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There are two frameworks that do the template rendering in Confluence: Webwork and Sitemesh. The confusing bit is that both of them use Velocity as their templating engine. We try to distinguish them by using *.vm for templates processed by Webwork, and *.vmd for those processed by Sitemesh.
There are four different Velocity contexts used in Confluence:
templates processed by Webwork use the context defined in ConfluenceVelocityContext
templates processed by Sitemesh as a result of the #applyDecorator() directive use the context defined in ApplyDecoratorDirective
templates processed by Sitemesh as a result of the URL mapping in decorators.xml use the context defined in ProfilingPageFilter
templates processed by the notification queue use the context defined in VelocityRenderedQueueItem.
The two Sitemesh contexts are pretty much the same, but the Webwork velocity context contains a lot more stuff than either of the Sitemesh ones.
The following diagram shows the logical structure of the Confluence UI.
Confluence UI Architecture - Logical Structure
The following diagram shows the flow of control through the Confluence UI.
Confluence UI Architecture - Execution Flow
In more detail, the flow of control goes:
Webwork gets request, maps request URL to action using xwork.xml
Webwork maps response of action to a Velocity template using xwork.xml
Webwork launches Velocity handler on template (*.vm) with context defined in ConfluenceVelocityContext
Velocity process content in *.vm file
Within an #applyDecorator() directive:
Velocity calls the ApplyDecoratorDirective class with the parameters and body content of the directive
Any #decoratorParam() directives are processed by the ParamDirective class, which pushes bits of the current Velocity context into the ApplyDecoratorDirective parameters
ApplyDecoratorDirective matches the name parameter of the directive with a *.vmd file from decorators.xml
ApplyDecoratorDirective launches Sitemesh on a decorator template (*.vmd) with context defined in ApplyDecoratorDirective
Sitemesh returns decorated content
Velocity template finished processing rest of *.vm file, returns to Webwork
Web.xml servlet filter 'sitemesh' maps to ProfilingPageFilter, a Sitemesh page filter
Sitemesh uses the request URL mapping in decorators.xml to launch a decorator template (*.vmd) with context defined in ProfilingPageFilter
Sitemesh returns decorated content as response.
You can find out which beans are in which context by looking in the classes above. A full list would be too long to include here. Note that even though the ApplyDecoratorDirective launches a Sitemesh decorator template, the Sitemesh template doesn't get automatic access to the Velocity context. The only bits that are passed through are done with the #decoratorParam() directive.
Wow, pretty complicated. But it lets us do cool stuff like implement custom themes, apply layouts and more.