我是新手，正在学习Java，根据教材写的代码总是报错，请大家帮帮忙
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE struts-config PUBLIC "-//Apache Software Foundation//DTD Struts Configuration 1.2//EN" "http://struts.apache.org/dtds/struts-config_1_2.dtd">

<struts-config>
  <data-sources />
  <form-beans>
  <form-bean name="managerForm" type="document.ManagerForm"></form-bean>
  </form-beans>
  <global-exceptions />
  <global-forwards />
  <action-mappings>
  <action path="/manager" name="managerForm" type="document.ManagerAction">
  <forward name="managerLoginok" path="/main.jsp" />
  <forward name="error" path="/error.jsp" />
  </action>
  </action-mappings>
  <message-resources parameter="document.ApplicationResources" />
</struts-config>
《-------------------------报错------------------------------------》
三月 26, 2014 2:56:36 下午 org.apache.struts.util.RequestUtils createActionForm
严重: Error creating form bean of class document.ManagerForm
java.lang.NullPointerException
at org.apache.struts.config.FormBeanConfig.createActionForm(FormBeanConfig.java:212)
at org.apache.struts.util.RequestUtils.createActionForm(RequestUtils.java:292)
at org.apache.struts.util.RequestUtils.createActionForm(RequestUtils.java:191)
at org.apache.struts.action.RequestProcessor.processActionForm(RequestProcessor.java:331)
at org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:202)
at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1196)
at org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:432)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:646)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:220)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:501)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:170)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:98)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:950)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1040)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:607)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:313)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:744)
三月 26, 2014 2:56:36 下午 org.apache.struts.action.RequestProcessor processActionCreate
严重: No action instance for path /manager could be created
java.lang.ClassNotFoundException: document.ManagerAction
at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1718)
at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1569)
at org.apache.struts.util.RequestUtils.applicationClass(RequestUtils.java:117)
at org.apache.struts.util.RequestUtils.applicationInstance(RequestUtils.java:143)
at org.apache.struts.action.RequestProcessor.processActionCreate(RequestProcessor.java:292)
at org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:230)
at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1196)
at org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:432)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:646)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:220)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:501)