Java回顾之ORM框架

这篇文章里，我们主要讨论ORM框架，以及在使用上和JDBC的区别。

　　概述

　　ORM框架不是一个新话题，它已经流传了很多年。它的优点在于提供了概念性的、易于理解的数据模型，将数据库中的表和内存中的对象建立了很好的映射关系。

　　我们在这里主要关注Java中常用的两个ORM框架：Hibernate和iBatis。下面来介绍这两个框架简单的使用方法，如果将来有时间，我会深入的写一些更有意思的相关文章。

　　Hibernate

　　Hibernate是一个持久化框架和ORM框架，持久化和ORM是两个有区别的概念，持久化注重对象的存储方法是否随着程序的退出而消亡，ORM关注的是如何在数据库表和内存对象之间建立关联。

　　Hibernate使用POJO来表示Model，使用XML配置文件来配置对象和表之间的关系，它提供了一系列API来通过对对象的操作而改变数据库中的过程。

　　Hibernate更强调如何对单条记录进行操作，对于更复杂的操作，它提供了一种新的面向对象的查询语言：HQL。

　　我们先来定义一个关于Hibernate中Session管理的类，这里的Session类似于JDBC中的Connection。

 public class HibernateSessionManager {

     private static SessionFactory sessionFactory;

     static
     {
         try
         {
             sessionFactory = new Configuration().configure("sample/orm/hibernate/hibernate.cfg.xml").buildSessionFactory();
         }
         catch(Exception ex)
         {
             ex.printStackTrace();
         }
     }

     public static final ThreadLocal tl = new ThreadLocal();

     public static Session currentSession()
     {
         Session s = (Session)tl.get();
         if (s == null)
         {
             s = sessionFactory.openSession();
             tl.set(s);
         }

         return s;
     }

     public static void closeSession()
     {
         Session s = (Session)tl.get();
         tl.set(null);
         if (s != null)
         {
             s.close();
         }
     }
 }

　　基于单张表进行操作

　　下面我们来看一个简单的示例，它沿用了Java回顾之JDBC中的数据库，使用MySQL的test数据库中的user表。

　　首先，我们来定义VO对象：

 public class User implements Serializable
 {
     private static final long serialVersionUID = 1L;
     private int userID;
     private String userName;
     public void setUserID(int userID) {
         this.userID = userID;
     }
     public int getUserID() {
         return userID;
     }
     public void setUserName(String userName) {
         this.userName = userName;
     }
     public String getUserName() {
         return userName;
     }
 }

　　然后，我们定义User对象和数据库中user表之间的关联，user表中只有两列：id和name。

 <?xml version="1.0"?>
 <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
 "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

 <hibernate-mapping>
     <class name="sample.orm.hibernate.User" table="user" catalog="test">
         <id name="userID" type="java.lang.Integer">
             <column name="id" />
             <generator class="assigned" />
         </id>
         <property name="userName" type="java.lang.String">
             <column name="name" />
         </property>
     </class>
 </hibernate-mapping>

　　将上述内容存储为User.hbm.xml。

　　接下来，我们需要定义一个关于Hibernate的全局配置文件，这里文件名是hibernate.cfg.xml。

 <?xml version='1.0' encoding='UTF-8'?>
 <!DOCTYPE hibernate-configuration PUBLIC
           "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
           "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">

 <hibernate-configuration>
     <session-factory>
         <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
         <property name="connection.url">jdbc:mysql://localhost/test</property>
         <property name="connection.username">root</property>
         <property name="connection.password">123</property>
         <property name="dialect">org.hibernate.dialect.MySQLDialect</property>
         <property name="show_sql">true</property>
         <property name="jdbc.fetch_size">50</property>
         <property name="jdbc.batch_size">25</property>

         <mapping resource="sample/orm/hibernate/User.hbm.xml" /> 
     </session-factory>
 </hibernate-configuration>

