我正在尝试创建一个简单的JPA2应用程序，它使用OpenJPA实现将某些东西保存到数据库中。我正在运行Derby并使用默认的嵌入式JDBC驱动程序。我一直在试图找出遗漏的东西。我确信这是微不足道的，但如果有人能够看到这一点并指出我正确的方向，我会非常高兴。感谢。
这是我的persistence.xml：
<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.0" xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd">
<persistence-unit name="HelloWorld">
<jta-data-source>java:comp/env/StuffDerby</jta-data-source>
<class>helloworld.entities.Employee</class>
</persistence-unit>
</persistence>
当我运行此代码时：
EntityManagerFactory emf = Persistence.createEntityManagerFactory("HelloWorld");
EntityManager em = emf.createEntityManager();
调用createEntityManager（）方法时失败。
406 HelloWorld INFO [WebContainer : 0] openjpa.Runtime - Starting OpenJPA 2.0.0
[1/11/11 12:46:21:377 PST] 0000002f servlet E com.ibm.ws.webcontainer.servlet.ServletWrapper service SRVE0068E: Uncaught exception created in one of the service methods of the servlet HelloServlet in application HelloWorld. Exception created : <openjpa-2.0.0-r422266:935683 nonfatal general error> org.apache.openjpa.persistence.PersistenceException: java.lang.String incompatible with javax.sql.DataSource
at org.apache.openjpa.kernel.AbstractBrokerFactory.newBroker(AbstractBrokerFactory.java:208)
at org.apache.openjpa.kernel.DelegatingBrokerFactory.newBroker(DelegatingBrokerFactory.java:156)
at org.apache.openjpa.persistence.EntityManagerFactoryImpl.createEntityManager(EntityManagerFactoryImpl.java:213)
at com.ibm.ws.persistence.EntityManagerFactoryImpl.createEntityManager(EntityManagerFactoryImpl.java:45)
at com.ibm.ws.persistence.EntityManagerFactoryImpl.createEntityManager(EntityManagerFactoryImpl.java:30)
at helloworld.entities.controller.EmployeeManager.getEntityManager(EmployeeManager.java:37)
at helloworld.entities.controller.EmployeeManager.getEmployee(EmployeeManager.java:188)
at helloworld.HelloServlet.doGet(HelloServlet.java:47)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:718)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:831)
at com.ibm.ws.webcontainer.servlet.ServletWrapper.service(ServletWrapper.java:1661)
at com.ibm.ws.webcontainer.servlet.ServletWrapper.service(ServletWrapper.java:1595)
at com.ibm.ws.webcontainer.filter.WebAppFilterChain.doFilter(WebAppFilterChain.java:131)
at com.ibm.ws.osgi.web.extender.OsgiDirectoryProtectionFilter.doFilter(OsgiDirectoryProtectionFilter.java:94)
at com.ibm.ws.webcontainer.filter.FilterInstanceWrapper.doFilter(FilterInstanceWrapper.java:188)
at com.ibm.ws.webcontainer.filter.WebAppFilterChain.doFilter(WebAppFilterChain.java:116)
at com.ibm.ws.webcontainer.filter.WebAppFilterChain._doFilter(WebAppFilterChain.java:77)
at com.ibm.ws.webcontainer.filter.WebAppFilterManager.doFilter(WebAppFilterManager.java:908)
at com.ibm.ws.webcontainer.servlet.ServletWrapper.handleRequest(ServletWrapper.java:932)
at com.ibm.ws.webcontainer.servlet.ServletWrapper.handleRequest(ServletWrapper.java:500)
at com.ibm.ws.webcontainer.servlet.ServletWrapperImpl.handleRequest(ServletWrapperImpl.java:178)
at com.ibm.ws.webcontainer.webapp.WebApp.handleRequest(WebApp.java:3826)
at com.ibm.ws.webcontainer.webapp.WebGroup.handleRequest(WebGroup.java:276)
at com.ibm.ws.webcontainer.WebContainer.handleRequest(WebContainer.java:931)
at com.ibm.ws.webcontainer.WSWebContainer.handleRequest(WSWebContainer.java:1583)
at com.ibm.ws.webcontainer.channel.WCChannelLink.ready(WCChannelLink.java:186)
at com.ibm.ws.http.channel.inbound.impl.HttpInboundLink.handleDiscrimination(HttpInboundLink.java:455)
at com.ibm.ws.http.channel.inbound.impl.HttpInboundLink.handleNewInformation(HttpInboundLink.java:384)
at com.ibm.ws.http.channel.inbound.impl.HttpInboundLink.ready(HttpInboundLink.java:272)
at com.ibm.ws.tcp.channel.impl.NewConnectionInitialReadCallback.sendToDiscriminators(NewConnectionInitialReadCallback.java:214)
at com.ibm.ws.tcp.channel.impl.NewConnectionInitialReadCallback.complete(NewConnectionInitialReadCallback.java:113)
at com.ibm.ws.tcp.channel.impl.AioReadCompletionListener.futureCompleted(AioReadCompletionListener.java:165)
at com.ibm.io.async.AbstractAsyncFuture.invokeCallback(AbstractAsyncFuture.java:217)
at com.ibm.io.async.AsyncChannelFuture.fireCompletionActions(AsyncChannelFuture.java:161)
at com.ibm.io.async.AsyncFuture.completed(AsyncFuture.java:138)
at com.ibm.io.async.ResultHandler.complete(ResultHandler.java:204)
at com.ibm.io.async.ResultHandler.runEventProcessingLoop(ResultHandler.java:775)
at com.ibm.io.async.ResultHandler$2.run(ResultHandler.java:905)
at com.ibm.ws.util.ThreadPool$Worker.run(ThreadPool.java:1550)
Caused by: java.lang.ClassCastException: java.lang.String incompatible with javax.sql.DataSource
at org.apache.openjpa.jdbc.conf.JDBCConfigurationImpl.createConnectionFactory(JDBCConfigurationImpl.java:834)
at org.apache.openjpa.jdbc.conf.JDBCConfigurationImpl.getDBDictionaryInstance(JDBCConfigurationImpl.java:594)
at org.apache.openjpa.jdbc.meta.MappingRepository.endConfiguration(MappingRepository.java:1489)
at org.apache.openjpa.lib.conf.Configurations.configureInstance(Configurations.java:507)
at org.apache.openjpa.lib.conf.Configurations.configureInstance(Configurations.java:432)
at org.apache.openjpa.lib.conf.PluginValue.instantiate(PluginValue.java:104)
at org.apache.openjpa.conf.MetaDataRepositoryValue.instantiate(MetaDataRepositoryValue.java:68)
at org.apache.openjpa.lib.conf.ObjectValue.instantiate(ObjectValue.java:83)
at org.apache.openjpa.conf.OpenJPAConfigurationImpl.newMetaDataRepositoryInstance(OpenJPAConfigurationImpl.java:939)
at org.apache.openjpa.conf.OpenJPAConfigurationImpl.getMetaDataRepositoryInstance(OpenJPAConfigurationImpl.java:930)
at org.apache.openjpa.kernel.AbstractBrokerFactory.makeReadOnly(AbstractBrokerFactory.java:626)
at org.apache.openjpa.kernel.AbstractBrokerFactory.newBroker(AbstractBrokerFactory.java:193)
... 38 more
答案 0 :(得分：2)
org.apache.openjpa.persistence.PersistenceException: java.lang.String incompatible with javax.sql.DataSource
换句话说，java:comp/env/StuffDerby指向java.lang.String而不是java.sql.DataSource。在服务器配置中相应地修复它。