XML Parsing With DOM and Xerces (part 2) - The Writing On The Wall (
Page 2 of 9 )
Let's
begin by quickly revisiting the sample XML file used earlier:
<?xml version="1.0"?>
<inventory>
<!-- time to lock and load -->
<item>
<id>758</id>
<name>Rusty, jagged nails for nailgun</name>
<supplier>NailBarn, Inc.</supplier>
<cost currency="USD">2.99</cost>
A
<quantity alert="500">10000</quantity>
</item>
<item>
<id>6273</id>
<name>Power pack for death ray</name>
<supplier>QuakePower.domain.com</supplier>
<cost currency="USD">9.99</cost>
<quantity alert="20">10</quantity>
</item>
</inventory>
This next example ports the dynamically-printed tree structure you saw in a previous
example to work with a Web server.
import org.apache.xerces.parsers.DOMParser;
import org.xml.sax.SAXException;
import
org.w3c.dom.*;
import java.io.*;
public class MyFourthDomApp {
private Writer
out;
String Content = "";
// a counter for keeping track of the "tabs"
private int TabCounter = 0;
// constructor
public MyFourthDomApp (String
xmlFile, Writer out) {
this.out = out;
// create a Xerces DOM
parser
DOMParser parser = new DOMParser();
// parse the document
and
// access the root node with its children.
try {
parser.parse(xmlFile);
Document document = parser.getDocument();
NodeDetails(document);
} catch (SAXException e) {
// something went wrong!
} catch (IOException e) {
// something went wrong!
}
}
// recursively
traverse the document tree
private
void NodeDetails (Node node) {
try
{
int type = node.getNodeType();
if (type == Node.ELEMENT_NODE)
{
// if element
FormatTree(TabCounter);
out.write
("Element: " + node.getNodeName()
+ "<br>");
if(node.hasAttributes())
{
NamedNodeMap
AttributesList = node.getAttributes();
for(int j = 0; j < AttributesList.getLength();
j++) {
FormatTree(TabCounter);
out.write("Attribute:
" +
AttributesList.item(j).getNodeName()
+ " = " +
AttributesList.item(j).getNodeValue()
+ "<br>");
}
}
} else if (type == Node.TEXT_NODE)
{
//
if character data
Content = node.getNodeValue();
if (!Content.trim().equals("")){
FormatTree(TabCounter);
out.write ("Character Data: " + Content + "<br>");
}
} else if (type == Node.COMMENT_NODE) {
// if comment
Content = node.getNodeValue();
if (!Content.trim().equals("")){
FormatTree(TabCounter);
out.write("Comment:
" + Content + "<br>");
}
// add code for other node
types here if you like
}
NodeList children = node.getChildNodes();
if (children != null) {
for (int i=0; i< children.getLength();
i++) {
TabCounter++;
NodeDetails(children.item(i));
TabCounter--;
}
}
} catch (IOException
e) {
// something went wrong!
}
}
// this formats the output
as a tree
private void FormatTree (int TabCounter) {
try {
for(int
j = 1; j < TabCounter; j++) {
out.write(" ");
}
} catch (IOException e) {
// something went wrong!
}
}
}
The most important difference between this example and the previous one is the
introduction of a new Writer object, which makes it possible to redirect output
to the browser instead of the standard output device.
private Writer out;
The constructor also needs to be modified to accept two parameters: the name
of the XML file, and a reference to the Writer object.
// constructor
public MyFourthDomApp (String xmlFile, Writer out) {
// snip!
}
Note that, since I'm using a Writer object, I also need to add some code to trap
and resolve IOExceptions, if they occur. I've left that aside for a more detailed
discussion a little later - however, you should be aware of this requirement and
design your code appropriately.
You'll notice that I haven't made any major changes to the NodeDetails() function,
other than the inclusion of HTML tags in the output - this is what will ultimately
get sent to the browser. The only item left is to handle the connection between
the Java class above and the Web server - which is where JSP comes in.
Here's the JSP page that brings it all together:
<%@ page language="java" import="java.io.IOException" %>
<html>
<head>
</head>
<body>
<%
try {
MyFourthDomApp myFourthExample = new
MyFourthDomApp("/www/xerces/WEB-INF/classes/inventory.xml",out);
} catch (Exception e) {
out.println("Something bad happened!" + e);
}
%>
</body>
</html>
And here's what the output looks like:
For the moment, I'll ignore any errors that may occur when processing the JSP
page, deferring this to a later discussion.
