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<h1>
Apache Lucene - Basic Demo Sources Walk-through
</h1>
<div id="minitoc-area">
<ul class="minitoc">
<li>
<a href="#About the Code">About the Code</a>
</li>
<li>
<a href="#Location of the source">Location of the source</a>
</li>
<li>
<a href="#IndexFiles">IndexFiles</a>
</li>
<li>
<a href="#Searching Files">Searching Files</a>
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<li>
<a href="#The Web example...">The Web example...</a>
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<a name="N10013"></a><a name="About the Code"></a>
<h2 class="boxed">About the Code</h2>
<div class="section">
<p>
In this section we walk through the sources behind the command-line Lucene demo: where to find them,
their parts and their function. This section is intended for Java developers wishing to understand
how to use Lucene in their applications.
</p>
</div>
<a name="N1001C"></a><a name="Location of the source"></a>
<h2 class="boxed">Location of the source</h2>
<div class="section">
<p>
Relative to the directory created when you extracted Lucene or retrieved it from Subversion, you
should see a directory called <span class="codefrag">src</span> which in turn contains a directory called
<span class="codefrag">demo</span>. This is the root for all of the Lucene demos. Under this directory is
<span class="codefrag">org/apache/lucene/demo</span>. This is where all the Java sources for the demos live.
</p>
<p>
Within this directory you should see the <span class="codefrag">IndexFiles.java</span> class we executed earlier.
Bring it up in <span class="codefrag">vi</span> or your editor of choice and let's take a look at it.
</p>
</div>
<a name="N10037"></a><a name="IndexFiles"></a>
<h2 class="boxed">IndexFiles</h2>
<div class="section">
<p>
As we discussed in the previous walk-through, the <span class="codefrag">IndexFiles</span> class creates a Lucene
Index. Let's take a look at how it does this.
</p>
<p>
The first substantial thing the <span class="codefrag">main</span> function does is instantiate <span class="codefrag">IndexWriter</span>. It passes the string
"<span class="codefrag">index</span>" and a new instance of a class called <span class="codefrag">StandardAnalyzer</span>.
The "<span class="codefrag">index</span>" string is the name of the filesystem directory where all index information
should be stored. Because we're not passing a full path, this will be created as a subdirectory of
the current working directory (if it does not already exist). On some platforms, it may be created
in other directories (such as the user's home directory).
</p>
<p>
The <span class="codefrag">IndexWriter</span> is the main
class responsible for creating indices. To use it you must instantiate it with a path that it can
write the index into. If this path does not exist it will first create it. Otherwise it will
refresh the index at that path. You can also create an index using one of the subclasses of <span class="codefrag">Directory</span>. In any case, you must also pass an
instance of <span class="codefrag">org.apache.lucene.analysis.Analyzer</span>.
</p>
<p>
The particular <span class="codefrag">Analyzer</span> we
are using, <span class="codefrag">StandardAnalyzer</span>, is
little more than a standard Java Tokenizer, converting all strings to lowercase and filtering out
useless words and characters from the index. By useless words and characters I mean common language
words such as articles (a, an, the, etc.) and other strings that would be useless for searching
(e.g. <b>'s</b>) . It should be noted that there are different rules for every language, and you
should use the proper analyzer for each. Lucene currently provides Analyzers for a number of
different languages (see the <span class="codefrag">*Analyzer.java</span> sources under <a href="http://svn.apache.org/repos/asf/lucene/java/trunk/contrib/analyzers/src/java/org/apache/lucene/analysis/">contrib/analyzers/src/java/org/apache/lucene/analysis</a>).
</p>
<p>
Looking further down in the file, you should see the <span class="codefrag">indexDocs()</span> code. This recursive
function simply crawls the directories and uses <span class="codefrag">FileDocument</span> to create <span class="codefrag">Document</span> objects. The <span class="codefrag">Document</span> is simply a data object to
represent the content in the file as well as its creation time and location. These instances are
added to the <span class="codefrag">indexWriter</span>. Take a look inside <span class="codefrag">FileDocument</span>. It's not particularly
complicated. It just adds fields to the <span class="codefrag">Document</span>.
</p>
<p>
As you can see there isn't much to creating an index. The devil is in the details. You may also
wish to examine the other samples in this directory, particularly the <span class="codefrag">IndexHTML</span> class. It is a bit more
complex but builds upon this example.
</p>
</div>
<a name="N100AE"></a><a name="Searching Files"></a>
<h2 class="boxed">Searching Files</h2>
<div class="section">
<p>
The <span class="codefrag">SearchFiles</span> class is
quite simple. It primarily collaborates with an <span class="codefrag">IndexSearcher</span>, <span class="codefrag">StandardAnalyzer</span>
(which is used in the <span class="codefrag">IndexFiles</span> class as well) and a
<span class="codefrag">QueryParser</span>. The
query parser is constructed with an analyzer used to interpret your query text in the same way the
documents are interpreted: finding the end of words and removing useless words like 'a', 'an' and
'the'. The <span class="codefrag">Query</span> object contains
the results from the <span class="codefrag">QueryParser</span> which is passed to
the searcher. Note that it's also possible to programmatically construct a rich <span class="codefrag">Query</span> object without using the query
parser. The query parser just enables decoding the <a href="queryparsersyntax.html">Lucene query
syntax</a> into the corresponding <span class="codefrag">Query</span> object. Search can be executed in
two different ways:
<ul>
<li>Streaming: A <span class="codefrag">HitCollector</span> subclass
simply prints out the document ID and score for each matching document.</li>
<li>Paging: Using a <span class="codefrag">TopDocCollector</span>
the search results are printed in pages, sorted by score (i. e. relevance).</li>
</ul>
</p>
</div>
<a name="N100FB"></a><a name="The Web example..."></a>
<h2 class="boxed">The Web example...</h2>
<div class="section">
<p>
<a href="demo3.html">read on&gt;&gt;&gt;</a>
</p>
</div>
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