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。
1 public class HibernateSessionManager { 2
3 private static SessionFactory sessionFactory; 4
5 static
6 { 7 try
8 { 9 sessionFactory = new Configuration().configure("sample/orm/hibernate/hibernate.cfg.xml").buildSessionFactory(); 10 } 11 catch(Exception ex) 12 { 13 ex.printStackTrace(); 14 } 15 } 16
17 public static final ThreadLocal tl = new ThreadLocal(); 18
19 public static Session currentSession() 20 { 21 Session s = (Session)tl.get(); 22 if (s == null) 23 { 24 s = sessionFactory.openSession(); 25 tl.set(s); 26 } 27
28 return s; 29 } 30
31 public static void closeSession() 32 { 33 Session s = (Session)tl.get(); 34 tl.set(null); 35 if (s != null) 36 { 37 s.close(); 38 } 39 } 40 }
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：
1 public class User implements Serializable 2 { 3 private static final long serialVersionUID = 1L; 4 private int userID; 5 private String userName; 6 public void setUserID(int userID) { 7 this.userID = userID; 8 } 9 public int getUserID() { 10 return userID; 11 } 12 public void setUserName(String userName) { 13 this.userName = userName; 14 } 15 public String getUserName() { 16 return userName; 17 } 18 }
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。
1 <?xml version="1.0"?>
2 <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" 3 "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
4
5 <hibernate-mapping>
6 <class name="sample.orm.hibernate.User" table="user" catalog="test">
7 <id name="userID" type="java.lang.Integer">
8 <column name="id" />
9 <generator class="assigned" />
10 </id>
11 <property name="userName" type="java.lang.String">
12 <column name="name" />
13 </property>
14 </class>
15 </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。
1 <?xml version='1.0' encoding='UTF-8'?>
2 <!DOCTYPE hibernate-configuration PUBLIC 3 "-//Hibernate/Hibernate Configuration DTD 3.0//EN" 4 "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
5
6 <hibernate-configuration>
7 <session-factory>
8 <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
9 <property name="connection.url">jdbc:mysql://localhost/test</property>
10 <property name="connection.username">root</property>
11 <property name="connection.password">123</property>
12 <property name="dialect">org.hibernate.dialect.MySQLDialect</property>
13 <property name="show_sql">true</property>
14 <property name="jdbc.fetch_size">50</property>
15 <property name="jdbc.batch_size">25</property>
16
17 <mapping resource="sample/orm/hibernate/User.hbm.xml" />
18 </session-factory>
19 </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：
1 private static void getUser(int id) 2 { 3 Session session = HibernateSessionManager.currentSession(); 4 System.out.println("=====Query test====="); 5 User user = (User)session.get(User.class, new Integer(id)); 6 if (user != null) 7 { 8 System.out.println("ID:" + user.getUserID() + "; Name:" + user.getUserName()); 9 } 10 HibernateSessionManager.closeSession(); 11 } 12
13 private static void insertUser() 14 { 15 Session session = HibernateSessionManager.currentSession(); 16 System.out.println("=====Insert test====="); 17 Transaction transaction = session.beginTransaction(); 18 User user = new User(); 19 user.setUserID(6); 20 user.setUserName("Zhang Fei"); 21 session.save(user); 22 session.flush(); 23 transaction.commit(); 24 HibernateSessionManager.closeSession(); 25 getUser(6); 26 } 27
