nothing to take a man’s freedom away from "
+ "him, save other men. To be free, a man must be free "
+ "of his brothers."));
writer.addDocument(createDocument("Mohandas Gandhi",
"Freedom is not worth having if it does not connote "
+ "freedom to err."));
// Optimize and close the writer to finish building the index
writer.optimize();
writer.close();
// Build an IndexSearcher using the in-memory index
Searcher searcher = new IndexSearcher(idx);
// Run some queries
search(searcher, "freedom");
search(searcher, "free");
search(searcher, "progress or achievements");
searcher.close();
}
catch (IOException ioe)
{
// In this example we aren’t really doing an I/O, so this
// exception should never actually be thrown.
ioe.printStackTrace();
}
catch (ParseException pe)
{
pe.printStackTrace();
}
}
/**
* Make a Document object with an un-indexed title field and an indexed
* content field.
*/
private static Document createDocument(String title, String content)
{
Document doc = new Document();
// Add the title as an unindexed field…
doc.add(new Field("title", title, Field.Store.YES, Field.Index.NO));
// …and the content as an indexed field. Note that indexed
// Text fields are constructed using a Reader. Lucene can read
// and index very large chunks of text, without storing the
// entire content verbatim in the index. In this example we
// can just wrap the content string in a StringReader.
doc.add(new Field("content", new StringReader(content)));
return doc;
}
/**
* Searches for the given string in the "content" field
*/
private static void search(Searcher searcher, String queryString)
throws ParseException, IOException
{
// Build a Query object
QueryParser parser = new QueryParser("content", new StandardAnalyzer());
Query query = parser.parse(queryString);
// Search for the query
Hits hits = searcher.search(query);
// Examine the Hits object to see if there were any matches
int hitCount = hits.length();
if (hitCount == 0)
{
System.out.println("No matches were found for \"" + queryString + "\"");
}
else
{
System.out.println("Hits for \"" + queryString
+ "\" were found in quotes by:");
// Iterate over the Documents in the Hits object
for (int i = 0; i < hitCount; i++)
{
Document doc = hits.doc(i);
// Print the value that we stored in the "title" field. Note
// that this Field was not indexed, but (unlike the
// "contents" field) was stored verbatim and can be
// retrieved.
System.out.println(" " + (i + 1) + ". " + doc.get("title"));
}
}
System.out.println();
}
}
Opinions expressed by DZone contributors are their own.
Comments