请把问题说具体些，我刚测试过，是可以运行的。

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5" 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">
    <servlet>
        <servlet-name>UpLoad</servlet-name>
        <servlet-class>com.wgh.servlet.UpLoad</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>UpLoad</servlet-name>
        <url-pattern>/UpLoad</url-pattern>
    </servlet-mapping>
      <servlet>
    <servlet-name>ProgressBarServlet</servlet-name>
    <servlet-class>com.wgh.sevlet.ProgressBarServlet</servlet-class>
  </servlet>
    <servlet-mapping>
        <servlet-name>ProgressBarServlet</servlet-name>
        <url-pattern>/ProgressBarServlet</url-pattern>
    </servlet-mapping>  
    <session-config>
        <session-timeout>
            30
        </session-timeout>
    </session-config>
    <filter>
        <filter-name>CharacterEncodingFilter</filter-name>
        <filter-class>com.wgh.filter.CharacterEncodingFilter</filter-class>
        <init-param>
            <param-name>encoding</param-name>
            <param-value>UTF-8</param-value>
        </init-param>
    </filter>
    <filter-mapping>
        <filter-name>CharacterEncodingFilter</filter-name>
        <url-pattern>/*</url-pattern>
        <dispatcher>REQUEST</dispatcher>
        <dispatcher>FORWARD</dispatcher>
    </filter-mapping>
    <welcome-file-list>
        <welcome-file>index.jsp</welcome-file>
    </welcome-file-list>
    </web-app>


里面有ProgressBarServlet 但是我的源文件中找不到，，程序根本跑不起来。。
本来买这本书就是冲着Ajax来的。。想学些知识，，，看看实例，现在没办法跑起来啊。。。。

请问您是用NetBeans集成开发工具运行的吗？

您好，下面的代码在本实例中没有用到，请您将下面的代码删除，保存后再运行试一下。
<servlet>
<servlet-name>ProgressBarServlet</servlet-name>
<servlet-class>com.wgh.sevlet.ProgressBarServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>ProgressBarServlet</servlet-name>
<url-pattern>/ProgressBarServlet</url-pattern>
</servlet-mapping>