[报错]Attribute "xmlns:xsi" must be declared for element type "web-app"

Multiple annotations found at this line:

- Attribute “version” must be declared for element type “web-app”.

- Attribute “xsi:schemaLocation” must be declared for element type “web-app”.

- 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*)”.

- Attribute “xmlns:xsi” must be declared for element type “web-app”.

- Attribute “xmlns” must be declared for element type “web-app”.

webapp这个标签必须是第一行的，前面有注释文档都不可以，所以将webapp这个标签前面的文档全部删掉就可以了