　　可以看到，上述配置文件中包含了数据库连接的信息，诸如driver信息、数据库url、用户名、密码等等，还包括了我们上面定义的User.hbm.xml。

　　最后，我们编写测试代码，来对user表进行增、删、查、改的操作：

 private static void getUser(int id)
 {
     Session session = HibernateSessionManager.currentSession();
     System.out.println("=====Query test=====");
     User user = (User)session.get(User.class, new Integer(id));
     if (user != null)
     {
         System.out.println("ID:" + user.getUserID() + "; Name:" + user.getUserName());
     }
     HibernateSessionManager.closeSession();
 }

 private static void insertUser()
 {
     Session session = HibernateSessionManager.currentSession();
     System.out.println("=====Insert test=====");
     Transaction transaction = session.beginTransaction();
     User user = new User();
     user.setUserID(6);
     user.setUserName("Zhang Fei");
     session.save(user);
     session.flush();
     transaction.commit();
     HibernateSessionManager.closeSession();
     getUser(6);
 }

 private static void updateUser(int id)
 {
     Session session = HibernateSessionManager.currentSession();
     System.out.println("=====Update test=====");
     Transaction transaction = session.beginTransaction();
     User user = (User)session.get(User.class, new Integer(id));
     System.out.println("=====Before Update=====");
     if (user != null)
     {
         System.out.println("ID:" + user.getUserID() + "; Name:" + user.getUserName());
     }
     user.setUserName("Devil");
     session.save(user);
     session.flush();
     transaction.commit();
     user = (User)session.get(User.class, new Integer(id));
     System.out.println("=====After Update=====");
     if (user != null)
     {
         System.out.println("ID:" + user.getUserID() + "; Name:" + user.getUserName());
     }
     HibernateSessionManager.closeSession();
 }

 private static void deleteUser(int id)
 {
     Session session = HibernateSessionManager.currentSession();
     System.out.println("=====Delete test=====");
     Transaction transaction = session.beginTransaction();
     User user = (User)session.get(User.class, new Integer(id));
     System.out.println("=====Before Delte=====");
     if (user != null)
     {
         System.out.println("ID:" + user.getUserID() + "; Name:" + user.getUserName());
     }
     session.delete(user);
     transaction.commit();
     user = (User)session.get(User.class, new Integer(id));
     System.out.println("=====After Update=====");
     if (user != null)
     {
         System.out.println("ID:" + user.getUserID() + "; Name:" + user.getUserName());
     }
     else
     {
         System.out.println("Delete successfully.");
     }
     HibernateSessionManager.closeSession();
 }

　　我们按照如下顺序调用测试代码：

 insertUser();
 updateUser(6);
 deleteUser(6);

　　可以看到如下结果：

=====Insert test=====
Hibernate: insert into test.user (name, id) values (?, ?)
=====Query test=====
Hibernate: select user0_.id as id0_, user0_.name as name0_0_ from test.user user0_ where user0_.id=?
ID:6; Name:Zhang Fei
=====Update test=====
Hibernate: select user0_.id as id0_, user0_.name as name0_0_ from test.user user0_ where user0_.id=?
=====Before Update=====
ID:6; Name:Zhang Fei
Hibernate: update test.user set name=? where id=?
=====After Update=====
ID:6; Name:Devil
=====Delete test=====
Hibernate: select user0_.id as id0_, user0_.name as name0_0_ from test.user user0_ where user0_.id=?
=====Before Delte=====
ID:6; Name:Devil
Hibernate: delete from test.user where id=?
Hibernate: select user0_.id as id0_, user0_.name as name0_0_ from test.user user0_ where user0_.id=?
=====After Delete=====
Delete successfully.

　　请注意，上面的结果中，输出了每次数据库操作时的SQL语句，这是因为在配置文件中有如下配置：

<property name="show_sql">true</property>

　　我们可以在开发调试阶段将其打开，在部署到客户方时，将其关闭。

　　基于多表关联的操作

　　Hibernate在建立多表关联时，根据主外键的设置，表之间的关联可以分为三种：一对一、一对多和多对多。这些关联会体现在表的配置文件以及VO中。

　　下面我们来看一个经典的多表关联示例：排课表。数据库中建立如下四张表：Grade/Class/ClassRoom/Schedule。刚发现，使用MySQL自带的管理器导出表定义基本是一件不可能的任务。。。。

