添加hibernate多对多配置后启动tomcat报错

今天，在新增了PrivilegeEntity(权限)和其对应的hibernate配置文件之后，在其配置文件中配置了对应的对于RoleEntity(角色)的多对多关系之后，启动Tomcat之后报了如下错误：

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'com.zhi.service.impl.MenuServiceImpl': Injection of resource dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'com.zhi.dao.impl.MenuDAOImpl' defined in file [D:\Program Files\Apache Software Foundation\Tomcat 7.0\webapps\CRM\WEB-INF\classes\com\crm\dao\impl\MenuDAOImpl.class]: Initialization of bean failed; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'sessionFactory' defined in file [D:\Program Files\Apache Software Foundation\Tomcat 7.0\webapps\CRM\WEB-INF\classes\beans.xml]: Invocation of init method failed; nested exception is java.lang.NullPointerException
at org.springframework.context.annotation.CommonAnnotationBeanPostProcessor.postProcessPropertyValues(CommonAnnotationBeanPostProcessor.java:300)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1074)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:517)
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.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:1075)
at org.directwebremoting.spring.SpringCreator.getInstance(SpringCreator.java:144)
at org.directwebremoting.spring.SpringCreator.getType(SpringCreator.java:106)
at org.directwebremoting.impl.DefaultCreatorManager.addCreator(DefaultCreatorManager.java:118)
at org.directwebremoting.impl.DefaultCreatorManager.addCreator(DefaultCreatorManager.java:100)
at org.directwebremoting.impl.DwrXmlConfigurator.loadCreate(DwrXmlConfigurator.java:274)
at org.directwebremoting.impl.DwrXmlConfigurator.loadAllows(DwrXmlConfigurator.java:224)
at org.directwebremoting.impl.DwrXmlConfigurator.configure(DwrXmlConfigurator.java:170)
at org.directwebremoting.impl.ContainerUtil.configureFromDefaultDwrXml(ContainerUtil.java:262)
at org.directwebremoting.impl.ContainerUtil.configureContainerFully(ContainerUtil.java:419)
at org.directwebremoting.servlet.DwrServlet.init(DwrServlet.java:79)
at org.apache.catalina.core.StandardWrapper.initServlet(StandardWrapper.java:1266)
at org.apache.catalina.core.StandardWrapper.loadServlet(StandardWrapper.java:1185)
at org.apache.catalina.core.StandardWrapper.load(StandardWrapper.java:1080)
at org.apache.catalina.core.StandardContext.loadOnStartup(StandardContext.java:5001)
at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5289)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
at org.apache.catalina.startup.HostConfig.checkResources(HostConfig.java:1362)
at org.apache.catalina.startup.HostConfig.check(HostConfig.java:1450)
at org.apache.catalina.startup.HostConfig.lifecycleEvent(HostConfig.java:295)
at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:119)
at org.apache.catalina.util.LifecycleBase.fireLifecycleEvent(LifecycleBase.java:90)
at org.apache.catalina.core.ContainerBase.backgroundProcess(ContainerBase.java:1338)
at org.apache.catalina.core.ContainerBase$ContainerBackgroundProcessor.processChildren(ContainerBase.java:1496)
at org.apache.catalina.core.ContainerBase$ContainerBackgroundProcessor.processChildren(ContainerBase.java:1506)
at org.apache.catalina.core.ContainerBase$ContainerBackgroundProcessor.run(ContainerBase.java:1485)
at java.lang.Thread.run(Thread.java:722)
Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'com.zhi.dao.impl.MenuDAOImpl' defined in file [D:\Program Files\Apache Software Foundation\Tomcat 7.0\webapps\CRM\WEB-INF\classes\com\crm\dao\impl\MenuDAOImpl.class]: Initialization of bean failed; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'sessionFactory' defined in file [D:\Program Files\Apache Software Foundation\Tomcat 7.0\webapps\CRM\WEB-INF\classes\beans.xml]: Invocation of init method failed; nested exception is java.lang.NullPointerException
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:527)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:456)
at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:291)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:288)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:194)
at org.springframework.context.annotation.CommonAnnotationBeanPostProcessor.autowireResource(CommonAnnotationBeanPostProcessor.java:435)
at org.springframework.context.annotation.CommonAnnotationBeanPostProcessor.getResource(CommonAnnotationBeanPostProcessor.java:409)
at org.springframework.context.annotation.CommonAnnotationBeanPostProcessor$ResourceElement.getResourceToInject(CommonAnnotationBeanPostProcessor.java:541)
at org.springframework.beans.factory.annotation.InjectionMetadata$InjectedElement.inject(InjectionMetadata.java:147)
at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:84)
at org.springframework.context.annotation.CommonAnnotationBeanPostProcessor.postProcessPropertyValues(CommonAnnotationBeanPostProcessor.java:297)
... 34 more
Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'sessionFactory' defined in file [D:\Program Files\Apache Software Foundation\Tomcat 7.0\webapps\CRM\WEB-INF\classes\beans.xml]: Invocation of init method failed; nested exception is java.lang.NullPointerException
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1420)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:519)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:456)
at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:291)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:288)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:190)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.autowireByName(AbstractAutowireCapableBeanFactory.java:1104)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1054)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:517)
... 45 more
Caused by: java.lang.NullPointerException
at org.hibernate.mapping.Table$ForeignKeyKey.equals(Table.java:96)
at java.util.HashMap.get(HashMap.java:322)
at org.hibernate.mapping.Table.createForeignKey(Table.java:592)
at org.hibernate.mapping.Table.createForeignKey(Table.java:585)
at org.hibernate.mapping.SimpleValue.createForeignKeyOfEntity(SimpleValue.java:128)
at org.hibernate.mapping.Collection.createForeignKeys(Collection.java:418)
at org.hibernate.mapping.Collection.createAllKeys(Collection.java:426)
at org.hibernate.cfg.CollectionSecondPass.doSecondPass(CollectionSecondPass.java:66)
at org.hibernate.cfg.Configuration.originalSecondPassCompile(Configuration.java:1716)
at org.hibernate.cfg.Configuration.secondPassCompile(Configuration.java:1423)
at org.hibernate.cfg.Configuration.buildMappings(Configuration.java:1375)
at org.springframework.orm.hibernate3.LocalSessionFactoryBean.buildSessionFactory(LocalSessionFactoryBean.java:717)
at org.springframework.orm.hibernate3.AbstractSessionFactoryBean.afterPropertiesSet(AbstractSessionFactoryBean.java:211)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1477)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1417)
... 54 more

纳闷了半天，之前Menu相关的配置都没有错误，今天修改也没有碰MenuEntity的配置文件啊，怎么会出现注入失败的错误呢，最后耐下心来看了一下错误，在错误的错误信息我们可以看到

Caused by: java.lang.NullPointerException
at org.hibernate.mapping.Table$ForeignKeyKey.equals(Table.java:96)
at java.util.HashMap.get(HashMap.java:322)

这个错误，错误显示的是外键的错误，所以我回过头去看配置文件，然后发现真的是PrivilegeEntity.hbm.xml的多对多配置出错，我写成了如下形式：

<set name="roleSet" lazy="false" cascade="all" table="role_privilege">
<key column="privilegeId" />
<many-to-many column="roleId" />
</set>

，发现是忘了配置class=“”，他找不到对应的类，所以出错，应该配成 class="RoleEntity" 。下次要小心一点了

总结：看错误信息一般是最后的错误信息才是最有用的，前面说的什么注入失败都是由后面引起的，不要受其影响，在这上面纠结，找错误