More DOM - Advance Java Web Technology - Lecture Slides, Slides of Computer Science

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More DOM

Manipulating DOM trees

• DOM, unlike SAX, gives you the ability to create and modify XML trees
• There are a few roadblocks along the way
  • Practically everything in the JAXP implementation is an interface, with a few abstract classes
  • Interfaces, such as Node, don’t have constructors; this makes it hard to get started
  • Since DOM was designed to be applicable from a number of languages, many things are not done “the Java way”
• Once you get past these problems, the individual methods are pretty straightforward - Even with straightforward methods, working with trees is seldom simple

Creating a DOM

import javax.xml.parsers.*; import org.w3c.dom.Document;

try { DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance(); DocumentBuilder builder = factory.newDocumentBuilder(); Document doc = builder.newDocument(); } catch (ParserConfigurationException e) { ... }

The rest of the methods

• Most of the other methods are either instance

methods of a Document object, or are

inherited from Node

• A few are from Attr, Text, Entity, and so on

• Almost all of these methods may throw a

DOMException

• I’ll just go through some of the more

important methods briefly

• The details can be looked up in the API if needed

Methods inherited from Node

• public Node appendChild(Node newChild)
• public Node insertBefore(Node newChild, Node refChild)
• public Node removeChild(Node oldChild)
• public Node replaceChild(Node newChild, Node oldChild)
• setNodeValue(String nodeValue)
  • What this does depends on the type of node
• public void setPrefix(String prefix)
• public void normalize()
  • Combines adjacent TextNodes

Methods of Element

• public void setAttribute(String name, String value)
• public Attr setAttributeNode(Attr newAttr)
• public void setAttributeNodeNS(String namespaceURI, String qualifiedName, String value)
• public Attr setAttributeNodeNS(Attr newAttr)
• public void removeAttribute(String name)
• public void removeAttributeNS(String namespaceURI, String localName)
• public Attr removeAttributeNode(Attr oldAttr)

Writing out the DOM as XML

• There are no Java-supplied methods for

writing out a DOM as XML

• Writing out a DOM is conceptually simple—it’s

just a tree walk

• However, there are a lot of details—various node

types and so on—so doing a good job isn’t

complicated, but it is lengthy

The End