　　上述各表除ID以及必要外键外，只有Name一列。

　　然后看各个VO的定义：

 package sample.orm.hibernate;

 import java.io.Serializable;
 import java.util.Set;

 public class Grade implements Serializable
 {
     private static final long serialVersionUID = 1L;
     private int gradeID;
     private String gradeName;
     private Set classes;
     public void setGradeID(int gradeID) {
         this.gradeID = gradeID;
     }
     public int getGradeID() {
         return gradeID;
     }
     public void setGradeName(String gradeName) {
         this.gradeName = gradeName;
     }
     public String getGradeName() {
         return gradeName;
     }
     public void setClasses(Set classes) {
         this.classes = classes;
     }
     public Set getClasses() {
         return classes;
     }
 }

 package sample.orm.hibernate;

 import java.io.Serializable;
 import java.util.Set;

 public class Class implements Serializable
 {
     private static final long serialVersionUID = 1L;
     private int classID;
     private Grade grade;
     private Set classrooms;
     private String className;
     public void setClassID(int classID) {
         this.classID = classID;
     }
     public int getClassID() {
         return classID;
     }
     public void setClassName(String className) {
         this.className = className;
     }
     public String getClassName() {
         return className;
     }
     public void setGrade(Grade grade) {
         this.grade = grade;
     }
     public Grade getGrade() {
         return grade;
     }
     public void setClassrooms(Set classrooms) {
         this.classrooms = classrooms;
     }
     public Set getClassrooms() {
         return classrooms;
     }
 }

 package sample.orm.hibernate;

 import java.io.Serializable;
 import java.util.Set;

 public class ClassRoom implements Serializable
 {
     private static final long serialVersionUID = 1L;
     private int classRoomID;
     private String classRoomName;
     private Set classes;
     public void setClassRoomID(int classRoomID) {
         this.classRoomID = classRoomID;
     }
     public int getClassRoomID() {
         return classRoomID;
     }
     public void setClassRoomName(String classRoomName) {
         this.classRoomName = classRoomName;
     }
     public String getClassRoomName() {
         return classRoomName;
     }
     public void setClasses(Set classes) {
         this.classes = classes;
     }
     public Set getClasses() {
         return classes;
     }
 }

 package sample.orm.hibernate;

 import java.io.Serializable;
 import java.util.Set;

 public class Schedule implements Serializable
 {
     private static final long serialVersionUID = 1L;
     private int scheduleID;
     private int classRoomID;
     private int classID;
     private Set classes;
     public void setClassRoomID(int classRoomID) {
         this.classRoomID = classRoomID;
     }
     public int getClassRoomID() {
         return classRoomID;
     }
     public void setClassID(int classID) {
         this.classID = classID;
     }
     public int getClassID() {
         return classID;
     }
     public void setClasses(Set classes) {
         this.classes = classes;
     }
     public Set getClasses() {
         return classes;
     }
     public void setScheduleID(int scheduleID) {
         this.scheduleID = scheduleID;
     }
     public int getScheduleID() {
         return scheduleID;
     }
 }

　　接着是各个表的关联配置文件：

　　1）Grade.hbm.xml

 <?xml version="1.0"?>
 <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
 "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

 <hibernate-mapping>
     <class name="sample.orm.hibernate.Grade" table="grade" catalog="test">
         <id name="gradeID" type="java.lang.Integer">
             <column name="gradeid" />
             <generator class="assigned" />
         </id>
         <property name="gradeName" type="java.lang.String">
             <column name="gradename" />
         </property>

         <set name="classes" lazy="true" inverse="true" cascade="all-delete-orphan">
             <key>
                 <column name="gradeid"/>
             </key>
             <one-to-many class="sample.orm.hibernate.Class"/>
         </set>
     </class>
 </hibernate-mapping>

　　注意上面的<set>配置，里面的<one-to-many>节点说明了Grade和Class之间一对多的关系。

　　2）Class.hbm.xml

 <?xml version="1.0"?>
 <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
 "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

 <hibernate-mapping>
     <class name="sample.orm.hibernate.Class" table="class" catalog="test">
         <id name="classID" type="java.lang.Integer">
             <column name="classid" />
             <generator class="assigned" />
         </id>
         <property name="className" type="java.lang.String">
             <column name="classname" />
         </property>

         <many-to-one name="grade" class="sample.orm.hibernate.Grade" lazy="proxy" not-null="true">
             <column name="gradeid"/>
         </many-to-one>

         <set name="classrooms" lazy="true" inverse="true" cascade="all-delete-orphan" table="schedule">
             <key column ="classid"/>
             <many-to-many class="sample.orm.hibernate.ClassRoom" column="classroomid"/>
         </set>
     </class>
 </hibernate-mapping>

　　注意它定义两个关联：一个是和Grade之间多对一的关系，一个适合ClassRoom之间多对多的关系。

　　3）ClassRoom.hbm.xml

 <?xml version="1.0"?>
 <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
 "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

