从数据库接收数据时收到空指针异常

我有我的数据库中存储的事件列表，但是当我尝试检索它们时，我得到的是一个胖空指针异常，即使结果存在。从数据库接收数据时收到空指针异常

这里是事件我的服务类

@Transactional 
public class EventServices { 
    // So Spring can inject the session factory 
    SessionFactory sessionFactory; 
    public void setSessionFactory(SessionFactory value) { 
     sessionFactory = value; 
    } 

    // Shortcut for sessionFactory.getCurrentSession() 
    public Session sess() { 
     return sessionFactory.getCurrentSession(); 
    } 

    @SuppressWarnings("unchecked") 
    public List<Event> getEvents() { 
     return sess().createQuery("from Event").list(); 
    } 
}

这里是我的ActionSupport类

public class EventAction extends ActionSupport { 

    protected EventServices eventServices; 

    protected String redirectUrl; 

    public String getRedirectUrl() { 
     return redirectUrl; 
    } 

    public void setRedirectUrl(String redirectUrl) { 
     this.redirectUrl = redirectUrl; 
    } 

    public void setEventServices(EventServices eventServices) { 
     this.eventServices = eventServices; 
    } 
}

我的事件动作类（Listing.java）

public class Listing extends EventAction{ 
    public String execute(){ 
     events = eventServices.getEvents(); 
     return "success"; 
    } 

    List<Event> events; 

    public List<Event> getEvents(){ return events; } 
}

从片段视图（Listing.jsp）

<s:iterator value="events"> 
    <form action='Delete.action'> 
    <input type='hidden' name=id value='<s:property value="id" />' /> 
    <input type='submit' value='-' title='Delete' /> 
    </form> 
    <form action='Attendance.action'> 
    <input type='hidden' name=id value='<s:property value="id" />' /> 
    <input type='submit' value='A' title='Attendance' /> 
    </form> 
    <s:property value="name" /> 
    <br> 
</s:iterator>

而且我不知道这是否会帮助，这是我的支柱配置XML

<?xml version="1.0" encoding="UTF-8" ?> 
<!DOCTYPE struts PUBLIC 
    "-//Apache Software Foundation//DTD Struts Configuration 2.0//EN" 
    "http://struts.apache.org/dtds/struts-2.0.dtd"> 

<struts> 
    <constant name="struts.devMode" value="true" /> <!-- set to false for prod --> 

    <package name="events" namespace="/events" extends="struts-default"> 
     <action name="*" class="actions.events.{1}"> 
      <result>/views/events/{1}.jsp</result> 
      <result name="redirect" type="redirect">${redirectUrl}</result> 
     </action> 
    </package> 

    <package name="root-redirect" namespace="/" extends="struts-default"> 
     <action name="*"> 
      <result type = "redirect">events/Listing.action</result> 
     </action> 
    </package> 

</struts>

而且应用程序上下文XML管理SessionFactory的

<?xml version="1.0" encoding="UTF-8"?> 
<beans xmlns="http://www.springframework.org/schema/beans" 
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:aop="http://www.springframework.org/schema/aop" 
    xmlns:tx="http://www.springframework.org/schema/tx" 
    xsi:schemaLocation=" 
     http://www.springframework.org/schema/beans 
     http://www.springframework.org/schema/beans/spring-beans-3.0.xsd 
     http://www.springframework.org/schema/tx 
     http://www.springframework.org/schema/tx/spring-tx-3.0.xsd 
     http://www.springframework.org/schema/aop 
     http://www.springframework.org/schema/aop/spring-aop-3.0.xsd"> 


    <bean id="sessionFactory" scope="singleton" 
     class="org.springframework.orm.hibernate4.LocalSessionFactoryBean"> 
     <property name="configLocation" value="classpath:hibernate.cfg.xml"/> 
    </bean> 

    <!-- Springs Hibernate Transaction Manager --> 
    <bean id ="transactionManager" class = "org.springframework.orm.hibernate4.HibernateTransactionManager"> 
     <property name = "sessionFactory" ref = "sessionFactory"/> 
    </bean> 

    <tx:annotation-driven/> 

    <!-- Inject my business services class to the action --> 
    <bean id="services" class ="services.Services" scope ="singleton"> 
     <property name = "sessionFactory" ref = "sessionFactory"/> 
    </bean> 

    <bean id="evemtservices" class ="services.EventServices" scope ="singleton"> 
     <property name = "sessionFactory" ref = "sessionFactory"/> 
    </bean> 

</beans>

的生命周期，这是错误

Struts Problem Report 
Struts has detected an unhandled exception: 
Messages: 
File: actions/events/Listing.java 
Line number: 12

