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4 Launching

This chapter introduces how to launch a Ratpack application, and the associated launch time configuration.

4.1 Launch configuration

To launch a Ratpack application, you must create a LaunchConfig. This can then be used with the RatpackServerBuilder method to create a RatpackServer that can then be started.

Note that one of the LaunchConfig object’s responsibilities is to provide a HandlerFactory implementation. This factory is responsible for creating the handler that is effectively the Ratpack application. See the chapter on handlers for more details.

One option for building a LaunchConfig is to use the LaunchConfigBuilder. Another option is to use LaunchConfigs which is able to build a launch config from system properties and a properties file.

4.2 RatpackMain

The RatpackMain class is a convenient entry point (i.e. main class) that bootstraps a Ratpack application. When building with Gradle, this is the default main class.

The minimum requirement for launching a RatpackMain based application, is to ensure there is a ratpack.properties file on the JVM classpath that indicates the application HandlerFactory

handlerFactory=org.my.HandlerFactory

All aspects of the LaunchConfig can be specified in this properties file. Aspects can also be environmentally overridden by JVM system properties. See RatpackMain for details.