 <hibernate-mapping>
     <class name="sample.orm.hibernate.ClassRoom" table="classroom" catalog="test">
         <id name="classRoomID" type="java.lang.Integer">
             <column name="classroomid" />
             <generator class="assigned" />
         </id>
         <property name="classRoomName" type="java.lang.String">
             <column name="classroomname" />
         </property>

         <set name="classes" lazy="true" inverse="true" cascade="all-delete-orphan" table="schedule">
             <key column="classroomid"/>
             <many-to-many class="sample.orm.hibernate.Class" column="classid"/>
         </set>
     </class>
 </hibernate-mapping>

　　它只定义了一个关联：和Class之间的多对多关联。

　　4）Schedule.hbm.xml

 <?xml version="1.0"?>
 <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
 "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

 <hibernate-mapping>
     <class name="sample.orm.hibernate.Schedule" table="schedule" catalog="test">
         <id name="scheduleID" type="java.lang.Integer">
             <column name="scheduleid" />
             <generator class="assigned" />
         </id>
         <property name="classID" type="java.lang.Integer">
             <column name="classid" />
         </property>
         <property name="classRoomID" type="java.lang.Integer">
             <column name="classroomid" />
         </property>
     </class>
 </hibernate-mapping>

　　这里就不需要再定义关联了。

　　我们需要在Hibernate全局配置文件中添加如下内容：

 <mapping resource="sample/orm/hibernate/Grade.hbm.xml" />
 <mapping resource="sample/orm/hibernate/Class.hbm.xml" />
 <mapping resource="sample/orm/hibernate/ClassRoom.hbm.xml" />
 <mapping resource="sample/orm/hibernate/Schedule.hbm.xml" />

　　下面是各种测试方法，在有关联的情况下，Hibernate提供了下面几个特性：

• 延迟加载
• 级联添加
• 级联修改
• 级联删除

 private static void getClass(int gradeid)
 {
     Session session = HibernateSessionManager.currentSession();
     System.out.println("=====Get Class info=====");
     Transaction transaction = session.beginTransaction();
     Grade grade = (Grade)session.get(Grade.class, new Integer(gradeid));

     Hibernate.initialize(grade);
     Iterator iterator = grade.getClasses().iterator();
     System.out.println("年级：" + grade.getGradeName() + "包括以下班级：");
     while(iterator.hasNext())
     {
         System.out.println(grade.getGradeName() + ((Class)iterator.next()).getClassName());
     }
     HibernateSessionManager.closeSession();
 }

 private static void getSchedule(int gradeid)
 {
     Session session = HibernateSessionManager.currentSession();
     Transaction transaction = session.beginTransaction();
     Grade grade = (Grade)session.get(Grade.class, new Integer(gradeid));
     if (grade != null)
     {
         System.out.println("ID:" + grade.getGradeID() + "; Name:" + grade.getGradeName());
     }

     Hibernate.initialize(grade.getClasses());

     Iterator iterator = grade.getClasses().iterator();
     while(iterator.hasNext())
     {
         Class c = (Class)iterator.next();
         System.out.println(grade.getGradeName() + c.getClassName() + "使用以下教室：");
         Hibernate.initialize(c.getClassrooms());
         Iterator iterator1 = c.getClassrooms().iterator();
         while(iterator1.hasNext())
         {
             System.out.println(((ClassRoom)iterator1.next()).getClassRoomName());
         }
     }
     HibernateSessionManager.closeSession();
 }

 private static void insertGrade()
 {
     Session session = HibernateSessionManager.currentSession();
     Transaction transaction = session.beginTransaction();
     Grade grade = new Grade();
     grade.setGradeID(4);
     grade.setGradeName("四年级");

     Class c1 = new Class();
     c1.setClassID(7);
     c1.setGrade(grade);
     c1.setClassName("一班");
     Class c2 = new Class();
     c2.setClassID(8);
     c2.setGrade(grade);
     c2.setClassName("二班");

