我将Servlet，PostgreSQL和Hibernate与EntityManager一起使用来构建Web应用程序，然后一切正常，直到将项目移至基于Maven的项目。现在，每次尝试从EntityManagerFactory创建EntityManager时，我都会得到这个奇怪的异常：

org.hibernate.resource.transaction.backend.jta.internal.JtaPlatformInaccessibleException: Unable to access TransactionManager or UserTransaction to make physical transaction delegate
at org.hibernate.resource.transaction.backend.jta.internal.JtaTransactionCoordinatorImpl.makePhysicalTransactionDelegate(JtaTransactionCoordinatorImpl.java:229)
at org.hibernate.resource.transaction.backend.jta.internal.JtaTransactionCoordinatorImpl.getTransactionDriverControl(JtaTransactionCoordinatorImpl.java:203)
at org.hibernate.engine.transaction.internal.TransactionImpl.<init>(TransactionImpl.java:36)
at org.hibernate.internal.AbstractSessionImpl.getTransaction(AbstractSessionImpl.java:309)
at org.hibernate.internal.SessionImpl.<init>(SessionImpl.java:277)
at org.hibernate.internal.SessionFactoryImpl$SessionBuilderImpl.openSession(SessionFactoryImpl.java:1322)
at org.hibernate.jpa.internal.EntityManagerImpl.internalGetSession(EntityManagerImpl.java:133)
at org.hibernate.jpa.spi.AbstractEntityManagerImpl.postInit(AbstractEntityManagerImpl.java:174)
at org.hibernate.jpa.internal.EntityManagerImpl.<init>(EntityManagerImpl.java:83)
at org.hibernate.jpa.internal.EntityManagerFactoryImpl.internalCreateEntityManager(EntityManagerFactoryImpl.java:311)
at org.hibernate.jpa.internal.EntityManagerFactoryImpl.createEntityManager(EntityManagerFactoryImpl.java:278)
at cl.bicubic.App.getEntityManager(App.java:100)
at cl.bicubic.dao.DAO.<init>(DAO.java:24)
at cl.bicubic.dao.UserAtomicDAO.<init>(UserAtomicDAO.java:15)
at cl.bicubic.Application.init(Application.java:70)
at javax.servlet.GenericServlet.init(GenericServlet.java:158)
at org.apache.catalina.core.StandardWrapper.initServlet(StandardWrapper.java:1241)
at org.apache.catalina.core.StandardWrapper.loadServlet(StandardWrapper.java:1154)
at org.apache.catalina.core.StandardWrapper.allocate(StandardWrapper.java:827)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:135)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:503)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:136)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:610)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:526)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1078)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:655)
at org.apache.coyote.http11.Http11NioProtocol$Http11ConnectionHandler.process(Http11NioProtocol.java:222)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1566)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1523)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:745)

这是持久性单元中Hibernate的配置：

<properties>
    <property name="hibernate.connection.url" value="jdbc:postgresql://localhost/mydb?charSet=UTF-8"/>
    <property name="hibernate.connection.user" value="dbuser"/>
    <property name="hibernate.connection.password" value="dbpass"/>
    <property name="hibernate.connection.driver_class" value="org.postgresql.Driver"/>
    <property name="hibernate.connection.provider_class" value="org.hibernate.connection.C3P0ConnectionProvider"/>
    <property name="hibernate.dialect" value="org.hibernate.dialect.PostgreSQL9Dialect"/>
    <property name="hibernate.c3p0.min_size" value="5"/>
    <property name="hibernate.c3p0.max_size" value="20"/>
    <property name="hibernate.c3p0.timeout" value="1800"/>
    <property name="hibernate.c3p0.max_statements" value="50"/>
    <property name="hibernate.connection.charSet" value="UTF-8"/>
    <property name="hibernate.hbm2ddl.auto" value="update"/>
    <property name="hibernate.id.new_generator_mappings" value="true"/>
    <property name="hibernate.show_sql" value="true"/>
    <property name="hibernate.format_sql" value="true"/>
</properties>

这是我创建EntityManagerFactory的方法：

public class App {
    ...
    private static EntityManagerFactory entityManagerFactory;
    ...
    public static void setServletContext(ServletContext context) throws IOException {
         ...
         entityManagerFactory = Persistence.createEntityManagerFactory("persistence-unit-name");
         ...
    }
    ...
    public static EntityManager getEntityManager() {
        return entityManagerFactory.createEntityManager(); //Here Throws the Exception
    }
    ...
}

我使用ServletContextListener调用此方法

@WebListener
public class ApplicationServletContextListener implements ServletContextListener {

    @Override
    public void contextInitialized(ServletContextEvent sce) {
        try {
            App.setServletContext(sce.getServletContext());
        } catch (Exception ex) {
           Logger.getLogger(ApplicationServletContextListener.class.getName()).log(Level.SEVERE, null, ex);
        }
    }

    ...

}

这就是我尝试创建EntityManager的方式

public class DAO {
    ...
    protected EntityManager entityManager;
    ...
    public DAO() {
        entityManager = App.getEntityManager();
        ...
    }

    ...
}

我试图寻找有关此JtaPlatformInaccessibleException起源的更多信息，但我什么都没找到。我不确定丢失了什么。