完整的堆栈跟踪

根据意见10

java.lang.NullPointerException 
    actions.events.Listing.execute(Listing.java:13) 
    sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) 
    sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) 
    sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) 
    java.lang.reflect.Method.invoke(Unknown Source) 
    com.opensymphony.xwork2.DefaultActionInvocation.invokeAction(DefaultActionInvocation.java:446) 
    com.opensymphony.xwork2.DefaultActionInvocation.invokeActionOnly(DefaultActionInvocation.java:285) 
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248) 
    org.apache.struts2.interceptor.debugging.DebuggingInterceptor.intercept(DebuggingInterceptor.java:256) 
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:242) 
    com.opensymphony.xwork2.interceptor.DefaultWorkflowInterceptor.doIntercept(DefaultWorkflowInterceptor.java:176) 
    com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98) 
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:242) 
    com.opensymphony.xwork2.validator.ValidationInterceptor.doIntercept(ValidationInterceptor.java:265) 
    org.apache.struts2.interceptor.validation.AnnotationValidationInterceptor.doIntercept(AnnotationValidationInterceptor.java:68) 
    com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98) 
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:242) 
    com.opensymphony.xwork2.interceptor.ConversionErrorInterceptor.intercept(ConversionErrorInterceptor.java:138) 
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:242) 
    com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:238) 
    com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98) 
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:242) 
    com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:238) 
    com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98) 
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:242) 
    com.opensymphony.xwork2.interceptor.StaticParametersInterceptor.intercept(StaticParametersInterceptor.java:191) 
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:242) 
    org.apache.struts2.interceptor.MultiselectInterceptor.intercept(MultiselectInterceptor.java:75) 
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:242) 
    org.apache.struts2.interceptor.CheckboxInterceptor.intercept(CheckboxInterceptor.java:90) 
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:242) 
    org.apache.struts2.interceptor.FileUploadInterceptor.intercept(FileUploadInterceptor.java:252) 
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:242) 
    com.opensymphony.xwork2.interceptor.ModelDrivenInterceptor.intercept(ModelDrivenInterceptor.java:100) 
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:242) 
    com.opensymphony.xwork2.interceptor.ScopedModelDrivenInterceptor.intercept(ScopedModelDrivenInterceptor.java:141) 
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:242) 
    com.opensymphony.xwork2.interceptor.ChainingInterceptor.intercept(ChainingInterceptor.java:145) 
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:242) 
    com.opensymphony.xwork2.interceptor.PrepareInterceptor.doIntercept(PrepareInterceptor.java:171) 
    com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98) 
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:242) 
    com.opensymphony.xwork2.interceptor.I18nInterceptor.intercept(I18nInterceptor.java:176) 
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:242) 
    org.apache.struts2.interceptor.ServletConfigInterceptor.intercept(ServletConfigInterceptor.java:164) 
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:242) 
    com.opensymphony.xwork2.interceptor.AliasInterceptor.intercept(AliasInterceptor.java:193) 
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:242) 
    com.opensymphony.xwork2.interceptor.ExceptionMappingInterceptor.intercept(ExceptionMappingInterceptor.java:187) 
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:242) 
    org.apache.struts2.impl.StrutsActionProxy.execute(StrutsActionProxy.java:54) 
    org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:544) 
    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:243) 
    org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210) 
    com.opensymphony.sitemesh.webapp.SiteMeshFilter.obtainContent(SiteMeshFilter.java:129) 
    com.opensymphony.sitemesh.webapp.SiteMeshFilter.doFilter(SiteMeshFilter.java:77) 
    org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243) 
    org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210) 
    org.springframework.orm.hibernate4.support.OpenSessionInViewFilter.doFilterInternal(OpenSessionInViewFilter.java:119) 
    org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:76) 
    org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243) 
    org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210) 
    org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:225) 
    org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:169) 
    org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472) 
    org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:168) 
    org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:98) 
    org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:927) 
    org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118) 
    org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407) 
    org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:999) 
    org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:565) 
    org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:309) 
    java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) 
    java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) 
    java.lang.Thread.run(Unknown Source)

来源

2012-12-03 KyelJmD

你能显示完整的错误堆栈吗？看起来好像服务没有被注入到你的动作中，以及你如何在你的动作类中注入'eventServices'，因为有一个错字为'eventServices'，id是'evemtservices' –

@UmeshAwasthi我发布了完整的堆栈跟踪重新检查问题 – KyelJmD

你有没有交叉验证错字？你已经将它声明为'evemtservices'，而它在你的action类中被命名为'eventservices'？ –

发布答案：

问题是基于错字上春节无法在OP的作用class.In bean定义

<bean id="evemtservices" class ="services.EventServices" scope ="singleton"> 
     <property name = "sessionFactory" ref = "sessionFactory"/> 
</bean>

标识被宣布为注射服务evemtservices，而在行动类中使用的财产被命名为eventservices。

由于没有服务被Spring注入，因此方法调用正在抛出空指针。

来源

2012-12-03 04:58:01

你能在这里提供更多解释吗？因为我不能在applicationContext.xml中使用eventServices或EventAction，Spring是如何发现eventServices变量的？ – KyelJmD

我相信你正在使用struts2-spring插件，请参阅插件doc以找出正在注入的依赖项http://struts.apache.org/2.3.4/docs/spring-plugin.html –

从数据库接收数据时收到空指针异常

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