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Template framework

The template framework in Groovy consists of a TemplateEngine abstract base class that engines must
implement and a Template interface that the resulting templates they generate must implement.

Included with Groovy is the SimpleTemplateEngine that allows you to use JSP-like scriptlets (see example below), script, and EL expressions in your template in order to generate parametrized text. Here is an example of using the system:

Though its possible to plug in any kind of template engine dialect, we can share the same API to invoke templates. e.g. we could create a Velocity / FreeMarker flavour TemplateEngine implemenation which could reuse GPath and auto-recompile to bytecode.

Using TemplateServlet to serve single JSP-like HTML files

Mind the gap! Ehm, meaning the difference between Groovlets and Templates.




just works the opposite as the Groovlets (


) does. Here, your source are HTML (or any other, fancy template files) and the template framework will generate a Groovy script on-the-fly. This script could be saved to a .groovy file and the served by GroovyServlet (and the GroovyScriptEngine), but after generation, the template is evaluated and responded to the client.

Here is a simple example helloworld.html file which is not validating and does not have an head element. But it demonstrates, how to let Groovy compile and serve your HTML files to web clients. The tag syntax close to JSP and should be easy to read:

The first Groovy block - a for loop - spans the HelloWorld! text. Guess what happens? And the second Groovy statement prints the servlet's session id - if there is a session avaiable. The variable session is one of some default bound keys. More details reveals the documentation of


Here is some sample code using http://jetty.mortbay.orgs servlet container. With jetty6.0, copy jetty-6.1.3.jar and jetty-util-6.1.3.jar into $HOME/.groovy/lib,  create a tiny web server with the following. To test it, add your above helloworld.html file into your current directory and browse http://localhost:1234/helloworld.html

Here is a similiar web.xml example.

Further reading

Article on templating with Groovy templates by Andrew Glover
Article on templating with Groovlets and TemplateServlets by Andrew Glover

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