2002-01-26 10:01:32 -05:00
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<?xml version="1.0"?>
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<document>
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<properties>
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<author email="acoliver@apache.org">Andrew C. Oliver</author>
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2005-02-14 11:48:47 -05:00
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<title>Apache Lucene - Basic Demo Sources Walkthrough</title>
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</properties>
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<body>
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<section name="About the Code">
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<p>
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In this section we walk through the sources behind the basic Lucene demo such as where to
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find it, its parts and their function. This section is intended for Java developers
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wishing to understand how to use Apache Lucene in their applications.
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</p>
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</section>
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<section name="Location of the source">
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<p>
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Relative to the directory created when you extracted Lucene or retreived it from Subversion, you
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should see a directory called "src" which in turn contains a directory called "demo".
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This is the root for all of the Lucene demos. Under this directory is org/apache/lucene/demo,
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this is where all the Java sources live.
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</p>
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<p>
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Within this directory you should see the IndexFiles class we executed earlier. Bring that
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up in vi or your alternative text editor and lets take a look at it.
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</p>
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</section>
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<section name="IndexFiles">
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<p>
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As we discussed in the previous walkthrough, the IndexFiles class creates a Lucene Index.
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Lets take a look at how it does this.
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</p>
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<p>
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The first substantial thing the main function does is instantiate an instance
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of IndexWriter. It passes a string called "index" and a new instance of a class called
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"StandardAnalyzer". The "index" string is the name of the directory that all index information
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should be stored in. Because we're not passing any path information, one must assume this
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will be created as a subdirectory of the current directory (if it does not already exist). On
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some platforms this may actually result in it being created in other directories (such as
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the user's home directory).
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</p>
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<p>
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The <b>IndexWriter</b> is the main class responsible for creating indicies. To use it you
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must instantiate it with a path that it can write the index into, if this path does not
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exist it will create it, otherwise it will refresh the index living at that path. You
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must a also pass an instance of <b>org.apache.lucene.analysis.Analyzer</b>.
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</p>
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<p>
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The <b>Analyzer</b>, in this case, the <b>StandardAnalyzer</b> is little more than a standard Java
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Tokenizer, converting all strings to lowercase and filtering out useless words and characters from the index.
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By useless words and characters I mean common language words such as articles (a, an, the, etc.) and other
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strings that would be useless for searching (e.g. <b>'s</b>) . It should be noted that there are different
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rules for every language, and you should use the proper analyzer for each. Lucene currently
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provides Analyzers for English and German, more can be found in the Lucene Sandbox.
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</p>
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<p>
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Looking down further in the file, you should see the indexDocs() code. This recursive function
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simply crawls the directories and uses FileDocument to create Document objects. The Document
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is simply a data object to represent the content in the file as well as its creation time and
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location. These instances are added to the indexWriter. Take a look inside FileDocument. It's
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not particularly complicated, it just adds fields to the Document.
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</p>
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<p>
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As you can see there isn't much to creating an index. The devil is in the details. You may also
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wish to examine the other samples in this directory, particularly the IndexHTML class. It is
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a bit more complex but builds upon this example.
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</p>
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</section>
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<section name="Searching Files">
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<p>
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The SearchFiles class is quite simple. It primarily collaborates with an IndexSearcher, StandardAnalyzer
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(which is used in the IndexFiles class as well) and a QueryParser. The query parser is constructed
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with an analyzer used to interperate your query in the same way the Index was interperated: finding
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the end of words and removing useless words like 'a', 'an' and 'the'. The Query object contains the
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results from the QueryParser which is passed to the searcher. The searcher results are returned in
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a collection of Documents called "Hits" which is then iterated through and displayed to the user.
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</p>
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</section>
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<section name="The Web example...">
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<p>
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<a href="demo3.html">read on>>></a>
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</p>
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</section>
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</body>
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</document>
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