Java 在JNDI中为EJB模块添加持久化单元

我正在使用示例代码开发一个简单的EJB模块。我试图通过soapweb服务实现CURD操作。我在persistence.xml中定义了一个持久性单元

下面是我的实现代码。问题是我无法创建PersistenceService实例，因为JNDI清单中不存在持久性单元名称

如果不使用代码注入，而是使用

EntityManagerFactory emf = Persistence.createEntityManagerFactory(PU_NAME);
em = emf.createEntityManager();

代码运行，但事务由容器管理。我正在阅读一些教程，他们提到，在这个场景中，如果用户想稍后回滚事务，他不能这样做

我能做些什么呢

用户类 DatabaseEntityManager类 PersistenceService类-从NetBeans生成的示例代码中借用

---

如果persistence.xml有一个条目

 <persistence-unit name="PU_NAME" transaction-type="JTA">

public class DatabaseEntityManager {
    PersistenceService ps_bck = null;
    public DatabaseEntityManager()
    {

    }

    public SiteUsers addUser(
        String Username,
        String LastName, boolean commit) throws Exception
    {
        AppUser appUser = new appUser(UserName, LastName);
        //AppUser is an entity class 

        PersistenceService ps = PersistenceService.getInstance();
        try
        {
            ps.beginTx();
            EntityManager em = ps.getEntityManager();
            em.persist(appUser);
            if (commit)
                ps.commitTx();
            else
                ps_bck  = ps;
        }
        catch (Exception E)
        {
            ps.rollbackTx();
        }
        finally
        {
            ps.close();
        }

        return appUser.getId();
    }

    void commitTx() throws Exception
    {
        try
        { 
            ps_bck.commitTx();
        }
        catch(Exception E)
        {
            throw E;
        }
        finally
        {
            ps_bck =null;
        }
    }
}

public class PersistenceService {
    private static String DEFAULT_PU = "pers-ejbPU";

    private static ThreadLocal<PersistenceService> instance = new ThreadLocal<PersistenceService>() {
        @Override
        protected PersistenceService initialValue() {
            return new PersistenceService();
        }
    };

    private EntityManager em;
    private UserTransaction utx;

    private PersistenceService() {
        try {
            //This code runs 
            // EntityManagerFactory emf = ersistence.createEntityManagerFactory(DEFAULT_PU);
            // em = emf.createEntityManager();

            //This code throws an exception
            this.em = (EntityManager) new InitialContext().lookup("java:comp/env/persistence/"+ DEFAULT_PU);
            this.utx = (UserTransaction) new InitialContext().lookup("java:comp/UserTransaction");
        } catch (NamingException ex) {
            throw new RuntimeException(ex);
        }
    }

    /**
     * Returns an instance of PersistenceService.
     *
     * @return an instance of PersistenceService
     */
    public static PersistenceService getInstance() {
        return instance.get();
    }

    private static void removeInstance() {
        instance.remove();
    }

    /**
     * Returns an instance of EntityManager.
     *
     * @return an instance of EntityManager
     */
    public EntityManager getEntityManager() {
        return em;
    }

    /**
     * Begins a resource transaction.
     */
    public void beginTx() {
        try {
            utx.begin();
            em.joinTransaction();
        } catch (Exception ex) {
            throw new RuntimeException(ex);
        }
    }

    /**
     * Commits a resource transaction.
     */
    public void commitTx() {
        try {
            utx.commit();
        } catch (Exception ex) {
            throw new RuntimeException(ex);
        }
    }

    /**
     * Rolls back a resource transaction.
     */
    public void rollbackTx() {
        try {
            utx.rollback();
        } catch (Exception ex) {
            throw new RuntimeException(ex);
        }
    }

    /**
     * Closes this instance.
     */
    public void close() {
        removeInstance();
    }
}

 <persistence-unit name="PU_NAME" transaction-type="JTA">

@PersistenceContext (name = "PU_NAME") private EntityManager em;