Swing Hacks

Add Velocity for Dynamic HTML #98

Chapter 12, Miscellany

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493

HACK

As an example, suppose you want to display the weather for the next three

days as part of your application. You need a nice graphic weather display

showing your users the current weather, as in Figure 12-13.

Velocity and Templates

Velocity is an open source template engine, released under the Apache

Jakarta umbrella. At its simplest, Velocity allows you to add intelligent

replacement from a text file. At its most extreme, Velocity allows you to call

Java methods and use the entire VTL (Velocity Template Language) to cre-

ate intelligent templates using loops, conditionals, and variables. In other

words, you get the power of an MVC infrastructure like JSP, but in a very

lightweight local-client technology.

When using Velocity, you have two basic elements to deal with: the

VelocityContext and the template. The VelocityContext holds objects that

can be referenced from the template. The template is text with imbedded

VTL that controls the Velocity output.

In this simple example,

${name} and ${what} indicate replaceable values:

${name} is a total ${what}

Here is a simple context:

VelocityContext context = new VelocityContext( );

context.put("name", Jonathan);

context.put("what", Rockstar);

Figure 12-13. A graphical weather page