web.xml中配置的servlet明明存在，却报ClassNotFound异常

最近在学习黄勇的《架构探险-从零开始写Java Web框架》，按照书上写了个smart-framework框架。在yoga项目测试该框架的时候，启动tomcat报异常。
java.lang.ClassNotFoundException: org.smart4j.smart_framework.DispatcherServlet
at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1269)
at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1104)
at org.apache.catalina.core.DefaultInstanceManager.loadClass(DefaultInstanceManager.java:508)
at org.apache.catalina.core.DefaultInstanceManager.loadClassMaybePrivileged(DefaultInstanceManager.java:489)
at org.apache.catalina.core.DefaultInstanceManager.newInstance(DefaultInstanceManager.java:119)
at org.apache.catalina.core.StandardWrapper.loadServlet(StandardWrapper.java:1041)
at org.apache.catalina.core.StandardWrapper.load(StandardWrapper.java:980)
at org.apache.catalina.core.StandardContext.loadOnStartup(StandardContext.java:4819)
at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5129)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:183)
at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1425)
at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1415)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at org.apache.tomcat.util.threads.InlineExecutorService.execute(InlineExecutorService.java:75)
at java.util.concurrent.AbstractExecutorService.submit(AbstractExecutorService.java:134)
at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:941)
at org.apache.catalina.core.StandardHost.startInternal(StandardHost.java:839)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:183)
at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1425)
at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1415)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at org.apache.tomcat.util.threads.InlineExecutorService.execute(InlineExecutorService.java:75)
at java.util.concurrent.AbstractExecutorService.submit(AbstractExecutorService.java:134)
at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:941)
at org.apache.catalina.core.StandardEngine.startInternal(StandardEngine.java:258)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:183)
at org.apache.catalina.core.StandardService.startInternal(StandardService.java:422)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:183)
at org.apache.catalina.core.StandardServer.startInternal(StandardServer.java:770)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:183)
at org.apache.catalina.startup.Catalina.start(Catalina.java:657)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:483)
at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:355)
at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:495)九月 24, 2017 10:54:50 上午 org.apache.coyote.AbstractProtocol start
信息: Starting ProtocolHandler ["http-nio-8080"]
九月 24, 2017 10:54:50 上午 org.apache.coyote.AbstractProtocol start
信息: Starting ProtocolHandler ["ajp-nio-8009"]
九月 24, 2017 10:54:50 上午 org.apache.catalina.startup.Catalina start
信息: Server startup in 880 ms
我在web.xml中配置了该servlet    org.smart4j.smart_framework.DispatcherServlet，点击该链接也能找到DispatcherServlet类。下边是web.xml配置
<web-app>
  <display-name>Archetype Created Web Application</display-name>
  <servlet>
   <servlet-name>dispatcherServlet</servlet-name>
   <servlet-class>org.smart4j.smart_framework.DispatcherServlet</servlet-class>
   <load-on-startup>1</load-on-startup>
  </servlet>
  <servlet-mapping>
   <servlet-name>dispatcherServlet</servlet-name>
   <url-pattern>/*</url-pattern>
  </servlet-mapping>
</web-app>下面是项目chapter3结构，里边有  org.smart4j.smart_framework.DispatcherServlet类