W3C Document Object Model (DOM)

XML Documents are treated as a tree of nodes
Every item is a "node"
Child elements and enclosed text are subnodes
W3C DOM Site: http://www.w3.org/DOM/
DOM Java Language Binding:
http://www.w3.org/TR/DOM-Level-2-Core/java-binding.html

The W3C XML DOM Objects

Element - An Element
Attribute - An attribute
Text - Text content of an element or attribute
CDATAsection - CDATA section
EntityReference - Reference to an entity
Entity - Indication of a parsed or unparsed entity
ProcessingInstruction - A processing instruction
Comment - Content of an XML comment
Document - The Document object
DocumentType - Reference to the <!DOCTYPE> element
DocumentFragment - Reference to a fragment of a document
Notation - Holder for a notation

Node-related Objects

Node - A single node in the document tree.
NodeList - A list of node objects.
NamedNodeMap - Allows interaction and access by name to the collection of attributes

XML Document as a Tree of Nodes

   <?xml version="1.0" encoding="UTF-8"?>
   <DOCUMENT>
      <GREETING>Hello from XML</GREETING>
      <MESSAGE>Welcome to Programing XML in Java</MESSAGE>
   </DOCUMENT>

Levels of DOM

Level 0 - Early versions of DOM in web browsers
Level 1 - It concentrates on the HTML and XML document models:

http://www.w3.org/TR/REC-DOM-Level-1/

Level 2 - It defines a set of objects and interfaces for accessing and manipulating document object. It includes a style sheet object model.

Document Object Model (DOM) Level 2 Core Specification:
http://www.w3.org/TR/DOM-Level-2-Core/

Level 3 - It will address document loading and saving, as well as content models (such as DTDs and schemas) with document validation support.

Document Object Model (DOM) Level 3 Core Specification
http://www.w3.org/TR/DOM-Level-3-Core/

DOM XML Parsers

Oracle XML parser for Java
http://technet.oracle.com/tech/xml/parser_java2/index.htm
Xerces Java Parser
http://xml.apache.org/xerces-j/index.html
IBM XML4J Parser
http://alphaworks.ibm.com/tech/xml4j
Sun JAXP
http://java.sun.com/xml/download.html
TurboPower XML Partner
http://www.turbopower.com/products/xmlpartner/

Working with DOM

Problem: Print the <students> element count of this XML file:

   <?xml version="1.0"?> 
   <course>
      <name id="csci_2962">Programming XML in Java</name>
      <teacher id="jp">
         <name>John Punin</name>
      </teacher>
      <student id="js">
         <name>John Smith</name>
         <hw1>30</hw1>
         <hw2>70</hw2>
         <project>80</project>
         <final>85</final>
      </student>
      <student id="gl">
         <name>George Lucas</name>
         <hw1>80</hw1>
         <hw2>90</hw2>
         <project>100</project>
         <final>40</final>
      </student>
      <student id="lr">
         <name>Elizabeth Roberts</name>
         <hw1>60</hw1>
         <hw2>95</hw2>
         <project>50</project>
         <final>90</final>
      </student>
   </course>

Using Xerces XML Parser

   import org.w3c.dom.*;
   import org.apache.xerces.parsers.DOMParser;

   public class DOMCountNames
   {
      public static void main(String[] args)
      {
         try{
	    DOMParser parser = new DOMParser();
	    parser.parse(args[0]);
	    Document doc = parser.getDocument();
	    .
	    .
            .
         }
         catch(Exception e){
            e.printStackTrace(System.err);
	 }
      }
   }

The DOMParser Class

Xerces 1.3.1 Package org.w3c.dom http://xml.apache.org/apiDocs/org/w3c/dom/package-summary.html
Complete Xerces API documentation
http://xml.apache.org/apiDocs/index.html
DOMParser class is derived from the XMLParser class

     java.lang.Object
     |
     +--org.apache.xerces.framework.XMLParser
        |
        +--org.apache.xerces.parsers.DOMParser

parse() method parses the input source given by a system identifier
Document getDocument() method returns the document itself

Document Interface Methods

Attr createAttribute(String name)
Creates an attribute of the given name
Element createElement(String tagName)
Creates an element of the type given
Text createTextNode(String data)
Creates a Text Node
Element getDocumentElement()
Gets the root element of the document
Element getElementById(String elementId) Get the element with the given ID
NodeList getElementsByTagName(String tagname)
Returns a NodeList of all the elements with a given tag name

