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Server-Side Java: Using XML and JSP together

Two great tastes that taste great together

By Alex Chaffee, JavaWorld.com, 03/02/00

Page 2 of 3

In this case, as in most low-to-medium volume, publishing-based Websites, you can assume the following: most of the data access is reads, not writes; the data, though potentially large, is relatively unchanging; you won't need to do complicated searches, but if you do, you'll use a separate search engine. The advantages of using a mature RDBMS fade, while the advantage of using an object-oriented data model come to the fore.

Finally, it's entirely possible to provide a wrapper for your database that makes SQL queries and translates them into XML streams, so you could have it both ways. XML becomes a more robust, programmer-friendly frontend to a mature database for storing and searching. (Oracle's XSQL servlet is one example of this technique.)

The application: An online photo album

Everybody loves photos! People love showing pictures of themselves, their friends, their pets, and their vacations. The Web is the ultimate medium for self-indulgent shutterbugs -- they can annoy their relatives from thousands of miles away. While a full-fledged photo album site would require a complicated object model, I'll focus on defining a single Picture object. (The source code for this application is available in Resources.) The object representing a picture needs fields representing its title, the date it was taken, an optional caption, and, obviously, a pointer to the image source.

An image, in turn, needs a few fields of its own: the location of the source file (a GIF or JPEG) and the height and width in pixels (to assist you in building <img> tags). Here there is one neat advantage to using the filesystem as your database: you can store the image files in the same directory as the data files.

Finally, let's extend the picture record with an element defining a set of thumbnail images for use in the table of contents or elsewhere. Here I use the same concept of image I defined earlier.

The XML representation of a picture could look something like this:

<picture>
  <title>Alex On The Beach</title>
  <date>1999-08-08</date>
  <caption>Trying in vain to get a tan</caption>
  <image>
    <src>alex-beach.jpg</src>
    <width>340</width>
    <height>200</height>
  </image>
  <thumbnails>
    <image>
      <src>alex-beach-sm.jpg</src>
      <width>72</width>
      <height>72</height>
    </image>
    <image>
      <src>alex-beach-med.jpg</src>
      <width>150</width>
      <height>99</height>
    </image>
  </thumbnails>
</picture>

Note that by using XML, you put all the information about a single picture into a single file, rather than scattering it among three or four separate tables. Let's call this a .pix file -- so your filesystem might look like this:

 summer99/alex-beach.pix
 summer99/alex-beach.jpg
 summer99/alex-beach-sm.jpg
 summer99/alex-beach-med.jpg
 summer99/alex-snorkeling.pix
 etc.

Techniques

There's more than one way to skin a cat, and there's more than one way to bring XML data on to your JSP page. Here is a list of some of those ways. (This list is not exhaustive; many other products and frameworks would serve equally well.)

• DOM: You can use classes implementing the DOM interface to parse and inspect the XML file
• XMLEntryList: You can use my code to load the XML into a java.util.List of name-value pairs
• XPath: You can use an XPath processor (like Resin) to locate elements in the XML file by path name
• XSL: You can use an XSL processor to transform the XML into HTML
• Cocoon: You can use the open source Cocoon framework
• Roll your own bean: You can write a wrapper class that uses one of the other techniques to load the data into a custom JavaBean

Note that these techniques could be applied equally well to an XML stream you receive from another source, such as a client or an application server.