What does this Lucene-related code actually do? - perl

Question

#usr/bin/perl
use Plucene::Document;
use Plucene::Document::Field;
use Plucene::Index::Writer;
use Plucene::Analysis::SimpleAnalyzer;
use Plucene::Search::HitCollector;
use Plucene::Search::IndexSearcher;
use Plucene::QueryParser;
my $content = "I am the law";
my $doc = Plucene::Document->new;
$doc->add(Plucene::Document::Field->Text(content => $content));
$doc->add(Plucene::Document::Field->Text(author => "Philip Johnson"));
my $analyzer = Plucene::Analysis::SimpleAnalyzer->new();
my $writer = Plucene::Index::Writer->new("my_index", $analyzer, 1);
$writer->add_document($doc);
undef $writer; # close
my $searcher = Plucene::Search::IndexSearcher->new("my_index");
my #docs;
my $hc = Plucene::Search::HitCollector->new(collect => sub {
my ($self, $doc, $score) = #_;
push #docs, $searcher->doc($doc);
});
$searcher->search_hc($query => $hc);
Try as I may, I don't understand what this code does. I understand the familiar Perl syntax and what's going on on that end...but what is a Lucene Document, Index::Writer - etc.? Most importantly, when I run this code I expect something to be generated...yet I see nothing.
I know what an Analyzer is...thanks to this doc linked to in CPAN: http://onjava.com/pub/a/onjava/2003/01/15/lucene.html?page=2. But I am just not getting why I run this code and it doesn't seem to DO anything...

Answer 1

Lucene is a search engine designed to search huge amounts of text very fast.
My perl is not strong, but from what I understand from Lucene objects:
my $content = "I am the law";
my $doc = Plucene::Document->new;
$doc->add(Plucene::Document::Field->Text(content => $content));
$doc->add(Plucene::Document::Field->Text(author => "Philip Johnson"));
This part creates a new document object and adds two text fields to it, content and author, in preparation to add it to an lucene index file as searchable data.
my $analyzer = Plucene::Analysis::SimpleAnalyzer->new();
my $writer = Plucene::Index::Writer->new("my_index", $analyzer, 1);
$writer->add_document($doc);
undef $writer; # close
This part creates the index files and adds the previously created document do that index. At this point, you should have a "my_index" folder with several index files in it, in your application directory, with docs's data in it as searchable text.
my $searcher = Plucene::Search::IndexSearcher->new("my_index");
my #docs;
my $hc = Plucene::Search::HitCollector->new(collect => sub {
my ($self, $doc, $score) = #_;
push #docs, $searcher->doc($doc);
});
$searcher->search_hc($query => $hc);
This part attempts to search the index file created above for the same document data you just used to create the index file. Presumably, you'll have your search results in #docs at this point, which you might want to display to user (tho it is not, in this sample).
This seems to be a "hello world" application for Lucene usage in perl. In real-life applications, I dont see a scenario where you would create the index file and then search it from same piece of code.

Answer 2

Where did you get this code from? It is a copy of the code in the Synopsis at the start of the Plucene POD documentation.
I guess it was an attempt by someone to begin learning about Plucene. The code in a module's synopsis isn't necessarily meant to achieve something useful on its own.
As the documentation you refer to says, Lucene is a Java library that adds text indexing and searching capabilities to an application. It is not a complete application that one can just download, install, and run.
Where did you get the idea that you should run the code you show?