刚把上周说的公司内各工程的web.xml给统一了，顺便看了下每个tomcat版本对应的标准servlet版本，如下：

The XSD version is preferred since JSP 2.0 / Servlets 2.4 (eg: Tomcat 5.5). Note that the XML encoding can be specified as ISO-8859-1, UTF-8, or any other valid encoding in either version, and should match the actual encoding of your text file.

注意 servlet 2.4、3.1之后xsi的变化。

Servlet 3.1 deployment descriptor

<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">
</web-app>

XSD example for JSP 2.2 / Servlets 3.0 (Tomcat 7.0):

<?xml version="1.0" encoding="ISO-8859-1"?>
<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_3_0.xsd"
      version="3.0">

</web-app>

XSD example for JSP 2.1 / Servlets 2.5 (Tomcat 6.0):

<?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/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
     version="2.5">

</web-app>

XSD example for JSP 2.0 / Servlets 2.4 (Tomcat 5.5):

<?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 http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd"
     version="2.4">

</web-app>

DTD example for JSP 1.2 / Servlets 2.3 (Tomcat 5):

<?xml version="1.0" encoding="ISO-8859-1"?> 
<!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>

</web-app> 

官方参考可见http://www.oracle.com/webfolder/technetwork/jsc/xml/ns/javaee/index.html。

对于spring，对应关系如下：

• 4.0 最低要求JDK 6，支持websocket, Servlet 3.0+
• 3.0 最低要求JDK 1.5，基于注解的配置，servlet 2.4，完全支持REST，包从spring.jar拆分为按模块进行组织
• 2.5 最低要求JDK 1.4.2，Servlet 2.3, JSP 1.2

tomcat 5.5、6、7各版本的web-app标准