web版本问题

访问http://xmlns.jcp.org/xml/ns/javaee/可下载各版本的约束文档，文档中有对应版本的约束格式web-app 2.3<!DOCTYPE web-app PUBLIC  "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN" "http://java.sun.com/dtd/web-app_2_3.dtd" >web-app 2.4<web-app id="WebApp_9" version="2.4" 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 http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd"> web-app 2.5<web-app xmlns="http://java.sun.com/xml/ns/javaee"  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"  xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"  version="2.5"> jdk版本1.5以上web-app 3.0<web-app          version="3.0"          xmlns="http://java.sun.com/xml/ns/javaee"          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"          xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"> jdk版本1.6以上,开始支持jsp-config配置web-app 3.1<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"      xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"      version="3.1">   jdk版本1.7以上