今天在练习Servlet的时候 在web.xml下配置了多个Servlet程序的信息，配置的Servlet都没错，但是web.xml的第一行却显示了个错误。
The errors below were detected when validating the file “web-app_2_5.xsd” via the file “web.xml”. In most cases these errors can be detected by validating “web-app_2_5.xsd” directly. However it is possible that errors will only occur when web-app_2_5.xsd is validated in the context of web.xml.
查看了一下，大概是说web 2.5的标准支头信息引用的JDK的工作空间不匹配，下面修改之
将
http://java.sun.com/xml/ns/j2ee/web-app_2_5.xsd
修改为
http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd
解决了 
参考：
http://*.com/questions/4816330/web-app-2-5-xsd-showing-errors-when-validating-web-xml-in-eclipse