Big Java, 4th Edition

Chapter 23. XML

CHAPTER GOALS

• Understanding XML elements and attributes

• Understanding the concept of an XML parser

• Being able to read and write XML documents

• Being able to design Document Type Definitions for XML documents

In this chapter, you will learn about the Extensible Markup Language (XML), a mechanism for encoding data that is independent of any programming language. XML allows you to encode complex data in a form that the recipient can easily parse. XML is very popular for data exchange. It is simple enough that a wide variety of programs can easily generate XML data. XML data has a nested structure, so you can use it to describe hierarchical data sets—for example, an invoice that contains many items, each of which consists of a product and a quantity. Because the XML format is standardized, libraries for parsing the data are widely available and—as you will see in this chapter—easy to use for a programmer.

It is particularly easy to read and write XML documents in Java. In fact, it is generally easier to use XML than it is to use an "ad hoc" file format. Thus, using XML makes your programs easier to write and more professional.

XML Tags and Documents

Advantages of XML

To understand the advantages of using XML for encoding data, let's look at a typical example. We will encode product descriptions, so that they can be transferred to another computer. Your first attempt might be a naïve encoding like this:

Toaster
29.95

In contrast, here is an XML encoding of the same data:

<product> ...