As we discussed in the previous walkthrough, the IndexFiles class creates a Lucene Index.
Lets take a look at how it does this.
The first substantial thing the main function does is instantiate an instance
of IndexWriter. It passes a string called "index" and a new instance of a class called
"StandardAnalyzer". The "index" string is the name of the directory that all index information
should be stored in. Because we're not passing any path information, one must assume this
will be created as a subdirectory of the current directory (if does not already exist). On
some platforms this may actually result in it being created in other directories (such as
the user's home directory).
The IndexWriter is the main class responsible for creating indicies. 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 create it, otherwise it will refresh the index living at that path. You
must a also pass an instance of org.apache.analysis.Analyzer.
The Analyzer, in this case, the Stop Analyzer is little more than a standard Java
Tokenizer, converting all strings to lowercase and filtering out useless words from the index.
By useless words I mean common language words such as articles (a,an,the) and other words that
would be useless for searching. 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 English and German.
Looking down further in the file, you should see the indexDocs() code. This recursive function
simply crawls the directories and uses FileDocument to create Document objects. The Document
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 indexWriter. Take a look inside FileDocument. Its
not particularly complicated, it just adds fields to the Document.
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 IndexHTML class. It is
a bit more complex but builds upon this example.
