JPA 操作：PersistenceService.java

package com.emprogria.rs.service; import javax.naming.InitialContext; import javax.naming.NamingException; import javax.persistence.EntityManager; import javax.transaction.UserTransaction; public class PersistenceService { private static String DEFAULT_PU = "rsContactPU"; 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.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(); } }