TemplateEngine seems to be fully-initialized when TemplateEngine.process() is called. I don't know what happens for the TemplateEngine initialization behind the scene, but TemplateEngine.initialize() is not allowed to be called directly, so I triggered it via TemplateEngine.getConfiguration(). It seems to provide an initialized state but it doesn't seem to be fully-initialized. I could trigger the fully-initialized state via invoking TemplateEngine.process() with a dummy template, but It would be nice if it could be achieved with an option.

TemplateEngineTimingTests.test() (Default) gives the following numbers:

Elapsed time: 672 // first request to template 1
Elapsed time: 2 // first request to template 2

TemplateEngineInitializeTimingTests.test() (Invoked TemplateEngine.getConfiguration() in advance) gives the following numbers:

Elapsed time: 196 // first request to template 1
Elapsed time: 1 // first request to template 2

TemplateEngineDummyInitTimingTests.test() (Invoked TemplateEngine.process() with a dummy template in advance) gives the following numbers:

Elapsed time: 706 // first request to a dummy template
Elapsed time: 8 // first request to template 1
Elapsed time: 2 // first request to template 2

The above mentioned tests are here: https://github.com/izeye/samples-java-branches/tree/master/src/test/java/learningtest/org/thymeleaf