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The first include element tells the framework to load the struts-default.xml, which it wil will find in the struts2.jar file. The struts-default.xml file defines the "standard" interceptor and result definitions.
You can put your own <include> elements in your struts.xml interchangeably with <package> elements. They The configuration objects will be loaded in the order of appearance. The framework reads the configuration from top to bottom and adds objects as they are referenced.@see com.opensymphony.xwork.config.ConfigurationManager
@see com.opensymphony.xwork.config.Configuration
@see com.opensymphony.xwork.config.impl.DefaultConfiguration
@see com.opensymphony.xwork.config.ConfigurationProvider
@see com.opensymphony.xwork.config.providers.XmlConfigurationProvider
By JAR
A "module" can be added to an application by placing a struts.xml and related classes into a JAR on the classpath. FreeMarker and Velocity templates can also be provided by JAR, making it possible to distribution a module in a single, self-contained JAR that is automatically configured on startup.