28 private static void updateUser(int id) 29 { 30 Session session = HibernateSessionManager.currentSession(); 31 System.out.println("=====Update test====="); 32 Transaction transaction = session.beginTransaction(); 33 User user = (User)session.get(User.class, new Integer(id)); 34 System.out.println("=====Before Update====="); 35 if (user != null) 36 { 37 System.out.println("ID:" + user.getUserID() + "; Name:" + user.getUserName()); 38 } 39 user.setUserName("Devil"); 40 session.save(user); 41 session.flush(); 42 transaction.commit(); 43 user = (User)session.get(User.class, new Integer(id)); 44 System.out.println("=====After Update====="); 45 if (user != null) 46 { 47 System.out.println("ID:" + user.getUserID() + "; Name:" + user.getUserName()); 48 } 49 HibernateSessionManager.closeSession(); 50 } 51
52 private static void deleteUser(int id) 53 { 54 Session session = HibernateSessionManager.currentSession(); 55 System.out.println("=====Delete test====="); 56 Transaction transaction = session.beginTransaction(); 57 User user = (User)session.get(User.class, new Integer(id)); 58 System.out.println("=====Before Delte====="); 59 if (user != null) 60 { 61 System.out.println("ID:" + user.getUserID() + "; Name:" + user.getUserName()); 62 } 63 session.delete(user); 64 transaction.commit(); 65 user = (User)session.get(User.class, new Integer(id)); 66 System.out.println("=====After Update====="); 67 if (user != null) 68 { 69 System.out.println("ID:" + user.getUserID() + "; Name:" + user.getUserName()); 70 } 71 else
72 { 73 System.out.println("Delete successfully."); 74 } 75 HibernateSessionManager.closeSession(); 76 }
我们按照如下顺序调用测试代码：
1 insertUser(); 2 updateUser(6); 3 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：
1 package sample.orm.hibernate; 2
3 import java.io.Serializable; 4 import java.util.Set; 5
6 public class Grade implements Serializable 7 { 8 private static final long serialVersionUID = 1L; 9 private int gradeID; 10 private String gradeName; 11 private Set classes; 12 public void setGradeID(int gradeID) { 13 this.gradeID = gradeID; 14 } 15 public int getGradeID() { 16 return gradeID; 17 } 18 public void setGradeName(String gradeName) { 19 this.gradeName = gradeName; 20 } 21 public String getGradeName() { 22 return gradeName; 23 } 24 public void setClasses(Set classes) { 25 this.classes = classes; 26 } 27 public Set getClasses() { 28 return classes; 29 } 30 }
1 package sample.orm.hibernate; 2
3 import java.io.Serializable; 4 import java.util.Set; 5
6 public class Class implements Serializable 7 { 8 private static final long serialVersionUID = 1L; 9 private int classID; 10 private Grade grade; 11 private Set classrooms; 12 private String className; 13 public void setClassID(int classID) { 14 this.classID = classID; 15 } 16 public int getClassID() { 17 return classID; 18 } 19 public void setClassName(String className) { 20 this.className = className; 21 } 22 public String getClassName() { 23 return className; 24 } 25 public void setGrade(Grade grade) { 26 this.grade = grade; 27 } 28 public Grade getGrade() { 29 return grade; 30 } 31 public void setClassrooms(Set classrooms) { 32 this.classrooms = classrooms; 33 } 34 public Set getClassrooms() { 35 return classrooms; 36 } 37 }
1 package sample.orm.hibernate; 2
3 import java.io.Serializable; 4 import java.util.Set; 5
6 public class ClassRoom implements Serializable 7 { 8 private static final long serialVersionUID = 1L; 9 private int classRoomID; 10 private String classRoomName; 11 private Set classes; 12 public void setClassRoomID(int classRoomID) { 13 this.classRoomID = classRoomID; 14 } 15 public int getClassRoomID() { 16 return classRoomID; 17 } 18 public void setClassRoomName(String classRoomName) { 19 this.classRoomName = classRoomName; 20 } 21 public String getClassRoomName() { 22 return classRoomName; 23 } 24 public void setClasses(Set classes) { 25 this.classes = classes; 26 } 27 public Set getClasses() { 28 return classes; 29 } 30 }
1 package sample.orm.hibernate; 2
3 import java.io.Serializable; 4 import java.util.Set; 5
