Saturday, December 15, 2007

Jakarta VelocityJakarta Velocity
Apache Velocity is an open source package directed by the Apache Software Foundation. Velocity is a Java-based template engine that provides a simple yet powerful template language to reference objects defined in Java code. Its aim is to ensure clean separation between the presentation tier and business tiers in a Web application (see model-view-controller design pattern). Some common types of applications which use Velocity are:

Web applications: Web designers create HTML pages with placeholders for dynamic information. The page is processed with VelocityViewServlet or any of a number of frameworks which support Velocity. This approach to web application development is called Model-view-controller (MVC), and is intended to be a direct replacement for applications developed with JSP or PHP.
Source code generation: Velocity can be used to generate Java source code, SQL, or PostScript, based on templates. The PoweredByVelocity page lists a number of open source, and commercial development software packages which use Velocity in this manner.
Automatic emails: Many applications generate automatic emails for account signup, password reminders, or automatically sent reports. Using Velocity, the email template can be stored in a text file, rather than directly embedded in Java code.
XML transformation: Velocity provides an ant task, called Anakia, which reads an XML file and makes it available to a Velocity template. A common application is to convert documentation stored in a generic "xdoc" format into a styled HTML document. Code Example
The following template:
processed by Velocity will produce the following text:
The syntax and overall concept of the Apache Velocity templates is very similar to the syntax of the older WebMacro template engine which is now also an open source project.

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