Tutorials : Java and JDOM: the perfect couple :

A web application to handle the DVD library

In the final example I'll show you how to build a simple web application to manage a list of DVDs held in an XML file. We'll need two screens: one for showing the list of DVDs and one screen to show the details for a single DVD. On these screens we can then implement the basic operations "Save list of DVDs", "Create DVD", "Update DVD", and "Delete DVD". First the DVD list screen:

By clicking on the "Id"-hyperlinks you'll go to this screen:

I have used a very simple MVC-architecture for these two screens, using only jsp-files:

All the four files share a JavaBean called DVDManager. It contains the create, update and delete methods described above, a method to build the document tree, and several getters used by the List and Details screens.

You enter the application from the List controller, giving the command "file" and the name of the file that contains the DVD information. For example:

http://localhost:8080/dvds/ctllist.jsp?command=file&name=d:\dvds.xml

The List page uses the getter-methods to display the DVDs. By clicking on the Id-hyperlink you invoke the controller to the Details page, giving it the DVD's index in the List of DVDs. The details page again uses the getters to show the DVD data. Clicking on any of the buttons of the page brings you back to the controller for the List page. The controller will always sort the DVDs according to their titles.

All the four pages can be found in the zip-file whose address is given in the Resources section below.

Outputting the XML-tree

The XML document may be written in XML-format to an OutputStream or a Writer. You use the XMLOutputter class for this. In the beginning of the article you saw how to write the document to System.out:

XMLOutputter output = new XMLOutputter();
output.output(doc, System.out); 

Writing to a named file is just as simple:

FileWriter f = new FileWriter(new File("d:\\newfile.xml"));
outputter.output(doc, f);
f.close();

You can control the format of the listing by setting indentations and line breaks either with the XMLOutput constructor or by setter-methods.

JDOM has two other output possibilities. The document tree may be sent to a SAX event-receiver using the SAXOutputter class. Finally you may convert the JDOM tree into a DOM tree by the DOMOutputter class.

Conclusion

If you're a Java programmer (and you probably are if you've gotten this far!) you'll probably like JDOM. It builds on well-known Java language features, and hides much of the complexity in XML by making the common things simple to do. It's also important to notice that JDOM is a very open architecture that works well with other API's like SAX and DOM. If you're interested in how JDOM evolves and when it might become a standard, you can consider joining the mailing lists found at jdom.org.

Resources

• The code for all the examples in the article
• jdom.org -- home of JDOM -- news, downloads, documentation, FAQs and much more
• Easy Java/XML integration with JDOM -- a thorough walk-through of the most important features -- written by the founders of the JDOM project

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