6 public class Schedule implements Serializable 7 { 8 private static final long serialVersionUID = 1L; 9 private int scheduleID; 10 private int classRoomID; 11 private int classID; 12 private Set classes; 13 public void setClassRoomID(int classRoomID) { 14 this.classRoomID = classRoomID; 15 } 16 public int getClassRoomID() { 17 return classRoomID; 18 } 19 public void setClassID(int classID) { 20 this.classID = classID; 21 } 22 public int getClassID() { 23 return classID; 24 } 25 public void setClasses(Set classes) { 26 this.classes = classes; 27 } 28 public Set getClasses() { 29 return classes; 30 } 31 public void setScheduleID(int scheduleID) { 32 this.scheduleID = scheduleID; 33 } 34 public int getScheduleID() { 35 return scheduleID; 36 } 37 }
接着是各个表的关联配置文件：
1）Grade.hbm.xml
1 <?xml version="1.0"?>
2 <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" 3 "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
4
5 <hibernate-mapping>
6 <class name="sample.orm.hibernate.Grade" table="grade" catalog="test">
7 <id name="gradeID" type="java.lang.Integer">
8 <column name="gradeid" />
9 <generator class="assigned" />
10 </id>
11 <property name="gradeName" type="java.lang.String">
12 <column name="gradename" />
13 </property>
14
15 <set name="classes" lazy="true" inverse="true" cascade="all-delete-orphan">
16 <key>
17 <column name="gradeid"/>
18 </key>
19 <one-to-many class="sample.orm.hibernate.Class"/>
20 </set>
21 </class>
22 </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
1 <?xml version="1.0"?>
2 <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" 3 "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
4
5 <hibernate-mapping>
6 <class name="sample.orm.hibernate.Class" table="class" catalog="test">
7 <id name="classID" type="java.lang.Integer">
8 <column name="classid" />
9 <generator class="assigned" />
10 </id>
11 <property name="className" type="java.lang.String">
12 <column name="classname" />
13 </property>
14
15 <many-to-one name="grade" class="sample.orm.hibernate.Grade" lazy="proxy" not-null="true">
16 <column name="gradeid"/>
17 </many-to-one>
18
19 <set name="classrooms" lazy="true" inverse="true" cascade="all-delete-orphan" table="schedule">
20 <key column ="classid"/>
21 <many-to-many class="sample.orm.hibernate.ClassRoom" column="classroomid"/>
22 </set>
23 </class>
24 </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
1 <?xml version="1.0"?>
2 <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" 3 "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
4
5 <hibernate-mapping>
6 <class name="sample.orm.hibernate.ClassRoom" table="classroom" catalog="test">
7 <id name="classRoomID" type="java.lang.Integer">
8 <column name="classroomid" />
9 <generator class="assigned" />
10 </id>
11 <property name="classRoomName" type="java.lang.String">
12 <column name="classroomname" />
13 </property>
14
15 <set name="classes" lazy="true" inverse="true" cascade="all-delete-orphan" table="schedule">
16 <key column="classroomid"/>
17 <many-to-many class="sample.orm.hibernate.Class" column="classid"/>
18 </set>
19 </class>
20 </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
1 <?xml version="1.0"?>
2 <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" 3 "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
4
5 <hibernate-mapping>
6 <class name="sample.orm.hibernate.Schedule" table="schedule" catalog="test">
7 <id name="scheduleID" type="java.lang.Integer">
8 <column name="scheduleid" />
9 <generator class="assigned" />
10 </id>
11 <property name="classID" type="java.lang.Integer">
12 <column name="classid" />
13 </property>
14 <property name="classRoomID" type="java.lang.Integer">
15 <column name="classroomid" />
16 </property>
17 </class>
18 </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：
