Chapter 11.5
XML and more
A Brief Introduction to XML
• XML (eXtensible Markup Language) is a syntax for
creating data representation languages.
• There are XML languages for representing
mathematical expressions (MathML), musical
notation (MusicXML), molecules and chemical
reactions (CML), vector graphics (SVG), and many
other kinds of information.
Basic XML Syntax
• If you know HTML, the language for writing
document looks a lot like an HTML document.
HTML is not itself an XML language, since it does
not follow all the strict XML syntax rules, but the
basic ideas are similar.
• A document is made up of elements, attributes,
and textual content.
Elements, Textual Content, Attributes
• An element starts with a tag, such as <curve> and
ends with a matching end-tag such as </curve>.
• Between the tag and end-tag is the textual content
of the element, which can consist of text and
nested elements.
• If an element has no content, then the opening tag
and end-tag can be combined into a single empty
tag (which ends with “/>”.)
• A tag can include attributes.
XML Syntax Rules
• Tag names and attribute names in XML are case sensitive.
• A name must begin with a letter and can contain letters,
digits and certain other characters.
• Spaces and ends-of-line are significant only in textual
content.
• Every tag must either be an empty tag or have a matching
end-tag.
• A document must have a root element , which contains all
the other elements.
• Every attribute must have a value, and that value must be
enclosed in quotation marks (“ or ‘)
• & is an escape char: &lt, &amp, &gt, &apos
Working With the DOM
• Java has a standard API for parsing and processing
XML Documents.
• Document Object Model , or DOM specifies how to
build data structures to represent XML documents,
and it specifies some standard methods for
accessing the data in that structure.
• The data structure is a kind of tree whose structure
mirrors the structure of the document.
• In Java, the DOM representation of an XML
document file can be created with just two
statements.
• Classes defined in the package javax.xml.parsers.
• The structure of the DOM data structure is defined
in the package org.w3c.dom.
• An object of type Document represents an entire
XML document. The return value of
docReader.parse() — xmldoc in the above
example—is of type Document.
xmldoc.getDocumentElement()
• element.getTagName() String: tag’s name
• element.getAttribute(attrName) String: attr value
• element.getTextContent() String: textual content
• element.getChildNodes() NodeList: child nodes
• element.getChildNodes() Nodelist: nodes
representing all elements that are nested inside
element and which have the given tag name.
<background red=’255’ green=’153’ blue=’51’/>
• This element might be encountered either while traversing
the document with getChildNodes() or in the result of a call
to getElementsByTagName("background").
• int r = Integer.parseInt( element.getAttribute("red") );
• int g = Integer.parseInt( element.getAttribute("green") );
• int b = Integer.parseInt( element.getAttribute("blue") );
• Color bgColor = new Color(r,g,b);
Serializing using XML