|
Deliver On-the-Fly Mapping Services to Your Rich Desktop Java Application, Part 2
by Dan Andrews
Part 1 of this series highlighted the explosion of interest in online mapping services, also touching upon some of the mathematics used by many of the mapping services. Specifically, you learned how to use the quadkey and x, y, z notation to request individual tiles from a tile server.
Part 2 covers how to stay current with the inevitable explosion of free mapping services without recompiling your client's Java code. You'll do this by creating an XML description of how to access a tile server.
First, you'll create an XML schema definition (XSD), which will be a flexible representation of how to access a tile server. Your XSD will also capture some metadata about the tile server—things like its name and a tooltip that would be suitable for a menu item. Next, you'll write an Open Street Map XML data implementation conforming to your XSD. You'll also learn how to parse your XML using the Simple API for XML (SAX). You'll generate a tile URL dynamically using Mozilla's JavaScript for Java (Rhino).
Along the way, code exerts will hopefully illustrate key concepts. Click here to download the complete code for this article as an Eclipse project.
TileFactories XSD
An XSD is always a good starting point before planning any XML data implementation. An XSD communicates the required XML structure in a way that allows programs and programmers to agree.
Your XSD defines a root element named TileFactories, which implies that it will describe information for accessing one or more tile servers. The compete XSD is shown in Listing 1. The choice of the "Factory" metaphor in this XSD will become more evident in Part 3, where you'll use the SwingX-WS project to build a rich client mapping application.
As you can see, Listing 1 begins with some metadata to describe the name, description, and author of the eventual XML data implementation. The IsProduction element describes whether or not the XML will be intended for production code.
A sequence of one or more FactoryInfo elements is used to describe what you need to know about the physical attributes of tiles and the tile server. These attributes include tile size and available zoom levels. The BuildURLFunction element will be used for a JavaScript function that will return a URL to a single map tile.
The FactoryInfo metadata includes a name and tooltip for menu items. Optional metadata includes credit information, terms, and additional copyright information. Except for the AddCopyright element, the other metadata elements do not need further explanation.
The AddCopyright element can be used to show additional copyright information or credits for particular areas of a map. Zoom in on Tampa Bay, Florida, with Google Maps using the satellite map type to see how this works. At a zoom level of 13 or greater, the copyright notice in Google Maps satellite map type in this area contains "The Florida Department of Environmental Protection." The additional copyright information will be used to model this behavior, should it be required, in your rich Java application. Now that you've got your XSD written, you can write your XML implementation.
New on the Java Boutique:
New Review:
Time Management Made Easy with the Quartz Enterprise Job Scheduler
Why not just use the Java timer API? This open source scheduling
API boasts simplicity, ease-of-integration, a well-rounded feature
set, and it's free!
New Applet:
Reverse Complement
Reverse Complement is a simple applet that converts DNA or RNA
sequences into three useful formats.
Elsewhere on internet.com:
WebDeveloper Java
Lots of Java information on webdeveloper.com
WDVL Java
Thorough Java resource at the Web Developer's Virtual Library.
ScriptSearch Java
Hundreds of free Java code files to download.
jGuru: Your View of the Java Universe
Customizable portal with online training, FAQs, regular news updates, and tutorials.
| 