NodeList Interface Methods

int getLength()
Gets the number of nodes in this list
Node item(int index)
Gets the item at the specified index value in the collection

Using Xerces XML Parser (2)

   import org.w3c.dom.*;
   import org.apache.xerces.parsers.DOMParser;

   public class DOMCountNames
   {
      public static void main(String[] args)
      {
         try{
	    DOMParser parser = new DOMParser();
	    parser.parse(args[0]);
	    Document doc = parser.getDocument();
	    NodeList nodelist = doc.getElementsByTagName("student");
	    System.out.println(args[0] + " has " + nodelist.getLength() 
		                       + " <student> elements.");
	 } 
         catch(Exception e){
	    e.printStackTrace(System.err);
	 }
      }
   }

Compiling and Running DOMCountNames example

javac -classpath ":xerces.jar" DOMCountNames.java
java -classpath ":xerces.jar" DOMCountNames students.xml

     students.xml has 3 <student> elements.

xerces.jar, DOMCountNames.java, DOMCountNames.class and students.xml are in the same directory

Node Interface Methods

NamedNodeMap getAttributes()
Gets a NamedNodeMap containing the attributes of this node
NodeList getChildNodes()
Gets a NodeList that contains all children of this node
String getLocalName()
Gets the local name of the node
String getNodeName()
Gets the name of this node
String getNodeValue()
Gets the value of this node
Node getParentNode()
Gets the parent of this node
short getNodeType()
Gets a code representing the type of the node

Node Types

static short ATTRIBUTE_NODE
static short CDATA_SECTION_NODE
static short COMMENT_NODE
static short DOCUMENT_FRAGMENT_NODE
static short DOCUMENT_NODE
static short DOCUMENT_TYPE_NODE
static short ELEMENT_NODE
static short ENTITY_NODE
static short ENTITY_REFERENCE_NODE
static short NOTATION_NODE
static short PROCESSING_INSTRUCTION_NODE
static short TEXT_NODE

Traversing an Entire Document

Problem: Print a list of the Elements of this XML file

   <?xml version="1.0"?> 
   <course>
      <name id="csci_2962">Programming XML in Java</name>
      <teacher id="jp">
         <name>John Punin</name>
      </teacher>
      <student id="js">
         <name>John Smith</name>
         <hw1>30</hw1>
         <hw2>70</hw2>
         <project>80</project>
         <final>85</final>
      </student>
      <student id="gl">
         <name>George Lucas</name>
         <hw1>80</hw1>
         <hw2>90</hw2>
         <project>100</project>
         <final>40</final>
      </student>
      <student id="lr">
         <name>Elizabeth Roberts</name>
         <hw1>60</hw1>
         <hw2>95</hw2>
         <project>50</project>
         <final>90</final>
      </student>
    </course>

Traversing an Entire Document (2)

   import org.w3c.dom.*;
   import org.apache.xerces.parsers.DOMParser;

   class DisplayElements
   {
      public static void displayDocument(String uri)
      {
         try{
            DOMParser parser = new DOMParser();
	    parser.parse(uri);
	    Document doc = parser.getDocument();
	    display_names(doc);
         }
         catch(Exception e){
	    e.printStackTrace(System.err);
         }
      }

      public static void display_names(Node node)
      {
         .
         .
         .
      }
   }

public class DOMNameElements
{
   public static void main(String[] args)
   {
      DisplayElements.displayDocument(args[0]);
   }
}

Traversing an Entire Document - Using Recursion (3)

Handling Document Nodes:

   public static void display_names(Node node)
   {
      if(node == null) {
	 return;
      }
      int type = node.getNodeType();
      switch (type) {
         case Node.DOCUMENT_NODE: {
            display_names(((Document)node).getDocumentElement());
	    break;
         }
         case Node.ELEMENT_NODE: {
            .
            .
            .
	    break;
         }   
      }
   }

Traversing an Entire Document - Using Recursion (4)

Handling Element Nodes:

   case Node.ELEMENT_NODE: {
      System.out.println("Element : " + node.getNodeName());

      NodeList childNodes = node.getChildNodes();	
      if(childNodes != null) {
         int length = childNodes.getLength();
         for (int loopIndex = 0; loopIndex < length ; loopIndex++)
         {
            display_names(childNodes.item(loopIndex));
         }
      }
      break;
   }

