mirror of https://github.com/apache/lucene.git
135 lines
7.0 KiB
XML
135 lines
7.0 KiB
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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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<title>Jakarta 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 Web Application demo.
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Where to find it, its parts, and their function. This section is intended for Java developers
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wishing to understand how to use Jakarta Lucene in their applications or for those involved
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in deploying web applications based on Lucene.
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</p>
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</section>
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<section name="Location of the source (developers/deployers)">
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<p>
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Relative the directory created when you extracted Lucene or retreived it from CVS, you
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should see a directory called "src" which in turn contains a directory called "jsp".
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This is the root for all of the Lucene web demo.
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</p>
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<p>
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Within this directory you should see the index.jsp class. Bring this up in vi or your
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editor of choice.
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</p>
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</section>
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<section name="index.jsp (developers/deployers)">
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<p>
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This jsp page is pretty boring by itself. All it does is include a header, display a form and
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include a footer. If you look at the form, it has two fields: query (where you enter your
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search criteria) and maxresults where you specify the number of results per page. If you look
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at the form tag, you'll notice it uses the get method as opposed to the post. While this is
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considered deprecated functionality by the latest w3c specs, its unlikely to go away due to the
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usefulness of being able to bookmark things like searches. By the structure of this JSP it should
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be easy to customize it without even editing this particular file. You could simply change the
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header and footer. Let's look at the header.jsp (located in the same directory) next.
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</p>
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</section>
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<section name="header.jsp (developers/deployers)">
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<p>
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The header is also very simple by itself. The only thing it does is include the configuration.jsp
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(which you looked at in the last section of this guide) and set the title and a brief header. This
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would be a good place to put your own custom HTML to "pretty" things up a bit. We won't cover the
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footer because all it does is display the footer and close your tags. Let's look at the results.jsp,
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the meat of this application next.
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</p>
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</section>
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<section name="results.jsp (developers)">
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<p>
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The results.jsp had a lot more functionality. Much of it is for paging the search results we'll not
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cover this as its commented well enough. It does not peform any optimizations such as caching results,
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etc. as that would make this a more complex example. The first thing in this page is the actual imports
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for the Lucene classes and Lucene demo classes. These classes are loaded from the jars included in the
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WEB-INF/lib directory in the final war file.
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</p>
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<p>
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You'll notice that this file includes the same header and footer as the "index.jsp". From there the jsp
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constructs an IndexSearcher with the "indexLocation" that was specified in the "configuration.jsp". If there
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is an error of any kind in opening the index, it is diplayed ot the user and a boolean flag is set to tell
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the rest of the sections of the jsp not to continue.
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</p>
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<p>
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From there, this jsp attempts to get the search criteria, the start index (used for paging) and the maximum
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number of results per page. If the maximum results per page is not set or not valid then it and the
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start index are set to default values. If only the start index is invalid it is set to a default value. If
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the criteria isn't provided then a servlet error is thrown (it is assumed that this is the result of url tampering
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or some form of browser malfunction).
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</p>
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<p>
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The jsp moves on to construct a StandardAnalyzer just as in the simple demo, to analyze the search critieria, it
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is passed to the QueryParser along with the criteria to construct a Query object. You'll also notice the
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string literal "contents" included. This is to specify the search should include the the contents and not
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the title, url or some other field in the indexed documents. If there is any error in constructing a Query
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object an error is displayed to the user.
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</p>
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<p>
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In the next section of the jsp the IndexSearcher is asked to search given the query object. the results are
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returned in a collection called "hits". If the length property of the hits collection is 0 then an error
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is displayed to the user and the error flag is set.
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</p>
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<p>
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Finally the jsp iterates through the hits collection and displayed properties of the "Document" objects we talked
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about in the first walkthrough. These objects contain "known" fields specific to their indexer (in this case
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"IndexHTML" constructs a document with "url", "title" and "contents"). You'll notice that these results are paged
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but the search is repeated every time. This is an area where optimization could improve performance for large
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result sets.
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</p>
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</section>
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<section name="More sources (developers)">
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<p>
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There are additional sources used by the web app that were not specifically covered by either walkthrough. For
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example the HTML parser, the IndexHTML class and HTMLDocument class. These are very similar to the classes
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covered in the first example, however they have properties sepecific to parsing and indexing HTML. This is
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beyond our scope; however, by now you should feel like you're "getting started" with Lucene.
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</p>
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</section>
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<section name="Where to go from here? (Everyone!)">
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<p>
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There are a number of things this demo doesn't do or doesn't do quite right. For instance, you may
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have noticed that documents in the root context are unreachable (unless you reconfigure Tomcat to
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support that context or redirect to it), anywhere where the directory doesn't quite match the context mapping,
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you'll have a broken link in your results. If you want to index non-local files or have some other
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needs this isn't supported, plus there may be security issues with running the indexing application from
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your webapps directory. There are a number of things left for you the implementor or developer to do.
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</p>
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<p>
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In time some of these things may be added to Lucene as features (if you've got a good idea we'd love to hear it!),
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but for now: this is where you begin and the search engine/indexer ends. Lastly, one would assume you'd
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want to follow the above advice and customize the application to look a little more fancy than black on
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white with "Lucene Template" at the top. We'll see you on the Lucene Users' or Developers' mailing lists!
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</p>
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</section>
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<section name="When to contact the Author">
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<p>
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Please resist the urge to contact the authors of this document (without bribes of fame and fortune attached). First
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contact the <a href="http://jakarta.apache.org/site/mail.html">mailing lists</a>. That being said feedback,
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and modifications to this document and samples are ever so greatly appreciatedThey are just best sent to the
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lists so that everyone can share in them. Certainly you'll get the most help there as well.
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Thanks for understanding.
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</p>
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</section>
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</body>
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</document>
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