Document root element "beans:beans", must match DOCTYPE root "null".

如果报错误：

严重: Exception sending context initialized event to listener instance of class org.springframework.web.context.ContextLoaderListener
org.springframework.beans.factory.BeanDefinitionStoreException: Line 13 in XML document from ServletContext resource [/WEB-INF/applicationContext-security-ns.xml] is invalid; nested exception is org.xml.sax.SAXParseException: Document root element "beans:beans", must match DOCTYPE root "null".
org.xml.sax.SAXParseException: Document root element "beans:beans", must match DOCTYPE root "null".

?

?

则应该去检查Spring jar 的版本，Spring1和2的命名空间的声明是不同的。

检查版本的方法是:

jar包里面的META-INF中的MANIFEST.MF文件中一般会记录版本信息。