     Set set = new HashSet();
     set.add(c1);
     set.add(c2);

     grade.setClasses(set);

     session.save(grade);
     session.flush();
     transaction.commit();
     HibernateSessionManager.closeSession();
     getClass(4);
 }

 private static void deleteGrade(int gradeid)
 {
     Session session = HibernateSessionManager.currentSession();
     Transaction transaction = session.beginTransaction();
     Grade grade = (Grade)session.get(Grade.class, new Integer(gradeid));
     if (grade != null)
     {
         session.delete(grade);
         session.flush();
     }

     transaction.commit();

     grade = (Grade)session.get(Grade.class, new Integer(gradeid));
     if (grade == null)
     {
         System.out.println("删除成功");
     }
     HibernateSessionManager.closeSession();
 }

 private static void updateGrade1(int gradeid)
 {
     Session session = HibernateSessionManager.currentSession();
     Transaction transaction = session.beginTransaction();
     Grade grade = (Grade)session.get(Grade.class, new Integer(gradeid));
     if (grade != null)
     {
         System.out.println("ID:" + grade.getGradeID() + "; Name:" + grade.getGradeName());
     }
     grade.setGradeName("Grade " + gradeid);
     session.save(grade);
     session.flush();
     transaction.commit();
     HibernateSessionManager.closeSession();
     getClass(gradeid);
 }

 private static void updateGrade2(int gradeid)
 {
     Session session = HibernateSessionManager.currentSession();
     Transaction transaction = session.beginTransaction();
     Grade grade = (Grade)session.get(Grade.class, new Integer(gradeid));
     if (grade != null)
     {
         System.out.println("ID:" + grade.getGradeID() + "; Name:" + grade.getGradeName());
     }

     Grade newGrade = new Grade();
     newGrade.setGradeID(10);
     newGrade.setGradeName(grade.getGradeName());
     Set set = grade.getClasses();
     Set newSet = new HashSet();
     Iterator iterator = set.iterator();
     while(iterator.hasNext())
     {
         Class c = (Class)iterator.next();
         Class temp = new Class();
         temp.setClassID(c.getClassID());
         temp.setClassName(c.getClassName());
         temp.setGrade(newGrade);
         newSet.add(temp);
     }
     newGrade.setClasses(newSet);
     session.delete(grade);
     session.flush();
     session.save(newGrade);
     session.flush();
     transaction.commit();
     grade = (Grade)session.get(Grade.class, new Integer(gradeid));
     if (grade == null)
     {
         System.out.println("删除成功");
     }
     HibernateSessionManager.closeSession();
     getClass(10);
 }

　　按顺序调用上面的方法：

 getClass(1);
 getSchedule(1);
 insertGrade();
 updateGrade1(4);
 updateGrade2(4);
 deleteGrade(10);