Putting all together

 import org.w3c.dom.*;
 import org.apache.xerces.parsers.DOMParser;

 class DisplayElements
 {
    public static void displayDocument(String uri)
    {
       try{
	  DOMParser parser = new DOMParser();
	  parser.parse(uri);
	  Document doc = parser.getDocument();
	  display_names(doc);
       } 
       catch (Exception e) {
          e.printStackTrace(System.err);
       }
    }

    public static void display_names(Node node)
    {
       if(node == null) {
	  return;
       }
       int type = node.getNodeType();
       switch (type) {
          case Node.DOCUMENT_NODE: {
	     display_names(((Document)node).getDocumentElement());
	     break;
	  }
	  case Node.ELEMENT_NODE: {
	     System.out.println("Element : " + node.getNodeName());
		
	     NodeList childNodes = node.getChildNodes();	
	     if(childNodes != null) {
	        int length = childNodes.getLength();
	        for (int loopIndex = 0; loopIndex < length ; loopIndex++)
	        {
	           display_names(childNodes.item(loopIndex));
	        }
	     }
	     break;
	  }   
       }
    }
 }

 public class DOMNameElements
 {
    public static void main(String[] args)
    {
       DisplayElements.displayDocument(args[0]);
    }
 }

Compiling and Running DOMNameElements example

javac -classpath ":xerces.jar" DOMNameElements.java
java -classpath ":xerces.jar" DOMNameElements students.xml

   Element : course
   Element : name
   Element : teacher
   Element : student
   Element : name
   Element : hw1
   Element : hw2
   Element : project
   Element : final
   Element : student
   Element : name
   Element : hw1
   Element : hw2
   Element : project
   Element : final
   Element : student
   Element : name
   Element : hw1
   Element : hw2
   Element : project
   Element : final

xerces.jar, DOMNameElements.java, DOMNameElements.class and students.xml are in the same directory

Working with DOM (Handling Nodes)

Problem: Print a list of Students Average and Course Average

   <?xml version="1.0"?> 
   <course>
      <name id="csci_2962">Programming XML in Java</name>
      <teacher id="jp">
         <name>John Punin</name>
      </teacher>
      <student id="js">
         <name>John Smith</name>
         <hw1>30</hw1>
         <hw2>70</hw2>
         <project>80</project>
         <final>85</final>
      </student>
      <student id="gl">
         <name>George Lucas</name>
         <hw1>80</hw1>
         <hw2>90</hw2>
         <project>100</project>
         <final>40</final>
      </student>
      <student id="lr">
         <name>Elizabeth Roberts</name>
         <hw1>60</hw1>
         <hw2>95</hw2>
         <project>50</project>
         <final>90</final>
      </student>
   </course>

Creating DOMParser and Document

   import org.w3c.dom.*;
   import org.apache.xerces.parsers.DOMParser;

   class Grades
   { 
      public static void computeGrades(String uri)
      {
         try{
            DOMParser parser = new DOMParser();
            parser.parse(uri);
            Document doc = parser.getDocument();
            traverse_tree(doc);
            compute_final_grades();
         } 
	 catch(Exception e){
            e.printStackTrace(System.err);
         }
      }
      .
      .
      .
   }

   public class DOMGrades
   {   
      public static void main(String[] args)
      {
         Grades.computeGrades(args[0]);
      }
   }

Handling Document Node, Element Node and Text Node

   static float grades[][] = new float[100][5];
   static int nstudent = 0;
   static int gi = -1;

   private static void traverse_tree(Node node)
   {
      if(node == null) {
         return;
      }
      int type = node.getNodeType();
      switch (type) {
         case Node.DOCUMENT_NODE: {
            traverse_tree(((Document)node).getDocumentElement());
            break;
         }
         case Node.ELEMENT_NODE: {
            String elementName = node.getNodeName();
            gi = -1;
            if(elementName.equals("hw1"))
               gi = 0;
            else if(elementName.equals("hw2"))
               gi = 1;
            else if(elementName.equals("project"))
               gi = 2;
            else if(elementName.equals("final"))
               gi = 3;
            else if(elementName.equals("student"))
               nstudent++;

