DOM: Document Object Model
A DOM Document is a collection of nodes, or
pieces of information, organized in a hierarchy. This hierarchy allows a
developer to navigate around the tree looking for specific information.
Analyzing
the structure normally requires the entire document to be loaded and the
hierarchy to be built before any work is done. Because it is based on a
hierarchy of information, the DOM is said to be tree-based, or object-based.
DOM
create in build memory tree like structure, whenever it starts
Parsing, after completing parsing of entire file that tree throws to
application program to handle each and every events occurred in it.
Parsing a
file into a document:
It is three-step process. To work with the
information in an XML file, the file must be parsed to create a Document
object. The Document object is an interface, so it can't be instantiated
directly; generally, the application uses a factory instead. The exact process
varies from implementation to implementation, but the ideas are the same.
In the example Java environment, parsing the file
is a three-step process:
1. Create the DocumentBuilderFactory. This
object creates the DocumentBuilder.
2. Create the DocumentBuilder. The
DocumentBuilder does the actual parsing to create the Document object.
3. Parse
the file to create the Document object.
Now you can
start building the application
First, the
Java code imports the necessary classes, and then it creates the OrderProcessor
application. The Document object can be used later; the application defines it
outside the try-catch block. Within the try-catch block, the application
creates the DocumentBuilderFactory, which it then uses to create the
DocumentBuilder. Finally, the DocumentBuilder parses the file to create the
Document.
Once the
document is parsed and a Document is created, an application can step through
the structure to review, find, or display information. This navigation is the
basis for many operations that will be performed on a Document. Stepping
through the document begins with the root element. A well-formed document has
only one root element, also known as the DocumentElement. First the application
retrieves this element.
DOM
Example:
Input XML
File for parsing
<?xml version="1.0"
encoding="UTF-8"?>
<weather>
<day1>
<location>Vita</location>
<date>25/04/2013</date>
<temp>42'c</temp>
</day1>
</weather>
DOM Program
for XML File parsing
import java.io.File;
import javax.xml.parsers.*;
import org.w3c.dom.*;
public class Dom
{
public static void main(String args[])
{
try
{
File f=new
File("weather.xml");
DocumentBuilderFactory
dbf=DocumentBuilderFactory.newInstance();
DocumentBuilder
db=dbf.newDocumentBuilder();
Document
doc=db.parse(f);
System.out.println("RootNode="+doc.getDocumentElement().getNodeName());
}
catch(Exception e)
{ e.printStackTrace();
}
}
}
How to
compile and run Dom parser program.
Save these two programs in same
directory Jdk/bin
Compile all programs and run it
Your Output will display.