　　执行结果如下：

=====Get Class info=====
Hibernate: select grade0_.gradeid as gradeid0_, grade0_.gradename as gradename1_0_ from test.grade grade0_ where grade0_.gradeid=?
Hibernate: select classes0_.gradeid as gradeid1_, classes0_.classid as classid1_, classes0_.classid as classid0_, classes0_.classname as classname2_0_, classes0_.gradeid as gradeid2_0_ from test.class classes0_ where classes0_.gradeid=?
年级：一年级包括以下班级：
一年级二班
一年级一班
Hibernate: select grade0_.gradeid as gradeid0_, grade0_.gradename as gradename1_0_ from test.grade grade0_ where grade0_.gradeid=?
ID:1; Name:一年级
Hibernate: select classes0_.gradeid as gradeid1_, classes0_.classid as classid1_, classes0_.classid as classid0_, classes0_.classname as classname2_0_, classes0_.gradeid as gradeid2_0_ from test.class classes0_ where classes0_.gradeid=?
一年级一班使用以下教室：
Hibernate: select classrooms0_.classid as classid1_, classrooms0_.classroomid as classroo2_1_, classroom1_.classroomid as classroo1_0_, classroom1_.classroomname as classroo2_4_0_ from schedule classrooms0_ inner join test.classroom classroom1_ on classrooms0_.classroomid=classroom1_.classroomid where classrooms0_.classid=?
教室二
教室五
教室一
一年级二班使用以下教室：
Hibernate: select classrooms0_.classid as classid1_, classrooms0_.classroomid as classroo2_1_, classroom1_.classroomid as classroo1_0_, classroom1_.classroomname as classroo2_4_0_ from schedule classrooms0_ inner join test.classroom classroom1_ on classrooms0_.classroomid=classroom1_.classroomid where classrooms0_.classid=?
教室四
教室二
教室六
Hibernate: select class_.classid, class_.classname as classname2_, class_.gradeid as gradeid2_ from test.class class_ where class_.classid=?
Hibernate: select class_.classid, class_.classname as classname2_, class_.gradeid as gradeid2_ from test.class class_ where class_.classid=?
Hibernate: insert into test.grade (gradename, gradeid) values (?, ?)
Hibernate: insert into test.class (classname, gradeid, classid) values (?, ?, ?)
Hibernate: insert into test.class (classname, gradeid, classid) values (?, ?, ?)
=====Get Class info=====
Hibernate: select grade0_.gradeid as gradeid0_, grade0_.gradename as gradename1_0_ from test.grade grade0_ where grade0_.gradeid=?
Hibernate: select classes0_.gradeid as gradeid1_, classes0_.classid as classid1_, classes0_.classid as classid0_, classes0_.classname as classname2_0_, classes0_.gradeid as gradeid2_0_ from test.class classes0_ where classes0_.gradeid=?
年级：四年级包括以下班级：
四年级二班
四年级一班
Hibernate: select grade0_.gradeid as gradeid0_, grade0_.gradename as gradename1_0_ from test.grade grade0_ where grade0_.gradeid=?
ID:4; Name:四年级
Hibernate: update test.grade set gradename=? where gradeid=?
=====Get Class info=====
Hibernate: select grade0_.gradeid as gradeid0_, grade0_.gradename as gradename1_0_ from test.grade grade0_ where grade0_.gradeid=?
Hibernate: select classes0_.gradeid as gradeid1_, classes0_.classid as classid1_, classes0_.classid as classid0_, classes0_.classname as classname2_0_, classes0_.gradeid as gradeid2_0_ from test.class classes0_ where classes0_.gradeid=?
年级：Grade 4包括以下班级：
Grade 4二班
Grade 4一班
Hibernate: select grade0_.gradeid as gradeid0_, grade0_.gradename as gradename1_0_ from test.grade grade0_ where grade0_.gradeid=?
ID:4; Name:Grade 4
Hibernate: select classes0_.gradeid as gradeid1_, classes0_.classid as classid1_, classes0_.classid as classid0_, classes0_.classname as classname2_0_, classes0_.gradeid as gradeid2_0_ from test.class classes0_ where classes0_.gradeid=?
Hibernate: select classrooms0_.classid as classid1_, classrooms0_.classroomid as classroo2_1_, classroom1_.classroomid as classroo1_0_, classroom1_.classroomname as classroo2_4_0_ from schedule classrooms0_ inner join test.classroom classroom1_ on classrooms0_.classroomid=classroom1_.classroomid where classrooms0_.classid=?
Hibernate: select classrooms0_.classid as classid1_, classrooms0_.classroomid as classroo2_1_, classroom1_.classroomid as classroo1_0_, classroom1_.classroomname as classroo2_4_0_ from schedule classrooms0_ inner join test.classroom classroom1_ on classrooms0_.classroomid=classroom1_.classroomid where classrooms0_.classid=?
Hibernate: delete from test.class where classid=?
Hibernate: delete from test.class where classid=?
Hibernate: delete from test.grade where gradeid=?
Hibernate: select class_.classid, class_.classname as classname2_, class_.gradeid as gradeid2_ from test.class class_ where class_.classid=?
Hibernate: select class_.classid, class_.classname as classname2_, class_.gradeid as gradeid2_ from test.class class_ where class_.classid=?
Hibernate: insert into test.grade (gradename, gradeid) values (?, ?)
Hibernate: insert into test.class (classname, gradeid, classid) values (?, ?, ?)
Hibernate: insert into test.class (classname, gradeid, classid) values (?, ?, ?)
Hibernate: select grade0_.gradeid as gradeid0_, grade0_.gradename as gradename1_0_ from test.grade grade0_ where grade0_.gradeid=?
删除成功
=====Get Class info=====
Hibernate: select grade0_.gradeid as gradeid0_, grade0_.gradename as gradename1_0_ from test.grade grade0_ where grade0_.gradeid=?
Hibernate: select classes0_.gradeid as gradeid1_, classes0_.classid as classid1_, classes0_.classid as classid0_, classes0_.classname as classname2_0_, classes0_.gradeid as gradeid2_0_ from test.class classes0_ where classes0_.gradeid=?
年级：Grade 4包括以下班级：
Grade 4一班
Grade 4二班
Hibernate: select grade0_.gradeid as gradeid0_, grade0_.gradename as gradename1_0_ from test.grade grade0_ where grade0_.gradeid=?
Hibernate: select classes0_.gradeid as gradeid1_, classes0_.classid as classid1_, classes0_.classid as classid0_, classes0_.classname as classname2_0_, classes0_.gradeid as gradeid2_0_ from test.class classes0_ where classes0_.gradeid=?
Hibernate: select classrooms0_.classid as classid1_, classrooms0_.classroomid as classroo2_1_, classroom1_.classroomid as classroo1_0_, classroom1_.classroomname as classroo2_4_0_ from schedule classrooms0_ inner join test.classroom classroom1_ on classrooms0_.classroomid=classroom1_.classroomid where classrooms0_.classid=?
Hibernate: select classrooms0_.classid as classid1_, classrooms0_.classroomid as classroo2_1_, classroom1_.classroomid as classroo1_0_, classroom1_.classroomname as classroo2_4_0_ from schedule classrooms0_ inner join test.classroom classroom1_ on classrooms0_.classroomid=classroom1_.classroomid where classrooms0_.classid=?
Hibernate: delete from test.class where classid=?
Hibernate: delete from test.class where classid=?
Hibernate: delete from test.grade where gradeid=?
Hibernate: select grade0_.gradeid as gradeid0_, grade0_.gradename as gradename1_0_ from test.grade grade0_ where grade0_.gradeid=?
删除成功

