Tomcat 实现了Java Servlet规范,Java Servlet Pages技术,不同版本的Tomcat支持不同的Servlet及JSP规范.

• 最新示例图如下所示 :
  

不同版本的web.xml写法如下 :

• web.xml v2.3

  <?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>

• web.xml v2.4

  <?xml version="1.0" encoding="UTF-8"?>  
  <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>

• web.xml v2.5

  <?xml version="1.0" encoding="UTF-8"?>  
  <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>

• web.xml 3.0

  <?xml version="1.0" encoding="UTF-8"?>  
  <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">  
  </web-app>

• web.xml 4.0

  <?xml version="1.0" encoding="UTF-8"?> 
  <!DOCTYPE xml>
  <web-app  
          version="4.0"
          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_4_0.xsd">
  </web-app>