1、网上说了很多例子，这就不说了，只介绍下我遇见的问题
java.lang.ClassCastException: org.hibernate.ejb.HibernatePersistence cannot be cast to javax.persistence.spi.PersistenceProvider
这是启动jboss5的时候报错，问题出在jboss5 client中
javax.persistence_2.0.0.jar hibernate3.jar javassist-3.9.0.GA.jar
这3jar已经有了，然后在项目中加入这些jar后，就会出现如上错误。
如果要在tomcate下运行，必须加上上面几个jar文件，如果是在jboss中，则只要把jboss client中的jar作为classpath导入项目。
2、还有个问题，现在我依然没弄清楚为什么，
19:36:32,593 WARN [AbstractDeploymentContext] Unable to register deployment mbean org.jboss.metadata.jpa.spec.PersistenceUnitMetaData.pop
javax.management.InstanceAlreadyExistsException: jboss.deployment:id="org.jboss.metadata.jpa.spec.PersistenceUnitMetaData.pop",type=Componen
t already registered.
at org.jboss.mx.server.registry.BasicMBeanRegistry.add(BasicMBeanRegistry.java:756)
at org.jboss.mx.server.registry.BasicMBeanRegistry.registerMBean(BasicMBeanRegistry.java:233)
at sun.reflect.GeneratedMethodAccessor75.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.jboss.mx.interceptor.ReflectedDispatcher.invoke(ReflectedDispatcher.java:157)
at org.jboss.mx.server.Invocation.dispatch(Invocation.java:96)
at org.jboss.mx.interceptor.AbstractInterceptor.invoke(AbstractInterceptor.java:138)
at org.jboss.mx.server.Invocation.invoke(Invocation.java:90)
at org.jboss.mx.interceptor.ModelMBeanOperationInterceptor.invoke(ModelMBeanOperationInterceptor.java:140)
at org.jboss.mx.server.Invocation.invoke(Invocation.java:90)
at org.jboss.mx.server.AbstractMBeanInvoker.invoke(AbstractMBeanInvoker.java:264)
at org.jboss.mx.server.MBeanServerImpl.invoke(MBeanServerImpl.java:668)
at org.jboss.mx.server.MBeanServerImpl$3.run(MBeanServerImpl.java:1431)
at java.security.AccessController.doPrivileged(Native Method)
at org.jboss.mx.server.MBeanServerImpl.registerMBean(MBeanServerImpl.java:1426)
at org.jboss.mx.server.MBeanServerImpl.registerMBean(MBeanServerImpl.java:376)
at org.jboss.deployers.structure.spi.helpers.AbstractDeploymentContext.registerMBeans(AbstractDeploymentContext.java:1030)
at org.jboss.deployers.structure.spi.helpers.AbstractDeploymentContext.addComponent(AbstractDeploymentContext.java:722)
at org.jboss.deployers.structure.spi.helpers.AbstractDeploymentUnit.addComponent(AbstractDeploymentUnit.java:251)
at org.jboss.deployers.spi.deployer.helpers.ComponentAdapter.addComponent(ComponentAdapter.java:59)
at org.jboss.deployers.spi.deployer.helpers.AbstractDeploymentVisitor.deploy(AbstractDeploymentVisitor.java:73)
at org.jboss.deployers.spi.deployer.helpers.AbstractRealDeployerWithInput.deploy(AbstractRealDeployerWithInput.java:125)
at org.jboss.deployers.spi.deployer.helpers.AbstractRealDeployerWithInput.internalDeploy(AbstractRealDeployerWithInput.java:102)
at org.jboss.deployers.spi.deployer.helpers.AbstractComponentDeployer.internalDeploy(AbstractComponentDeployer.java:78)
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:1439)
at org.jboss.deployers.plugins.deployers.DeployersImpl.doInstallParentFirst(DeployersImpl.java:1157)
at org.jboss.deployers.plugins.deployers.DeployersImpl.install(DeployersImpl.java:1098)
at org.jboss.dependency.plugins.AbstractControllerContext.install(AbstractControllerContext.java:348)
at org.jboss.dependency.plugins.AbstractController.install(AbstractController.java:1631)
at org.jboss.dependency.plugins.AbstractController.incrementState(AbstractController.java:934)
at org.jboss.dependency.plugins.AbstractController.resolveContexts(AbstractController.java:1082)
at org.jboss.dependency.plugins.AbstractController.resolveContexts(AbstractController.java:984)
at org.jboss.dependency.plugins.AbstractController.change(AbstractController.java:822)
at org.jboss.dependency.plugins.AbstractController.change(AbstractController.java:553)
at org.jboss.deployers.plugins.deployers.DeployersImpl.process(DeployersImpl.java:781)
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.hotdeploy.HDScanner.scan(HDScanner.java:362)
at org.jboss.system.server.profileservice.hotdeploy.HDScanner.run(HDScanner.java:255)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:441)
at java.util.concurrent.FutureTask$Sync.innerRunAndReset(FutureTask.java:317)
at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:150)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$101(ScheduledThreadPoolExecutor.java:98)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.runPeriodic(ScheduledThreadPoolExecutor.java:181)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:205)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
at java.lang.Thread.run(Thread.java:619)
19:36:32,593 WARN [AbstractDeploymentContext] Unable to register deployment mbean persistence.unit:unitName=#pop
javax.management.InstanceAlreadyExistsException: jboss.deployment:id="persistence.unit:unitName=#pop",type=Component already registered.
at org.jboss.mx.server.registry.BasicMBeanRegistry.add(BasicMBeanRegistry.java:756)
at org.jboss.mx.server.registry.BasicMBeanRegistry.registerMBean(BasicMBeanRegistry.java:233)在每次jboss启动成功后，马上就会出现如上错误，但是不影响项目，所以就没多处理，不知谁是否也遇见这样的问题
jboss启动时会自动加载persistence unit的
没必要在spring里再配置一遍
spring里使用直接用jndi引用jboss启动的pu就行了
网上找找 应该有很多类似的配置的
从异常来看是Persistence Unit初始化了两次
LS正解，异常看来是持久化上下文被注册了两次，看看是不是配置有点问题~~~~