　　同样，执行结果中包含了各个SQL语句。

　　iBatis

　　iBatis是另外一种ORM框架，和Hibernate擅长操作单条记录不同，iBatis是基于SQL模板的，可以说，iBatis每次和数据库进行操作时，都有明确的SQL语句，而这些SQL语句，就是我们定义在配置文件中的。

　　我们还是以test数据库中的user表为例，简单说明iBatis的操作流程：

　　首先，我们还是需要定义VO对象，这里还是使用和Hibernate讲解时相同的User：

 package sample.orm.ibatis;

 import java.io.Serializable;

 public class User implements Serializable
 {
     private static final long serialVersionUID = 1L;
     private int userID;
     private String userName;
     public void setUserID(int userID) {
         this.userID = userID;
     }
     public int getUserID() {
         return userID;
     }
     public void setUserName(String userName) {
         this.userName = userName;
     }
     public String getUserName() {
         return userName;
     }

 }

　　然后需要针对这个VO，定义一个独立的配置文件：User.xml

 <?xml version="1.0" encoding="UTF-8"?>
 <!DOCTYPE sqlMap
     PUBLIC "-//iBATIS.com//DTD SQL Map 2.0//EN"
     "http://www.ibatis.com/dtd/sql-map-2.dtd">

 <sqlMap namespace="User">

     <typeAlias alias="user" type="sample.orm.ibatis.User" />

     <cacheModel id="user-cache" type="OSCache" readOnly="true" serialize="true">
         <flushInterval milliseconds="1" />
         <flushOnExecute statement="insertUser" />
         <flushOnExecute statement="updateUser" />
         <flushOnExecute statement="getUser" />
         <flushOnExecute statement="getAllUser" />
         <property value="1" name="size" />
      </cacheModel>

     <!--
     <resultMap >
         <result property="userID" column="id" />
         <result property="userName" column="name" />
     </resultMap>
     -->

     <select id="getUser" parameterClass="java.lang.Integer" resultClass="user" cacheModel="user-cache" >
         select id as userID,name as userName from user where id = #userID#
     </select>
     <select id="getAllUser" resultClass="user" cacheModel="user-cache">
         select id as userID,name as userName from user
     </select>
     <update id="updateUser" parameterClass="user">
         update user SET name=#userName# WHERE id = #userID#
     </update>
     <insert id="insertUser" parameterClass="user">
         insert into user ( id, name ) VALUES ( #userID#,#userName#)
     </insert>
     <delete id="deleteUser" parameterClass="java.lang.Integer">
         delete from user where id=#userID#
     </delete>

 </sqlMap>

　　这个配置文件主要包括三部分：

　　1）缓存的配置

　　2）对象属性和表字段之间的关联

　　3）针对表的各种CRUD操作

　　然后是关于iBatis的全局配置文件SqlMapConfig.xml：

 <?xml version="1.0" encoding="UTF-8"?>
 <!DOCTYPE sqlMapConfig
     PUBLIC "-//iBATIS.com//DTD SQL Map Config 2.0//EN"
     "http://www.ibatis.com/dtd/sql-map-config-2.dtd">

 <sqlMapConfig>

     <settings cacheModelsEnabled="true" enhancementEnabled="true"
         lazyLoadingEnabled="true" errorTracingEnabled="true" maxRequests="32"
         maxSessions="10" maxTransactions="5" useStatementNamespaces="false" />

