struts的属性配置文件。默认为default.properties,已包含在struts2的发布包里面。
如果要修改配置文件，只需要在web application的classpath中放置一个struts.properties（一般放置在/WEB-INF/classes目录下）文件，并将需要修改的key和值写入该文件即可。

在开发环境下，需要配置的几个属性：
» struts.i18n.reload = true – enables reloading of internationalization files
» struts.devMode = true – enables development mode that provides more comprehensive debugging
» struts.configuration.xml.reload = true – enables reloading of XML configuration files (for the action)
          when a change is made without reloading the entire web application in the servlet container
» struts.url.http.port = 8080 – sets the port that the server is run on (so that generated URLs are created correctly)