關於web.xml不同版本之間的區別

一、Servlet 2.3 

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<!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>
  <display-name>Servlet 2.3 Web Application</display-name>
</web-app>

二、Servlet 2.4

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<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>
  <display-name>Servlet 2.4 Web Application</display-name>
</web-app>

三、Servlet 2.5 

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<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">
<web-app>
  <display-name>Servlet 2.5 Web Application</display-name>
</web-app>

四、Servlet 3.0

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<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>
  <display-name>Servlet 3.0 Web Application</display-name>
</web-app>

參考於：http://www.mkyong.com/web-development/the-web-xml-deployment-descriptor-examples/

http://en.wikipedia.org/wiki/Java_Servlet