More DOM

1
More DOM
2
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, dont 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

3
Overview

• There are three basic kinds of operations
• Creating a new DOM
• Modifying the structure of a DOM
• Modifying the content of a DOM
• Creating a new DOM requires a few extra methods
  just to get started
• Afterwards, you can grow the DOM by modifying
  its structure and content

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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 (ParserConfiguratio
nException e) ...
5
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
• Ill just go through some of the more important
  methods briefly
• The details can be looked up in the API if needed

6
Creating structure

• The following are instance methods of Document
• public Element createElement(String tagName)
• public Element createElementNS(String
  namespaceURI,
  String qualifiedName)
• public Attr createAttribute(String name)
• public Attr createAttributeNS(String
  namespaceURI,
  String qualifiedName)
• public ProcessingInstruction createProcessingInstr
  uction
  (String target, String data)
• public EntityReference createEntityReference(Strin
  g name)
• The above may all throw a DOMException
• public Text createTextNode(String data)
• public Comment createComment(String data)

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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

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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)

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Method of Attr

• public void setValue(String value)
• This is the only method that modifies an Attr
  the rest just get information

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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 simpleits
  just a tree walk
• However, there are a lot of detailsvarious node
  types and so onso doing a good job isnt
  complicated, but it is lengthy

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The End