在过去的几天中，我设计了一个可能的解决方案。我试图用
BookUnitSession该类构造的实际上是
EntityManagerHelper该类：
public class EntityManagerHelper { private static final EntityManagerFactory emf; private static final ThreadLocal<EntityManager> threadLocal; static { emf = Persistence.createEntityManagerFactory("BookStoreUnit"); threadLocal = new ThreadLocal<EntityManager>(); } public static EntityManager getEntityManager() { EntityManager em = threadLocal.get(); if (em == null) { em = emf.createEntityManager(); threadLocal.set(em); } return em; } public static void closeEntityManager() { EntityManager em = threadLocal.get(); if (em != null) { em.close(); threadLocal.set(null); } } public static void closeEntityManagerFactory() { emf.close(); } public static void beginTransaction() { getEntityManager().getTransaction().begin(); } public static void rollback() { getEntityManager().getTransaction().rollback(); } public static void commit() { getEntityManager().getTransaction().commit(); } }这样的类确保每个线程（即每个请求）将获得其自己的
EntityManager实例。因此，每个DAO对象可以
EntityManager通过调用获得正确的实例
EntityManagerHelper.getEntityManager()
根据每次请求会话模式，每个请求必须打开和关闭其自己的
EntityManager实例，该实例负责将事务中所需的工作单元封装起来。这可以通过实现为的拦截过滤器来完成
ServletFilter：
public class EntityManagerInterceptor implements Filter { @Override public void destroy() {} @Override public void init(FilterConfig fc) throws ServletException {} @Override public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException { try { EntityManagerHelper.beginTransaction(); chain.doFilter(req, res); EntityManagerHelper.commit(); } catch (RuntimeException e) { if ( EntityManagerHelper.getEntityManager() != null && EntityManagerHelper.getEntityManager().isOpen()) EntityManagerHelper.rollback(); throw e; } finally { EntityManagerHelper.closeEntityManager(); } }}这种方法还允许View（例如，JSP页面）获取实体的字段，即使它们已经被延迟初始化（View模式中的Open
Session）。在JSE环境中，
EntityManagerFactory当servlet容器关闭时，需要显式关闭。这可以通过使用一个
ServletContextListener对象来完成：
public class EntityManagerFactoryListener implements ServletContextListener { @Override public void contextDestroyed(ServletContextEvent e) { EntityManagerHelper.closeEntityManagerFactory(); } @Override public void contextInitialized(ServletContextEvent e) {}}在
web.xml部署描述符：
<listener> <description>EntityManagerFactory Listener</description> <listener-class>package.EntityManagerFactoryListener</listener-class></listener><filter> <filter-name>interceptor</filter-name> <filter-class>package.EntityManagerInterceptor</filter-class></filter><filter-mapping> <filter-name>interceptor</filter-name> <url-pattern>*.do</url-pattern></filter-mapping>