     <transactionManager type="JDBC">
         <dataSource type="SIMPLE">
            <property name="JDBC.Driver" value="com.mysql.jdbc.Driver" />
            <property name="JDBC.ConnectionURL" value="jdbc:mysql://localhost/test" />
            <property name="JDBC.Username" value="root" />
            <property name="JDBC.Password" value="123" />
            <property name="Pool.MaximumActiveConnections" value="10" />
            <property name="Pool.MaximumIdleConnections" value="5" />
            <property name="Pool.MaximumCheckoutTime" value="120000" />
            <property name="Pool.TimeToWait" value="500" />
            <property name="Pool.PingQuery" value="select 1 from user" />
            <property name="Pool.PingEnabled" value="false" />
         </dataSource>
     </transactionManager>

     <sqlMap resource="sample/orm/ibatis/User.xml" />

 </sqlMapConfig>

　　和Hibernate全局配置文件类似，它也包含了数据库连接的信息、数据库连接池的信息以及我们定义的User.xml。

　　下面是测试方法：

 public class Sample {

     private SqlMapClient sqlMap = null;

     private void buildMap() throws IOException
     {
         String resource = "sample/orm/ibatis/SqlMapConfig.xml";
         Reader reader = Resources.getResourceAsReader(resource);
         this.sqlMap = SqlMapClientBuilder.buildSqlMapClient(reader);
     }

     private void insertUser() throws IOException, SQLException
     {
         System.out.println("=====Insert test=====");
         if (this.sqlMap == null)
         {
             this.buildMap();
         }
         this.sqlMap.startTransaction();
         User user = new User();
         user.setUserID(10);
         user.setUserName("Angel");

         this.sqlMap.insert("insertUser", user);
         this.sqlMap.commitTransaction();

         user = getUser(10);
         printUserInfo(user);
     }

     private void updateUser() throws IOException, SQLException, InterruptedException
     {
         System.out.println("=====Update test=====");
         if (this.sqlMap == null)
         {
             this.buildMap();
         }
         this.sqlMap.startTransaction();
         User user = new User();
         user.setUserID(10);
         user.setUserName("Devil");
         this.sqlMap.update("updateUser", user);
         this.sqlMap.commitTransaction();
         this.sqlMap.flushDataCache();
 //        Thread.sleep(3000);
         user = getUser(10);
         printUserInfo(user);
     }

     private void deleteUser() throws IOException, SQLException
     {
         System.out.println("=====Delete test=====");
         if (this.sqlMap == null)
         {
             this.buildMap();
         }
         sqlMap.flushDataCache();
         this.sqlMap.startTransaction();
         this.sqlMap.delete("deleteUser", 10);
         this.sqlMap.commitTransaction();
         getAllUser();
     }

     private User getUser(int id) throws IOException, SQLException
     {
         if (this.sqlMap == null)
         {
             this.buildMap();
         }
         User user = (User)this.sqlMap.openSession().queryForObject("getUser", id);

         return user;
     }

      private List<User> getAllUser() throws IOException, SQLException
      {
             if(this.sqlMap==null)
                this.buildMap();

          List userList=null;
          userList=this.sqlMap.openSession().queryForList("getAllUser");
          printUserInfo(userList);
          return userList;
      }

      private void printUserInfo(User user)
      {
          System.out.println("=====user info=====");
          System.out.println("ID:" + user.getUserID() + ";Name:" + user.getUserName());
      }

      private void printUserInfo(List<User> users)
      {
          System.out.println("=====user info=====");
          for(User user:users)
          {
              System.out.println("ID:" + user.getUserID() + ";Name:" + user.getUserName());
          }
      }

      public static void main(String[] args) throws IOException, SQLException, InterruptedException
      {
          Sample sample = new Sample();
          sample.getAllUser();
          sample.insertUser();
          sample.updateUser();
          sample.deleteUser();
      }
 }

　　它的执行结果如下：

=====user info=====
ID:1;Name:Zhang San
ID:2;Name:TEST
=====Insert test=====
=====user info=====
ID:10;Name:Angel
=====Update test=====
=====user info=====
ID:10;Name:Devil
=====Delete test=====
=====user info=====
ID:1;Name:Zhang San
ID:2;Name:TEST

　　这篇文章只是简单介绍了Hibernate和iBatis的用法，并没有涉及全部，例如Hibernate的事务、拦截、HQL、iBatis的缓存等等。这里主要是为了描述ORM框架的基本轮廓，以及在使用方式上它和JDBC的区别。