Velocity is a Java based template engine. It can be used as a stand-alone utility for generating source code, HTML, reports, or it can be combined with other systems to provide template services. One such example is the planned marriage of Velocity with the Turbine web application framework. Velocity will be tightly integrated with Turbine to provide a template service that will enable a true MVC model by which web applications may be developed.

The original concept for Velocity was borrowed from WebMacro. We are gratious for the amount of development and design work that went into WebMacro.

The fundamental design of Velocity is around the idea that there are a few useful script elements that you embed within your HTML code that work in conjunction with a Context object that is populated in your Java code. The purpose of the Context object is to provide a "hook" from your Java code to your Velocity code. Essentially a Context object is simply a Hashtable which provides get and set methods for retrieving and setting objects by name within the Context. These script elements provide enough basic functionality to allow you to retrieve objects from the Context and put them into your page as text values with some degree of control over looping (for each) and conditional statements (if/else).

For people who are not familiar with MVC style of development, at first glance, it will appear as though Velocity is missing a large set of functionality. It turns out that this is actually the strength of Velocity. For example, unlike JSP, there is no way to embed Java code within your page and the script elements provide little more than basic looping and conditional statements. Another example is the PHP model where every single feature is implemented with another function. So, how is this better than the alternatives? The answer is that by using Velocity, you are enforcing a MVC style of development which defines that your Java code and your HTML template code should be separate. This style of development sometimes takes slightly longer (especially if you are new to MVC), but results in much more maintainable code over the long term (believe us, we have been doing this for a long time now). It also provides an abstraction that prevents page designers from messing with software engineer's Java code. In other words, it provides an enforcement of a contract that defines what roles people play in the development process.