使用工具类在非spring容器管理的类中获取bean时报错

抛出异常

java.lang.NullPointerException
	at javabean.newcredit.creditreport.util.SpringContextUtil.getBean(SpringContextUtil.java:46)
	at javabean.newcredit.creditreport.service.serviceimpl.ProcessReportWorkFlowService.<init>(ProcessReportWorkFlowService.java:36)
	at javabean.newcredit.creditreport.service.serviceimpl.ExternalNetSellReportServiceImplT.<init>(ExternalNetSellReportServiceImplT.java:109)
	at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
	at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
	at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
	at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
	at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:171)
	at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:148)
	at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:52)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateBean(AbstractAutowireCapableBeanFactory.java:486)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:362)
	at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveInnerBeanDefinition(BeanDefinitionValueResolver.java:151)
	at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveValueIfNecessary(BeanDefinitionValueResolver.java:97)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyPropertyValues(AbstractAutowireCapableBeanFactory.java:1046)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:857)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:378)
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:233)
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:145)
	at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveReference(BeanDefinitionValueResolver.java:186)
	at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveValueIfNecessary(BeanDefinitionValueResolver.java:106)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyPropertyValues(AbstractAutowireCapableBeanFactory.java:1046)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:857)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:378)
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:233)
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:145)
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:283)
	at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:313)
	at org.springframework.web.context.support.AbstractRefreshableWebApplicationContext.refresh(AbstractRefreshableWebApplicationContext.java:139)
	at org.springframework.web.context.ContextLoader.createWebApplicationContext(ContextLoader.java:252)
	at org.springframework.web.context.ContextLoader.initWebApplicationContext(ContextLoader.java:190)
	at org.springframework.web.context.ContextLoaderListener.contextInitialized(ContextLoaderListener.java:49)
	at weblogic.servlet.internal.EventsManager$FireContextListenerAction.run(EventsManager.java:481)
	at weblogic.security.acl.internal.AuthenticatedSubject.doAs(AuthenticatedSubject.java:321)
	at weblogic.security.service.SecurityManager.runAs(SecurityManager.java:120)
	at weblogic.servlet.internal.EventsManager.notifyContextCreatedEvent(EventsManager.java:181)
	at weblogic.servlet.internal.WebAppServletContext.preloadResources(WebAppServletContext.java:1868)
	at weblogic.servlet.internal.WebAppServletContext.start(WebAppServletContext.java:3154)
	at weblogic.servlet.internal.WebAppModule.startContexts(WebAppModule.java:1518)
	at weblogic.servlet.internal.WebAppModule.start(WebAppModule.java:484)
	at weblogic.application.internal.flow.ModuleStateDriver$3.next(ModuleStateDriver.java:425)
	at weblogic.application.utils.StateMachineDriver.nextState(StateMachineDriver.java:52)
	at weblogic.application.internal.flow.ModuleStateDriver.start(ModuleStateDriver.java:119)
	at weblogic.application.internal.flow.ScopedModuleDriver.start(ScopedModuleDriver.java:200)
	at weblogic.application.internal.flow.ModuleListenerInvoker.start(ModuleListenerInvoker.java:247)
	at weblogic.application.internal.flow.ModuleStateDriver$3.next(ModuleStateDriver.java:425)
	at weblogic.application.utils.StateMachineDriver.nextState(StateMachineDriver.java:52)
	at weblogic.application.internal.flow.ModuleStateDriver.start(ModuleStateDriver.java:119)
	at weblogic.application.internal.flow.StartModulesFlow.activate(StartModulesFlow.java:27)
	at weblogic.application.internal.BaseDeployment$2.next(BaseDeployment.java:671)
	at weblogic.application.utils.StateMachineDriver.nextState(StateMachineDriver.java:52)
	at weblogic.application.internal.BaseDeployment.activate(BaseDeployment.java:212)
	at weblogic.application.internal.SingleModuleDeployment.activate(SingleModuleDeployment.java:44)
	at weblogic.application.internal.DeploymentStateChecker.activate(DeploymentStateChecker.java:161)
	at weblogic.deploy.internal.targetserver.AppContainerInvoker.activate(AppContainerInvoker.java:79)
	at weblogic.deploy.internal.targetserver.BasicDeployment.activate(BasicDeployment.java:184)
	at weblogic.deploy.internal.targetserver.BasicDeployment.activateFromServerLifecycle(BasicDeployment.java:361)
	at weblogic.management.deploy.internal.DeploymentAdapter$1.doActivate(DeploymentAdapter.java:51)
	at weblogic.management.deploy.internal.DeploymentAdapter.activate(DeploymentAdapter.java:200)
	at weblogic.management.deploy.internal.AppTransition$2.transitionApp(AppTransition.java:30)
	at weblogic.management.deploy.internal.ConfiguredDeployments.transitionApps(ConfiguredDeployments.java:240)
	at weblogic.management.deploy.internal.ConfiguredDeployments.activate(ConfiguredDeployments.java:169)
	at weblogic.management.deploy.internal.ConfiguredDeployments.deploy(ConfiguredDeployments.java:123)
	at weblogic.management.deploy.internal.DeploymentServerService.resume(DeploymentServerService.java:180)
	at weblogic.management.deploy.internal.DeploymentServerService.start(DeploymentServerService.java:96)
	at weblogic.t3.srvr.SubsystemRequest.run(SubsystemRequest.java:64)
	at weblogic.work.ExecuteThread.execute(ExecuteThread.java:256)
	at weblogic.work.ExecuteThread.run(ExecuteThread.java:221)

问题描述

在一个没有交给spring容器管理的service中使用容器管理的dao，dao在成员变量的位置用SpringContextUtil获取。

Dao dao  = (Dao)SpringContextUtil.getBean("Dao");

Ps：
该service通过new的方式新建；
SpringContextUtil是继承了ApplicationContextAware的工具类，用于获取工具类所在的spring容器。

报错原因

普通类和spring容器的加载顺序不同。
非容器管理的类在程序启动时先初始化，spring容器后加载。
此时在给类变量进行赋值的时候，getBean()取不到指定的bean，所以为空。

解决方法

将dao放在需要使用的方法内部进行getBean初始化，此时spring容器已经加载完毕，不会报错。