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|File:Jakarta Velocity Logo.png|
|Developer(s)||Apache Software Foundation|
|Stable release||1.6.2 / March 19, 2009|
|Operating system||Cross platform|
|License||Apache License 2.0|
Apache Velocity (formerly known as Jakarta Velocity) is an open source software project 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.
The following template:
## Velocity Hello World <html> <body> #set( $foo = "Velocity" ) ## followed by Hello $foo World! </body> </html>
processed by Velocity will produce the following text:
<html> <body> Hello Velocity World! </body> </html>
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.
- Harrop, Rob; Darwin, Ian (August 30, 2004), Pro Jakarta Velocity: From Professional to Expert (1st ed.), Apress, pp. 370, ISBN 978-1590594100, http://www.apress.com/book/view/9781590594100
- Cole, Jim; D. Gradecki, Joseph (July 16, 2003), Mastering Apache Velocity (1st ed.), Wiley, pp. 372, ISBN 978-0471457947, http://www.wiley.com/WileyCDA/WileyTitle/productCd-0471457949.html