Home arrow XML arrow Page 2 - XML Parsing With DOM and Xerces (part 2)

The Writing On The Wall - XML

In this concluding article of a two-part series, use your knowledge of DOM processing with Xerces to construct simple Web applications based on Xerces, XML and JSP. Examples include transforming an XML file to HTML via Xerces and dynamically generating an XML document tree from a MySQL database.

TABLE OF CONTENTS:
  1. XML Parsing With DOM and Xerces (part 2)
  2. The Writing On The Wall
  3. Highlights
  4. Data Overload
  5. Oops!
  6. Dear Diary
  7. Of Method And Madness
  8. Black Or White
  9. Link Out
By: icarus, (c) Melonfire
Rating: starstarstarstarstar / 9
March 06, 2002

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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("&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"); } } 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.

 
 
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