Apache 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:
## 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.
See Also
External links
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