struts的屬性配置文件。默認為default.properties,已包含在struts2的發布包里面。
如果要修改配置文件，只需要在web application的classpath中放置一個struts.properties（一般放置在/WEB-INF/classes目錄下）文件，并將需要修改的key和值寫入該文件即可。

在開發環境下，需要配置的幾個屬性：
? 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)