Book Image

Lucene 4 Cookbook

By : Edwood Ng, Vineeth Mohan
Book Image

Lucene 4 Cookbook

By: Edwood Ng, Vineeth Mohan

Overview of this book

Table of Contents (16 chapters)
Lucene 4 Cookbook
About the Authors
About the Reviewers

Creating fields

We have learned that indexing information in Lucene requires the creation of document objects. A Lucene document contains one or more field where each one represents a single data point about the document. A field can be a title, description, article ID, and so on. In this section, we will show you the basic structure and how to create a field.

A Lucene field has three attributes:

  • Name

  • Type

  • Value

Name and value are self-explanatory. You can think of a name as a column name in a table, and value as a value in one of the records where record itself is a document. Type determines how the field is treated. You can set FieldType to control whether to store value, to index it or even tokenize text. A Lucene field can hold the following:

  • String

  • Reader or preanalyzed TokenStream

  • Binary(byte[])

  • Numeric value

How to do it...

This code snippet shows you how to create a simple TextField:

  Document doc = new Document();
  String text = "Lucene is an Information Retrieval library written in Java.";
  doc.add(new TextField("fieldname", text, Field.Store.YES));

How It Works

In this scenario, we create a document object, initialize a text, and add a field by creating a TextField object. We also configure the field to store a value so it can be retrieved during a search.

A Lucene document is a collection of field objects. A field is the name of the value pairs, which you may add to the document. A field is created by simply instantiating one of the Field classes. Field can be inserted into a document via the add method.