            NodeList childNodes = node.getChildNodes();	
            if(childNodes != null) {
               int length = childNodes.getLength();
               for (int loopIndex = 0; loopIndex < length ; loopIndex++)
               {
                  traverse_tree(childNodes.item(loopIndex));
               }
            }
            break;
         }
         case Node.TEXT_NODE: {
            String chData = node.getNodeValue().trim();
            if(chData.indexOf("\n") < 0 && chData.length() > 0) {
               if(gi >= 0)
               grades[nstudent-1][gi] = Integer.parseInt(chData);
            }
         }
      }
   }

Computing grades after tree traversal

   static float grades[][] = new float[100][5];
   static int nstudent = 0;

   private static void compute_final_grades()
   {
      float Ave = 0;
      int i = 0, j = 0;
      System.out.println("Grades");
      for(i = 0; i < nstudent ; i++) 
      {
         float total = 0;
         for(j = 0; j < 4; j++) {
            total += grades[i][j];
         }		
         grades[i][4] = total/4;
         Ave += grades[i][4];
         System.out.println("Student " + i + "=" + grades[i][4]);
      }
      Ave /= nstudent;
      System.out.println("Class Average =" + Ave);  
   }

Putting all together

   import org.w3c.dom.*;
   import org.apache.xerces.parsers.DOMParser;

   class Grades
   { 
      static float grades[][] = new float[100][5];
      static int nstudent = 0;
      static int gi = -1;

      public static void computeGrades(String uri)
      {
         try {
         DOMParser parser = new DOMParser();
         parser.parse(uri);
         Document doc = parser.getDocument();
         traverse_tree(doc);
         compute_final_grades();
         } catch (Exception e) {
            e.printStackTrace(System.err);
         }
      }

      private static void compute_final_grades()
      {
         float Ave = 0;
         int i = 0, j = 0;
         System.out.println("Grades");
         for(i = 0; i < nstudent ; i++) 
         {
            float total = 0;
            for(j = 0; j < 4; j++) {
               total += grades[i][j];
            }		
            grades[i][4] = total/4;
            Ave += grades[i][4];
            System.out.println("Student " + i + "=" + grades[i][4]);
         }
      Ave /= nstudent;
      System.out.println("Class Average =" + Ave);  
      }

      private static void traverse_tree(Node node)
      {
         if(node == null) {
            return;
         }
         int type = node.getNodeType();
         switch (type) {
            case Node.DOCUMENT_NODE: {
               traverse_tree(((Document)node).getDocumentElement());
               break;
            }
            case Node.ELEMENT_NODE: {
               String elementName = node.getNodeName();
               gi = -1;
               if(elementName.equals("hw1"))
                  gi = 0;
               else if(elementName.equals("hw2"))
                  gi = 1;
               else if(elementName.equals("project"))
                  gi = 2;
               else if(elementName.equals("final"))
                  gi = 3;
               else if(elementName.equals("student"))
                  nstudent++;

               NodeList childNodes = node.getChildNodes();	
               if(childNodes != null) {
                  int length = childNodes.getLength();
                  for (int loopIndex = 0; loopIndex < length ; loopIndex++)
                  {
                     traverse_tree(childNodes.item(loopIndex));
                  }
               }
               break;
            }
            case Node.TEXT_NODE: {
               String chData = node.getNodeValue().trim();
               if(chData.indexOf("\n") < 0 && chData.length() > 0) {
                  if(gi >= 0)
                  grades[nstudent-1][gi] = Integer.parseInt(chData);
               }
            }
         }
      }
   }

   public class DOMGrades
   {
      public static void main(String[] args)
      {
         Grades.computeGrades(args[0]);
      }
   }

Compiling and Running DOMGrades example

javac -classpath ":xerces.jar" DOMGrades.java
java -classpath ":xerces.jar" DOMGrades students.xml

     Grades
     Student 0=66.25
     Student 1=77.5
     Student 2=73.75
     Class Average =72.5

xerces.jar, DOMGrades.java, DOMGrades.class and students.xml are in the same directory

Working with DOM (Using Attributes)

Attr Interface Methods:

String getName()
Gets the name of this attribute
Element getOwnerElement()
Gets the Element node to which this attribute is attached
String getValue()
Gets the value of the attribute as a string

NamedNodeMap Interface Methods:

int getLength()
Returns the number of nodes in this map
Node getNamedItem(String name)
Gets a node indicated by name
Node item(int index)
Gets an item in the map by index

Working with DOM (Using Attributes) (2)

