解决The content of element type "web-app" must match报错

Spring MVC中配置多个Servlet时，IDEA报错，如下：

The content of element type "web-app" must match "(icon ,display-
name ,description ,distributable ,context-param*,filter*,filter-mapping*,listener*,servlet*,servlet-
mapping*,session-config ,mime-mapping*,welcome-file-list ,error-page*,taglib*,resource-env-
ref*,resource-ref*,security-constraint*,login-config ,security-role*,env-entry*,ejb-ref*,ejb-local-ref*)".
- No grammar constraints (DTD or XML schema) detected for the document.

意思很简单，次序不对，很多博文建议删除DOCTYPE中的校验代码方法是不推荐的。

正确做法是调整次序。

如web.xml中存在如下多个servlet，此时编辑器将报错，xml代码如下：

 1   <servlet>
 2     <servlet-name>UserServlet</servlet-name>
 3     <servlet-class>fun.liping.web.UserServlet</servlet-class>
 4   </servlet>
 5   <servlet-mapping>
 6     <servlet-name>UserServlet</servlet-name>
 7     <url-pattern>/userServlet</url-pattern>
 8   </servlet-mapping>
 9   <servlet>
10     <servlet-name>DispatcherServlet</servlet-name>
11     <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
12     <load-on-startup>1</load-on-startup>
13   </servlet>
14   <servlet-mapping>
15     <servlet-name>DispatcherServlet</servlet-name>
16     <url-pattern>/</url-pattern>
17   </servlet-mapping>

此时要保证所有的servlet标签在servlet-mapping标签前面，调整次序如下：

 1   <servlet>
 2     <servlet-name>UserServlet</servlet-name>
 3     <servlet-class>fun.liping.web.UserServlet</servlet-class>
 4   </servlet>
 5   <servlet>
 6     <servlet-name>DispatcherServlet</servlet-name>
 7     <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
 8     <load-on-startup>1</load-on-startup>
 9   </servlet>
10   <servlet-mapping>
11     <servlet-name>UserServlet</servlet-name>
12     <url-pattern>/userServlet</url-pattern>
13   </servlet-mapping>
14   <servlet-mapping>
15     <servlet-name>DispatcherServlet</servlet-name>
16     <url-pattern>/</url-pattern>
17   </servlet-mapping>