action向jsp中传参数(报java.lang.NullPointerException错误)

Struts Problem Report

Struts has detected an unhandled exception:

Messages: File:org/apache/catalina/connector/Request.javaLine number:1,568

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Stacktraces

java.lang.NullPointerException

    org.apache.catalina.connector.Request.notifyAttributeAssigned(Request.java:1568)    org.apache.catalina.connector.Request.setAttribute(Request.java:1559)    org.apache.catalina.connector.RequestFacade.setAttribute(RequestFacade.java:541)    javax.servlet.ServletRequestWrapper.setAttribute(ServletRequestWrapper.java:239)    cn.itcast.elec.web.action.ElecMenuAction.alermZD(ElecMenuAction.java:77)    sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)    sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)    sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)    java.lang.reflect.Method.invoke(Method.java:606)    com.opensymphony.xwork2.DefaultActionInvocation.invokeAction(DefaultActionInvocation.java:441)    com.opensymphony.xwork2.DefaultActionInvocation.invokeActionOnly(DefaultActionInvocation.java:280)    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:243)    com.opensymphony.xwork2.interceptor.DefaultWorkflowInterceptor.doIntercept(DefaultWorkflowInterceptor.java:165)    com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:87)    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)    com.opensymphony.xwork2.validator.ValidationInterceptor.doIntercept(ValidationInterceptor.java:252)    org.apache.struts2.interceptor.validation.AnnotationValidationInterceptor.doIntercept(AnnotationValidationInterceptor.java:68)    com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:87)    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)    com.opensymphony.xwork2.interceptor.ConversionErrorInterceptor.intercept(ConversionErrorInterceptor.java:122)    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)    com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:195)    com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:87)    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)    com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:195)    com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:87)    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)    com.opensymphony.xwork2.interceptor.StaticParametersInterceptor.intercept(StaticParametersInterceptor.java:179)    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)    org.apache.struts2.interceptor.MultiselectInterceptor.intercept(MultiselectInterceptor.java:75)    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)    org.apache.struts2.interceptor.CheckboxInterceptor.intercept(CheckboxInterceptor.java:94)    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)    org.apache.struts2.interceptor.FileUploadInterceptor.intercept(FileUploadInterceptor.java:235)    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)    com.opensymphony.xwork2.interceptor.ModelDrivenInterceptor.intercept(ModelDrivenInterceptor.java:89)    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)    com.opensymphony.xwork2.interceptor.ScopedModelDrivenInterceptor.intercept(ScopedModelDrivenInterceptor.java:130)    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)    org.apache.struts2.interceptor.debugging.DebuggingInterceptor.intercept(DebuggingInterceptor.java:267)    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)    com.opensymphony.xwork2.interceptor.ChainingInterceptor.intercept(ChainingInterceptor.java:126)    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)    com.opensymphony.xwork2.interceptor.PrepareInterceptor.doIntercept(PrepareInterceptor.java:138)    com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:87)    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)    com.opensymphony.xwork2.interceptor.I18nInterceptor.intercept(I18nInterceptor.java:165)    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)    org.apache.struts2.interceptor.ServletConfigInterceptor.intercept(ServletConfigInterceptor.java:164)    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)    com.opensymphony.xwork2.interceptor.AliasInterceptor.intercept(AliasInterceptor.java:179)    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)    com.opensymphony.xwork2.interceptor.ExceptionMappingInterceptor.intercept(ExceptionMappingInterceptor.java:176)    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)    org.apache.struts2.impl.StrutsActionProxy.execute(StrutsActionProxy.java:52)    org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:488)    org.apache.struts2.dispatcher.ng.ExecuteOperations.executeAction(ExecuteOperations.java:77)    org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.doFilter(StrutsPrepareAndExecuteFilter.java:91)    org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)    org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)    org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:218)    org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122)    org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:505)    org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:169)    org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)    org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:956)    org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)    org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:442)    org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1083)    org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:640)    org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:318)    java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)    java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)    org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)    java.lang.Thread.run(Thread.java:744)    

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You are seeing this page because development mode is enabled. Development mode, or devMode, enables extra debugging behaviors and reports to assist developers. To disable this mode, set:

  struts.devMode=false

in your WEB-INF/classes/struts.propertiesfile.

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开始在action类中用

request.setAttribute("commonZDList",list);

向jsp页面(jsp页面采用s标签的方式取值)中传值，结果报错空指针异常。

----------------------------------------------------------------------------我是分隔符-------------------------------------------------------------------------

解决方法：

public String alermZD() {

List<ElecCommonMsgForm>list=elecCommonMsgService.findElecCommonMsgByCurrentDate();

ActionContext context=ActionContext.getContext();

HttpServletRequestrequest=(HttpServletRequest)context.get(ServletActionContext.HTTP_REQUEST);

request.setAttribute("commonZDList",list);

//context.put("commonZDList", list);

return"alermZD";

}

request的获取通过action上下文，而不让类实现ServletRequestAware接口

----------------------------------------------------------------------------我是分隔符-------------------------------------------------------------------------

补充：Struts2将ActionContext设置为OGNL上下文，并将值栈(Value Stack Contents)作为OGNL的根对象放置到ActionContext中。访问值栈中的对象不用“#”。Struts2总是把当前Action实例放置在栈顶。所以在OGNL中引用Action中的属性也可以省略“#”。

         调用ActionContext的put(key,value)放入的数据实际放入的是栈的上下文(Stack Context)中，需要使用#访问。

• 访问OGNL上下文和Action上下文，相当于ActionContext.getContext()；下表有几个ActionContext中有用的属性：

• 名称

  作用

  例子

  parameters

  包含当前HTTP请求参数的Map

  #parameters.id[0]作用相当于request.getParameter("id")

  request

  包含当前HttpServletRequest的属性（attribute)的Map

  #request.userName相当于request.getAttribute("userName")

  session

  包含当前HttpSession的属性（attribute）的Map

  #session.userName相当于session.getAttribute("userName")

  application

  包含当前应用的ServletContext的属性（attribute）的Map

  #application.userName相当于application.getAttribute("userName")

  attr

  用于按request >session > application顺序访问其属性（attribute）

  #attr.userName相当于按顺序在以上三个范围（scope）内读取userName属性，直到找到为止