Problem: Compute the area of each of these figures

   <?xml version="1.0"?> 
   <figures>
      <circle x="20" y="10" r="20"/>
      <rectangle x="-3" y="4" w="5" h="36"/>
      <ellipse x="-5" y="6" w="30" h="50"/>
      <rectangle x="7" y="23" w="58" h="45"/>
      <circle x="-2" y="5" r="35"/>
      <ellipse x="-10" y="-8" w="45" h="30"/>
   </figures>

Working with DOM (Using Attributes) (3)

   case Node.ELEMENT_NODE: 
   {
      String elementName = node.getNodeName();
      NamedNodeMap attrs = node.getAttributes();
      if(elementName.equals("circle")) {
         Attr attrib = (Attr)attrs.getNamedItem("r");
         String sr = attrib.getValue();
         float radius = Float.valueOf(sr).floatValue();
         float area = (float)Math.PI*radius*radius;
         System.out.println("Circle : Radius = " + radius + 
                            " Area = " + area);
      }
   }

Putting all together

   import org.w3c.dom.*;
   import org.apache.xerces.parsers.DOMParser;

   class Figures
   { 
      public static void computeArea(String uri)
      {
         try{
            DOMParser parser = new DOMParser();
	    parser.parse(uri);
	    Document doc = parser.getDocument();
	    traverse_tree(doc);
	 }
         catch (Exception e) {
	    e.printStackTrace(System.err);
	 }
      }

      private static void traverse_tree(Node node)
      {
         if(node == null) {
            return;
	 }
         int type = node.getNodeType();
         switch (type) {
            case Node.DOCUMENT_NODE: {
	       traverse_tree(((Document)node).getDocumentElement());
	       break;
	    }
	    case Node.ELEMENT_NODE: {
	       String elementName = node.getNodeName();
	       NamedNodeMap attrs = node.getAttributes();
	       if(elementName.equals("circle")) {
		  Attr attrib = (Attr)attrs.getNamedItem("r");
		  String sr = attrib.getValue();
		  float radius = Float.valueOf(sr).floatValue();
		  float area = (float)Math.PI*radius*radius;
		  System.out.println("Circle : Radius = " + radius + " Area = " + area);
	       }
	       else if(elementName.equals("rectangle")) {
		  Attr attrib = (Attr)attrs.getNamedItem("w");
		  String sw = attrib.getValue();
		  attrib = (Attr)attrs.getNamedItem("h");
		  String sh = attrib.getValue();
		  float width = Float.valueOf(sw).floatValue();
		  float height = Float.valueOf(sh).floatValue();
		  float area = width * height;
		  System.out.println("Rectangle : Width = " + width +
			             " Height = " + height + " Area = " + area);
		}
		else if(elementName.equals("ellipse")) {
		  Attr attrib = (Attr)attrs.getNamedItem("w");
		  String sw = attrib.getValue();
		  attrib = (Attr)attrs.getNamedItem("h");
		  String sh = attrib.getValue();
		  float width = Float.valueOf(sw).floatValue();
		  float height = Float.valueOf(sh).floatValue();
		  float area = (float)Math.PI*(width/2)*(height/2);
		  System.out.println("Ellipse : Width = " + width +
		                     " Height = " + height + " Area = " + area); 
		}
                NodeList childNodes = node.getChildNodes();	
		if(childNodes != null) {
		   int length = childNodes.getLength();
		   for (int loopIndex = 0; loopIndex < length ; loopIndex++)
		   {
		      traverse_tree(childNodes.item(loopIndex));
		   }
		}
		break;
	     }
	  }
       }
    } 

    public class DOMFigures
    {
       public static void main(String[] args)
       {
	  Figures.computeArea(args[0]);
       }
    }

Compiling and Running DOMFigures example

javac -classpath ":xerces.jar" DOMFigures.java
java -classpath ":xerces.jar" DOMFigures figures.xml

     Circle : Radius = 20.0 Area = 1256.6371
     Rectangle : Width = 5.0 Height = 36.0 Area = 180.0
     Ellipse : Width = 30.0 Height = 50.0 Area = 1178.0973
     Rectangle : Width = 58.0 Height = 45.0 Area = 2610.0
     Circle : Radius = 35.0 Area = 3848.4512
     Ellipse : Width = 45.0 Height = 30.0 Area = 1060.2876

xerces.jar, DOMFigures.java, DOMFigures.class and figures.xml are in the same directory