j2ee 持久化框架——jpa实例

package cn.com.Manager; import java.util.Properties; import javax.persistence.EntityManager; import javax.persistence.EntityManagerFactory; import javax.persistence.Persistence; import cn.com.Beans.Test; public class BaseEntityManager { private static final Properties jpaProperties = new Properties(); private static final EntityManagerFactory factory = Persistence.createEntityManagerFactory("food",jpaProperties); private static final ThreadLocal<EntityManager> tl = new ThreadLocal<EntityManager>(); public static EntityManager getEntityManager(){ EntityManager em = (EntityManager)tl.get(); if(em == null||em.isOpen()){ em = factory.createEntityManager(); tl.set(em); } return em; } public static void closeEntityManager(){ EntityManager em = (EntityManager)tl.get(); if (em != null) em.close(); tl.set(null); } public static void main(String[] args){ EntityManager em = BaseEntityManager.getEntityManager(); BaseEntityManager entityManager=new BaseEntityManager(); //测试修改方法; //entityManager.testmerge(em); //测试添加方法; entityManager.testsave(em); //测试查询方法 //entityManager.testfind(em); //测试删除方法 //entityManager.testdel(em); } //测试修改方法; public void testmerge(EntityManager em) { em.getTransaction().begin(); Test tx = new Test(); tx.setId(1); tx.setName("shxt"); em.merge(tx); em.getTransaction().commit(); BaseEntityManager.closeEntityManager(); } //测试添加方法; public void testsave(EntityManager em) { em.getTransaction().begin(); Test ts=new Test(); ts.setName("shxt2"); em.persist(ts); em.getTransaction().commit(); BaseEntityManager.closeEntityManager(); } //测试查询方法 public void testfind(EntityManager em) { em.getTransaction().begin(); Test ts=new Test(); ts.setId(1); ts.setName("guolei"); System.out.println("@@@@@@@@@@@@@@@"+em.find(Test.class, ts.getId())); em.getTransaction().commit(); BaseEntityManager.closeEntityManager(); } //测试删除方法 public void testdel(EntityManager em) { em.getTransaction().begin(); Test ts=new Test(); //如果直接用删除方法删除,删除的是游离态对象,在这里删除的应该是持久态对象.所以应该先查询,然后删除查询到的对象. ts.setId(51); Test t=em.find(Test.class, ts.getId()); em.remove(t); em.getTransaction().commit(); BaseEntityManager.closeEntityManager(); } }