java - 通过 Spring 注入(inject)使用 Query 进行 hibernate

Question

初学者在这里 hibernate ， Spring 。按照这里的教程设置hibernae + spring + struts2项目:
http://splinter.com.au/blog/?p=224

我想准备查询。所以我尝试了以下操作:
服务.java

public class Services {
  protected SessionFactory sessionFactory;
  public void setSessionFactory(SessionFactory value) {
    sessionFactory = value;
  }

  protected Session sess() {
    return sessionFactory.getCurrentSession();
  }

  private Query query = sess().createQuery("....");
}

由于未注入(inject) session 而引发以下异常，我该如何解决？

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'services' defined in ServletContext resource [/WEB-INF/applicationContext.xml]: Instantiation of bean failed; nested exception is org.springframework.beans.BeanInstantiationException: Could not instantiate bean class [com.dao.Services]: Constructor threw exception; nested exception is java.lang.NullPointerException
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateBean(AbstractAutowireCapableBeanFactory.java:955)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:901)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:485)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:456)
    at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:291)
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222)
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:288)
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:190)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:574)
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:895)
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:425)
    at org.springframework.web.context.ContextLoader.createWebApplicationContext(ContextLoader.java:276)
    at org.springframework.web.context.ContextLoader.initWebApplicationContext(ContextLoader.java:197)
    at org.springframework.web.context.ContextLoaderListener.contextInitialized(ContextLoaderListener.java:47)
    at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:3910)
    at org.apache.catalina.core.StandardContext.start(StandardContext.java:4393)
    at org.jboss.web.tomcat.service.deployers.TomcatDeployment.performDeployInternal(TomcatDeployment.java:310)
    at org.jboss.web.tomcat.service.deployers.TomcatDeployment.performDeploy(TomcatDeployment.java:142)
    at org.jboss.web.deployers.AbstractWarDeployment.start(AbstractWarDeployment.java:461)
    at org.jboss.web.deployers.WebModule.startModule(WebModule.java:118)
    at org.jboss.web.deployers.WebModule.start(WebModule.java:97)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at org.jboss.mx.interceptor.ReflectedDispatcher.invoke(ReflectedDispatcher.java:157)
    at org.jboss.mx.server.Invocation.dispatch(Invocation.java:96)
    at org.jboss.mx.server.Invocation.invoke(Invocation.java:88)
    at org.jboss.mx.server.AbstractMBeanInvoker.invoke(AbstractMBeanInvoker.java:264)
    at org.jboss.mx.server.MBeanServerImpl.invoke(MBeanServerImpl.java:668)
    at org.jboss.system.microcontainer.ServiceProxy.invoke(ServiceProxy.java:206)
    at $Proxy38.start(Unknown Source)
    at org.jboss.system.microcontainer.StartStopLifecycleAction.installAction(StartStopLifecycleAction.java:42)
    at org.jboss.system.microcontainer.StartStopLifecycleAction.installAction(StartStopLifecycleAction.java:37)
    at org.jboss.dependency.plugins.action.SimpleControllerContextAction.simpleInstallAction(SimpleControllerContextAction.java:62)
    at org.jboss.dependency.plugins.action.AccessControllerContextAction.install(AccessControllerContextAction.java:71)
    at org.jboss.dependency.plugins.AbstractControllerContextActions.install(AbstractControllerContextActions.java:51)
    at org.jboss.dependency.plugins.AbstractControllerContext.install(AbstractControllerContext.java:348)
    at org.jboss.system.microcontainer.ServiceControllerContext.install(ServiceControllerContext.java:297)
    at org.jboss.dependency.plugins.AbstractController.install(AbstractController.java:1633)
    at org.jboss.dependency.plugins.AbstractController.incrementState(AbstractController.java:935)
    at org.jboss.dependency.plugins.AbstractController.resolveContexts(AbstractController.java:1083)
    at org.jboss.dependency.plugins.AbstractController.resolveContexts(AbstractController.java:985)
    at org.jboss.dependency.plugins.AbstractController.change(AbstractController.java:823)
    at org.jboss.dependency.plugins.AbstractController.change(AbstractController.java:553)
    at org.jboss.system.ServiceController.doChange(ServiceController.java:688)
    at org.jboss.system.ServiceController.start(ServiceController.java:460)
    at org.jboss.system.deployers.ServiceDeployer.start(ServiceDeployer.java:163)
    at org.jboss.system.deployers.ServiceDeployer.deploy(ServiceDeployer.java:99)
