Tutorials : Using FOP with Java

Benefits of FOP

How will this benefit me? Well, using FOP means that we could have a single formatter program capable of handling multiple output formats and multiple output devices. For the same data set, by providing different XSL-FO stylesheets, we can easily produce different formatted output. Instead of maintaining a multitude of programs for different formatted output there is only one application, this equates to less overhead. Because FOP is an output independent formatter, the formatting engine doesn't care about the final output format.

XSL-FO Introduction

XSL-FO is an XML based markup language to define the formatting of XML data for visible output. XSL-FO is the driving engine behind FOP. A detailed discussion of XSL-FO is beyond the scope of this article. However, we will learn as much as we need to get a head start with FOP. For a detailed discussion on XSL-FO refer to the resources provided at the end of this article.

XSL-FO can generally be classified as:

An XSL based markup language to define the formatting of XML data.
A W3C recommended standard.
The XSL FO documents are stored with .fo extension.
XSL defines a way to produce a FO document. So they are not the same thing.

XSL FO Document Structure

A very basic XSL FO document will look like this:

<?xml version="1.0" encoding="ISO-8859-1"?>
<fo:root xmlns:fo="http://www.w3.org/1999/XSL/Format">

<fo:layout-master-set>
  <fo:simple-page-master master-name="A4">
    <!-- Page template goes here -->
  </fo:simple-page-master>
</fo:layout-master-set>

<fo:page-sequence master-name="A4">
  <!-- Page content goes here -->
</fo:page-sequence>
</fo:root>

You should make note of following items in the above document:

The XSL FO document starts with a XML declaration and declares a "fo" namespace.

It contains a <fo:root> element.
<fo:layout-master-set> contains one or more page templates.
<fo:simple-page-master master-name="A4"> defines a single page template. Each simple page master has a unique name (A4 in this instance).
<fo:page-sequence master-name="A4"> element describes a single page content and refers to a master template(A4) to specify the layout.

XSL-FO Areas

XSL-FO defines a set of areas to display output. All the content of the document will be displayed in one of the defined areas following the layout specification for that particular area. Some of the more commonly used areas are:

Page: XSL FO formatted document is output to one or multiple pages.
Region: XSL FO Page can contain number of regions:
- region-body (the body of the page)
- region-before (the header of the page)
- region-after (the footer of the page)
- region-start (the left sidebar)
- region-end (the right sidebar)
Block: XSL FO Regions contain Block areas such as paragraph etc.
Flow: XSL FO Flows contain Blocks.

The Page contains Region and Region contains Flows and Flows contain Blocks.

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