Article Author: Nazmul Idris
Date: March 27 1999.
Copyright Nazmul Idris 1998-2006. All Rights Reserved. 

About the tool
Before you begin
What should you use it for?
Limitations
How was it built?
License
Downloading the source code and running the program

DomView is a program that allows you to learn how to use the DOM 1.0 API. It does so by displaying XML documents as a tree of nodes and then displaying the DOM interfaces that each node implements; it also invokes methods that are available for each interface and displays the output of these methods. This tool is great for learning what exactly a DOM object tree is and how it can be used to extract or process information in your XML documents. It is also useful for seeing the differences in the DOM API implementation in different XML parsers.

Here is a screen shot of the program:

Currently DomView supports the Sun, IBM and OpenXML parsers, but it can quickly be made to work with any Java XML parser (that implements the DOM 1.0 API) by adding two or three lines of code. The source code (and documentation) is included as usual :). In fact, DomView 1.0 comes with a GNU Public License so that anyone is free to make it better and give it away to other developers. 

The parser versions that are needed are:

• Sun Project X Technology Release 1 
• IBM XML Parser for Java v2.0.4 
• OpenXML v1.0.4. 

You can download these parsers from the tool section.

While you are reading the tutorial and trying out the examples, please use the links in the references section to understand terms that you are unfamiliar with. We are assuming that you are familiar with XML (and all its related terminology) before you start using this tool.

DomView is a teaching tool that will help you learn the DOM API by showing you what the DOM API does. This tool is built around the DOM 1.0 interfaces and it can simply be used to show you what your XML documents look like through DOM (rather than SAX for example).

DomView also shows you all the interfaces implemented by each node object in the DOM document tree. This information is available in the W3C's documentation of DOM, but actually seeing it before your eyes makes it easier to understand and remember. There is no guesswork involved, the tool shows everything as it is.

The tool can also be used to see how different XML parsers implement DOM. Remember, the W3C Recommendation for XML 1.0 and DOM 1.0 are just that, a recommendation. It is not a specification and the W3C hopes that most companies will stick to the recommendation, but vendors are free to implement things any way they want. DomView can be used to test DOM 1.0 compliance, since it is designed to work only with the DOM 1.0 interfaces. So if you are evaluating a new parser, DomView will show you what parts of DOM 1.0 are implemented by the parser. It does not do any performance testing, but you can download some performance testing code from here.

DomView only uses the accessor methods available in all the DOM interfaces, not the mutator methods. We are writing another tool called DomEdit which will overcome this limitation. This tool is a generic XML editor which we will release in the next week (also with a GPL), so stay tuned :).

DomView uses the W3C DOM API interfaces that are available with any Java XML Parser distribution. We created a Swing TreeModel that "sits" on top of a Document object (that is created by the XML Parser implementation). This document object's class is unimportant, because it is parser dependent. The important thing is that this object can be accessed using the DOM API interfaces. This is exactly what the TreeModel does. The root of the custom TreeModel is this document object (created by the parser). The TreeModel's methods turn around and call their DOM counterparts to manipulate the document object. This also saves memory, since the document object does not have to copied into another object model (like it was done in Tutorial2 (Swing, Servlet). 

All we did was provide another interface layer on top of DOM to allow the Swing JTree to access the actual document object created by the XML Parser (containing information from your XML document). Java interfaces are very powerful and time saving. Since Swing uses Model View Controller (MVC), you can conceivably wrap the complex Swing model interfaces on top of DOM in order to view your document object using different UI components.

Please study to the source code (that can be downloaded at the end of this article) to see how the TreeModel interface was actually implemented on top of the DOM API. Once you study the source code everything becomes quite clear. It is not that difficult or complicated to do this because the TreeModel and DOM interfaces are both designed to work with hierarchical information. Now, if we trying to wrap a TableModel around any document object, that might require a lot more work. If you are wondering if this can be done, it can. By using some sort of TreeTableModel interface (and corresponding TreeTable UI component) you can achieve this.

This software is released with GNU Public License (GPL) so that anyone can modify it to their hearts content as long as they distribute their work with the GPL also.

You need to download the IBM, Sun and OpenXML parsers before using DomView. You can download these parsers from the tools section. Before running the program please refer to How-to: Setup CLASSPATH article for information on how to setup your CLASSPATH on JDK1.1 and 1.2 so that you can use these parsers.

Here is the distribution zip file (containing source code, documentation and notes) for DomView: src.zip.

The table below contains a description of the folders and files in the zip file for the software distribution. Please note that you MUST have all 3 parsers (Sun, IBM and OpenXML) setup on your system before you can run this program. 

To run the DomView, first download the src.zip file and unzip it to a folder of your choice.  From this folder, you can type "java DomView" at the command prompt. Make sure that you have Java2 (or JDK1.2) installed on your machine because it will not work with JDK1.1. Also make sure that the Sun, IBM and OpenXML parser jar files are in the classpath of the JVM. If you want to know how to do this, click here.

Once DomView starts, three JFrames will appear on your desktop. The title of the frames indicates which XML parser is being used by it. The first thing to do is choose a JFrame with the parser you want to test and choose the "File -> Open" menu. You must then type in the complete path to an XML document accessible locally (e.g.: "c:\domview\birds.xml"). An XML file called "birds.xml" is provided with the software distribution. You can use any XML document that you have. Please note that if you are using XML documents with external DTDs, then you must setup you document so that it refers to the external DTD by using a fully qualified path name to the DTD file. If you are not using a DTD, or using internal DTDs, then you don't have to concern yourself with this.

Please go to the tools section to actually download the Parsers themselves.

I hope you enjoy DomView.