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The logical representation of a {@link org.apache.lucene.document.Document} for indexing and searching.
The document package provides the user level logical representation of content to be indexed and searched. The
package also provides utilities for working with {@link org.apache.lucene.document.Document}s and {@link org.apache.lucene.document.Fieldable}s.
Document and Fieldable
A {@link org.apache.lucene.document.Document} is a collection of {@link org.apache.lucene.document.Fieldable}s. A
{@link org.apache.lucene.document.Fieldable} is a logical representation of a user's content that needs to be indexed or stored.
{@link org.apache.lucene.document.Fieldable}s have a number of properties that tell Lucene how to treat the content (like indexed, tokenized,
stored, etc.) See the {@link org.apache.lucene.document.Field} implementation of {@link org.apache.lucene.document.Fieldable}
for specifics on these properties.
Note: it is common to refer to {@link org.apache.lucene.document.Document}s having {@link org.apache.lucene.document.Field}s, even though technically they have
{@link org.apache.lucene.document.Fieldable}s.
Working with Documents
First and foremost, a {@link org.apache.lucene.document.Document} is something created by the user application. It is your job
to create Documents based on the content of the files you are working with in your application (Word, txt, PDF, Excel or any other format.)
How this is done is completely up to you. That being said, there are many tools available in other projects that can make
the process of taking a file and converting it into a Lucene {@link org.apache.lucene.document.Document}. To see an example of this,
take a look at the Lucene demo and the associated source code
for extracting content from HTML.
The {@link org.apache.lucene.document.DateTools} and {@link org.apache.lucene.document.NumberTools} classes are utility
classes to make dates, times and longs searchable (remember, Lucene only searches text).
The {@link org.apache.lucene.document.FieldSelector} class provides a mechanism to tell Lucene how to load Documents from
storage. If no FieldSelector is used, all Fieldables on a Document will be loaded. As an example of the FieldSelector usage, consider
the common use case of
displaying search results on a web page and then having users click through to see the full document. In this scenario, it is often
the case that there are many small fields and one or two large fields (containing the contents of the original file). Before the FieldSelector,
the full Document had to be loaded, including the large fields, in order to display the results. Now, using the FieldSelector, one
can {@link org.apache.lucene.document.FieldSelectorResult#LAZY_LOAD} the large fields, thus only loading the large fields
when a user clicks on the actual link to view the original content.
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