关于Servlet的问题？帮忙看一下？

500 Servlet Exception
WEB-INF/web.xml:9: <description> is an unexpected tag (parent <web-app>
starts at 6). Check for duplicate and out-of-order tags.
<web-app> syntax: (@id?, @version, @xsi:schemaLocation,
(<context-param>*
& (<description>*, <display-name>?, <icon>?)
& <distributable>?
& (<env-entry>*, <ejb-ref>*, <ejb-local-ref>*, <service-ref>*, <resource-ref>*, <resource-env-ref>*, <message-destination-ref>*)
& <error-page>*
& <filter>*
& <filter-mapping>*
& <jsp-config>?
& <listener>*
& <locale-encoding-mapping-list>?
& <login-config>?
& <message-destination>*
& <mime-mapping>*
& <security-constraint>*
& <security-role>*
& <servlet>*
& <servlet-mapping>*
& <session-config>?
& <welcome-file-list>?))

————————————————————————————————————————
我的web.xml配置是 ：：：<?xml version="1.0" encoding="ISO-8859-1"?>

<web-app xmlns="http://java.sun.com/xml/ns/j2ee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee web-app_2_4.xsd"
version="2.4">

<display-name>Welcome to Resin</display-name>
<description>
JSP应用开发详解
</description>
<servlet>
<servlet-name>HelloWorldServlet</servlet-name>
<servlet-class>HelloWorldServlet</servlet-class>
</servlet>

<servlet-mapping>
<servlet-name>HelloWorldServlet</servlet-name>
<url-pattern>/hello</url-pattern>

</servlet-mapping>
</web-app>


帮我看看是什么问题