    at org.jboss.system.deployers.ServiceDeployer.deploy(ServiceDeployer.java:46)
    at org.jboss.deployers.spi.deployer.helpers.AbstractSimpleRealDeployer.internalDeploy(AbstractSimpleRealDeployer.java:62)
    at org.jboss.deployers.spi.deployer.helpers.AbstractRealDeployer.deploy(AbstractRealDeployer.java:50)
    at org.jboss.deployers.plugins.deployers.DeployerWrapper.deploy(DeployerWrapper.java:171)
    at org.jboss.deployers.plugins.deployers.DeployersImpl.doDeploy(DeployersImpl.java:1440)
    at org.jboss.deployers.plugins.deployers.DeployersImpl.doInstallParentFirst(DeployersImpl.java:1158)
    at org.jboss.deployers.plugins.deployers.DeployersImpl.doInstallParentFirst(DeployersImpl.java:1179)
    at org.jboss.deployers.plugins.deployers.DeployersImpl.install(DeployersImpl.java:1099)
    at org.jboss.dependency.plugins.AbstractControllerContext.install(AbstractControllerContext.java:348)
    at org.jboss.dependency.plugins.AbstractController.install(AbstractController.java:1633)
    at org.jboss.dependency.plugins.AbstractController.incrementState(AbstractController.java:935)
    at org.jboss.dependency.plugins.AbstractController.resolveContexts(AbstractController.java:1083)
    at org.jboss.dependency.plugins.AbstractController.resolveContexts(AbstractController.java:985)
    at org.jboss.dependency.plugins.AbstractController.change(AbstractController.java:823)
    at org.jboss.dependency.plugins.AbstractController.change(AbstractController.java:553)
    at org.jboss.deployers.plugins.deployers.DeployersImpl.process(DeployersImpl.java:782)
    at org.jboss.deployers.plugins.main.MainDeployerImpl.process(MainDeployerImpl.java:702)
    at org.jboss.system.server.profileservice.repository.MainDeployerAdapter.process(MainDeployerAdapter.java:117)
    at org.jboss.system.server.profileservice.repository.ProfileDeployAction.install(ProfileDeployAction.java:70)
    at org.jboss.system.server.profileservice.repository.AbstractProfileAction.install(AbstractProfileAction.java:53)
    at org.jboss.system.server.profileservice.repository.AbstractProfileService.install(AbstractProfileService.java:403)
    at org.jboss.dependency.plugins.AbstractControllerContext.install(AbstractControllerContext.java:348)
    at org.jboss.dependency.plugins.AbstractController.install(AbstractController.java:1633)
    at org.jboss.dependency.plugins.AbstractController.incrementState(AbstractController.java:935)
    at org.jboss.dependency.plugins.AbstractController.resolveContexts(AbstractController.java:1083)
    at org.jboss.dependency.plugins.AbstractController.resolveContexts(AbstractController.java:985)
    at org.jboss.dependency.plugins.AbstractController.install(AbstractController.java:775)
    at org.jboss.dependency.plugins.AbstractController.install(AbstractController.java:540)
    at org.jboss.system.server.profileservice.repository.AbstractProfileService.registerProfile(AbstractProfileService.java:308)
    at org.jboss.system.server.profileservice.ProfileServiceBootstrap.start(ProfileServiceBootstrap.java:256)
    at org.jboss.bootstrap.AbstractServerImpl.start(AbstractServerImpl.java:461)
    at org.jboss.Main.boot(Main.java:221)
    at org.jboss.Main$1.run(Main.java:556)
    at java.lang.Thread.run(Unknown Source)
Caused by: org.springframework.beans.BeanInstantiationException: Could not instantiate bean class [com.dao.Services]: Constructor threw exception; nested exception is java.lang.NullPointerException
    at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:141)
    at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:71)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateBean(AbstractAutowireCapableBeanFactory.java:948)
    ... 82 more
Caused by: java.lang.NullPointerException
    at com.dao.Services.sess(Services.java:36)
    at com.dao.Services.<init>(Services.java:42)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
    at java.lang.reflect.Constructor.newInstance(Unknown Source)
    at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:126)
    ... 84 more

Answer 1

当一个 Service被实例化，query字段被初始化。而此时，sessionFactory尚未注入(inject)，因此 NullPointerException .

但实际上，初始化 Query 的整个想法在 Service创建时间没有多大意义，因为查询绑定(bind)到 session 的生命周期。来自 Query 的 javadoc :

Queries are executed by calling list(), scroll() or iterate(). A query may be re-executed by subsequent invocations. Its lifespan is, however, bounded by the lifespan of the Session that created it.

换句话说，您应该创建一个 Query每次通话，而不是一劳永逸:

public class Services {
    protected SessionFactory sessionFactory;
    public void setSessionFactory(SessionFactory value) {
        sessionFactory = value;
    }

    public List foo() {
       Query query = sessionFactory.getCurrentSession().createQuery("....");
       ...
    }
}