Hibernate，JPA注解@Entity

通过@Entity注解将一个类声明为一个实体bean(即一个持久化POJO类), @Id注解则声明了该实体bean的标识属性. 其他的映射定义是隐式的.

就是说一个持久化POJO类，除了主键ID需要@Id显示注解，其他列都可以不做任何注解。

用例代码如下：

• 数据库DDL语句：

 create table CAT
 (
   id          VARCHAR2(32 CHAR) not null,
   create_time TIMESTAMP(6),
   update_time TIMESTAMP(6),
   cat_name    VARCHAR2(255 CHAR)
 )

• hibernate.cfg.xml

 <?xml version="1.0" encoding="utf-8" ?>
 <!DOCTYPE hibernate-configuration
  PUBLIC "-//Hibernate/Hibernate Configuration DTD//EN"
  "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
 <hibernate-configuration>
     <session-factory>
         <!-- 数据库驱动配置 -->
         <property name="dialect">org.hibernate.dialect.Oracle10gDialect</property>
         <property name="connection.driver_class">oracle.jdbc.OracleDriver</property>
         <property name="connection.url">jdbc:oracle:thin:@127.0.0.1:1521:orcl</property>
         <property name="connection.username">wxuatuser</property>
         <property name="connection.password">xlh</property>
         <property name="show_sql">true</property>
         <!-- 自动执行DDL属性是update，不是true -->
         <property name="hbm2ddl.auto">update</property>
         <!-- hibernate实体类 -->

         <mapping class="a1_Entity.Cat"/>

     </session-factory>
 </hibernate-configuration>

• java类

实体类 - 基类

 package model;
 import java.io.Serializable;
 import java.util.Date;
 import javax.persistence.Column;
 import javax.persistence.GeneratedValue;
 import javax.persistence.Id;
 import javax.persistence.MappedSuperclass;
 import org.hibernate.annotations.GenericGenerator;

 /**
  * 实体类 - 基类
  */
 @MappedSuperclass
 public class BaseEntity implements Serializable {

     private static final long serialVersionUID = -6718838800112233445L;

     private String id;// ID
     private Date create_time;// 创建日期
     private Date update_time;// 修改日期
     @Id
     @Column(length = 32, nullable = true)
     @GeneratedValue(generator = "uuid")
     @GenericGenerator(name = "uuid", strategy = "uuid")
     public String getId() {
         return id;
     }
     public void setId(String id) {
         this.id = id;
     }
     @Column(updatable = false)
     public Date getCreate_time() {
         return create_time;
     }
     public void setCreate_time(Date create_time) {
         this.create_time = create_time;
     }
     public Date getUpdate_time() {
         return update_time;
     }
     public void setUpdate_time(Date update_time) {
         this.update_time = update_time;
     }
     @Override
     public int hashCode() {
         return id == null ? System.identityHashCode(this) : id.hashCode();
     }
     @Override
     public boolean equals(Object obj) {
         if (this == obj) {
             return true;
         }
         if (obj == null) {
             return false;
         }
         if (getClass().getPackage() != obj.getClass().getPackage()) {
             return false;
         }
         final BaseEntity other = (BaseEntity) obj;
         if (id == null) {
             if (other.getId() != null) {
                 return false;
             }
         } else if (!id.equals(other.getId())) {
             return false;
         }
         return true;
     }
 }

实体类

 package a1_Entity;
 import javax.persistence.Entity;

 import model.BaseEntity;

 @Entity
 public class Cat extends BaseEntity{
     /**
      * 实体类
      */
     private static final long serialVersionUID = -2776330321385582872L;

     private String cat_name;

     public String getCat_name() {
         return cat_name;
     }

     public void setCat_name(String cat_name) {
         this.cat_name = cat_name;
     }
 }

Dao

 package daoUtil;

 import org.hibernate.HibernateException;
 import org.hibernate.Session;
 import org.hibernate.SessionFactory;
 import org.hibernate.Transaction;
 import org.hibernate.cfg.Configuration;
 import org.hibernate.service.ServiceRegistry;
 import org.hibernate.service.ServiceRegistryBuilder;

 public class HibernateUtil {

     private static final SessionFactory sessionFactory;

     static {
         try {
             Configuration cfg = new Configuration().configure();
             ServiceRegistry serviceRegistry = new ServiceRegistryBuilder()
                     .applySettings(cfg.getProperties()).buildServiceRegistry();
             sessionFactory = cfg.buildSessionFactory(serviceRegistry);
         } catch (Throwable ex) {
             // Log exception!
             throw new ExceptionInInitializerError(ex);
         }
     }

     public static Session getSession() throws HibernateException {
         return sessionFactory.openSession();
     }

     public static Object save(Object obj){
         Session session = HibernateUtil.getSession();
         Transaction tx = null;
         try {
             tx = session.beginTransaction();
             session.save(obj);
             tx.commit();
         } catch (RuntimeException e) {
             if (tx != null) {
                 tx.rollback();
             }
             throw e;
         } finally {
             session.close();
         }
         return obj;
     }

     public static void delete(Class<?> clazz,String id){
         Session session = HibernateUtil.getSession();
         Transaction tx = null;
         try {
             tx = session.beginTransaction();
             Object obj = session.get(clazz,id);
             session.delete(obj);
             tx.commit();
         } catch (RuntimeException e) {
             if (tx != null) {
                 tx.rollback();
             }
             throw e;
         } finally {
             session.close();
         }
     }
 }

main

 package a1_Entity;

 import daoUtil.HibernateUtil;

 public class Test_Entity {

     public static void main(String[] args) {
         Cat cat = new Cat();
         cat.setId("1");
         cat.setCat_name("test1@Entity");
         HibernateUtil.save(cat);
     }
 }

环境：JDK1.6，MAVEN

源码地址：http://files.cnblogs.com/files/xiluhua/hibernate%40Entity.rar