你的servlet在web.xml文件中申明了吗?类似<servlet>
       <servlet-name>ChackServlet</servlet-name>
       <servlet-class>ChackServlet</servlet-class>
  </servlet>
   <servlet-mapping>
       <servlet-name>ChackServlet</servlet-name>
       <url-pattern>/chack_servlet<url-pattern>
   </servlet-mapping>