框架技术--hibernate jpa异常（Exception Description: Unable to acquire a connection from driver [null], use）

使用hibernate JPA在本地部署调试都没有问题，但是打成war包，放到服务后，就会抛出异常。

[#|2013-12-11T12:28:23.947+0800|SEVERE|glassfish3.1.2|javax.enterprise.system.std.com.sun.enterprise.server.logging|_ThreadID=25;_ThreadName=Thread-2;|javax.persistence.PersistenceException: Exception [EclipseLink-4021] (Eclipse Persistence Services - 2.3.2.v20111125-r10461): org.eclipse.persistence.exceptions.DatabaseException
Exception Description: Unable to acquire a connection from driver [null], user [null] and URL [null].  Verify that you have set the expected driver class and URL.  
Check your login, persistence.xml or sessions.xml resource.  
The jdbc.driver property should be set to a class that is compatible with your database platform
	at org.eclipse.persistence.internal.jpa.EntityManagerSetupImpl.deploy(EntityManagerSetupImpl.java:517)
	at org.eclipse.persistence.internal.jpa.EntityManagerFactoryDelegate.getDatabaseSession(EntityManagerFactoryDelegate.java:188)
	at org.eclipse.persistence.internal.jpa.EntityManagerFactoryDelegate.createEntityManagerImpl(EntityManagerFactoryDelegate.java:277)
	at org.eclipse.persistence.internal.jpa.EntityManagerFactoryImpl.createEntityManagerImpl(EntityManagerFactoryImpl.java:294)
	at org.eclipse.persistence.internal.jpa.EntityManagerFactoryImpl.createEntityManager(EntityManagerFactoryImpl.java:272)
	at com.haierpip.dao.impl.AdvDaoImpl.getAdvInfo(AdvDaoImpl.java:132)
	at com.haierpip.util.AdvUtil.advStrategy(AdvUtil.java:68)
	at com.haierpip.servlet.LiveEpgServlet.doPost(LiveEpgServlet.java:131)
	at com.haierpip.servlet.LiveEpgServlet.doGet(LiveEpgServlet.java:63)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:668)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:770)
	at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1550)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:343)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:217)
	at com.haierpip.util.visitRecord.AccessFilter.doFilter(AccessFilter.java:23)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:256)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:217)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:279)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)
	at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:655)
	at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:595)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:161)
	at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:331)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:231)
	at com.sun.enterprise.v3.services.impl.ContainerMapper$AdapterCallable.call(ContainerMapper.java:317)
	at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:195)
	at com.sun.grizzly.http.ProcessorTask.invokeAdapter(ProcessorTask.java:860)
	at com.sun.grizzly.http.ProcessorTask.doProcess(ProcessorTask.java:757)
	at com.sun.grizzly.http.ProcessorTask.process(ProcessorTask.java:1056)
	at com.sun.grizzly.http.DefaultProtocolFilter.execute(DefaultProtocolFilter.java:229)
	at com.sun.grizzly.DefaultProtocolChain.executeProtocolFilter(DefaultProtocolChain.java:137)
	at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:104)
	at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:90)
	at com.sun.grizzly.http.HttpProtocolChain.execute(HttpProtocolChain.java:79)
	at com.sun.grizzly.ProtocolChainContextTask.doCall(ProtocolChainContextTask.java:54)
	at com.sun.grizzly.SelectionKeyContextTask.call(SelectionKeyContextTask.java:59)
	at com.sun.grizzly.ContextTask.run(ContextTask.java:71)
	at com.sun.grizzly.util.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:532)
	at com.sun.grizzly.util.AbstractThreadPool$Worker.run(AbstractThreadPool.java:513)
	at java.lang.Thread.run(Thread.java:662)
Caused by: Exception [EclipseLink-4021] (Eclipse Persistence Services - 2.3.2.v20111125-r10461): org.eclipse.persistence.exceptions.DatabaseException
Exception Description: Unable to acquire a connection from driver [null], user [null] and URL [null].  Verify that you have set the expected driver class and URL.  Check your login, persistence.xml or sessions.xml resource.  The jdbc.driver property should be set to a class that is compatible with your database platform
	at org.eclipse.persistence.exceptions.DatabaseException.unableToAcquireConnectionFromDriverException(DatabaseException.java:376)
	at org.eclipse.persistence.sessions.DefaultConnector.connect(DefaultConnector.java:91)
	at org.eclipse.persistence.sessions.DatasourceLogin.connectToDatasource(DatasourceLogin.java:162)
	at org.eclipse.persistence.internal.sessions.DatabaseSessionImpl.loginAndDetectDatasource(DatabaseSessionImpl.java:584)
	at org.eclipse.persistence.internal.jpa.EntityManagerFactoryProvider.login(EntityManagerFactoryProvider.java:206)
	at org.eclipse.persistence.internal.jpa.EntityManagerSetupImpl.deploy(EntityManagerSetupImpl.java:488)
	... 39 more
|#]

经一番搜索，找到点有用的资料： http://www.coderanch.com/t/502791/ORM/databases/exception-JPA-application

修改persistence.xmll配置文件中连接数据库参数即可使用：

<property name="javax.persistence.jdbc.url" value="jdbc:mysql://localhost/experiments"/> 
<property name="javax.persistence.jdbc.user" value="root"/> 
<property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver"/> 
<property name="javax.persistence.jdbc.password" value=""/> 
<property name="eclipelink.ddl-generation" value="create-tables"/> 
<property name="eclipelink.jdbc.connections.min" value="1"/> 
<property name="eclipelink.jdbc.connections.max" value="2"/> 
<property name="eclipelink.logging.level" value="FINEST"/>

至于原因还需要查找。