The content of element type "web-app" must match "(icon?,display-

错误：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.

注意顺序：<servlet>,<servlet-mapping>需要分开写，先写所有的servlet，后写servlet-mapping