1 <mapping resource="sample/orm/hibernate/Grade.hbm.xml" />
2 <mapping resource="sample/orm/hibernate/Class.hbm.xml" />
3 <mapping resource="sample/orm/hibernate/ClassRoom.hbm.xml" />
4 <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
1 private static void getClass(int gradeid) 2 { 3 Session session = HibernateSessionManager.currentSession(); 4 System.out.println("=====Get Class info====="); 5 Transaction transaction = session.beginTransaction(); 6 Grade grade = (Grade)session.get(Grade.class, new Integer(gradeid)); 7
8 Hibernate.initialize(grade); 9 Iterator iterator = grade.getClasses().iterator(); 10 System.out.println("年级：" + grade.getGradeName() + "包括以下班级："); 11 while(iterator.hasNext()) 12 { 13 System.out.println(grade.getGradeName() + ((Class)iterator.next()).getClassName()); 14 } 15 HibernateSessionManager.closeSession(); 16 } 17
18 private static void getSchedule(int gradeid) 19 { 20 Session session = HibernateSessionManager.currentSession(); 21 Transaction transaction = session.beginTransaction(); 22 Grade grade = (Grade)session.get(Grade.class, new Integer(gradeid)); 23 if (grade != null) 24 { 25 System.out.println("ID:" + grade.getGradeID() + "; Name:" + grade.getGradeName()); 26 } 27
28 Hibernate.initialize(grade.getClasses()); 29
30 Iterator iterator = grade.getClasses().iterator(); 31 while(iterator.hasNext()) 32 { 33 Class c = (Class)iterator.next(); 34 System.out.println(grade.getGradeName() + c.getClassName() + "使用以下教室："); 35 Hibernate.initialize(c.getClassrooms()); 36 Iterator iterator1 = c.getClassrooms().iterator(); 37 while(iterator1.hasNext()) 38 { 39 System.out.println(((ClassRoom)iterator1.next()).getClassRoomName()); 40 } 41 } 42 HibernateSessionManager.closeSession(); 43 } 44
45 private static void insertGrade() 46 { 47 Session session = HibernateSessionManager.currentSession(); 48 Transaction transaction = session.beginTransaction(); 49 Grade grade = new Grade(); 50 grade.setGradeID(4); 51 grade.setGradeName("四年级"); 52
53 Class c1 = new Class(); 54 c1.setClassID(7); 55 c1.setGrade(grade); 56 c1.setClassName("一班"); 57 Class c2 = new Class(); 58 c2.setClassID(8); 59 c2.setGrade(grade); 60 c2.setClassName("二班"); 61
62 Set set = new HashSet(); 63 set.add(c1); 64 set.add(c2); 65
66 grade.setClasses(set); 67
68 session.save(grade); 69 session.flush(); 70 transaction.commit(); 71 HibernateSessionManager.closeSession(); 72 getClass(4); 73 } 74
75 private static void deleteGrade(int gradeid) 76 { 77 Session session = HibernateSessionManager.currentSession(); 78 Transaction transaction = session.beginTransaction(); 79 Grade grade = (Grade)session.get(Grade.class, new Integer(gradeid)); 80 if (grade != null) 81 { 82 session.delete(grade); 83 session.flush(); 84 } 85
86 transaction.commit(); 87
88 grade = (Grade)session.get(Grade.class, new Integer(gradeid)); 89 if (grade == null) 90 { 91 System.out.println("删除成功"); 92 } 93 HibernateSessionManager.closeSession(); 94 } 95
96 private static void updateGrade1(int gradeid) 97 { 98 Session session = HibernateSessionManager.currentSession(); 99 Transaction transaction = session.beginTransaction(); 100 Grade grade = (Grade)session.get(Grade.class, new Integer(gradeid)); 101 if (grade != null) 102 { 103 System.out.println("ID:" + grade.getGradeID() + "; Name:" + grade.getGradeName()); 104 } 105 grade.setGradeName("Grade " + gradeid); 106 session.save(grade); 107 session.flush(); 108 transaction.commit(); 109 HibernateSessionManager.closeSession(); 110 getClass(gradeid); 111 } 112
113 private static void updateGrade2(int gradeid) 114 { 115 Session session = HibernateSessionManager.currentSession(); 116 Transaction transaction = session.beginTransaction(); 117 Grade grade = (Grade)session.get(Grade.class, new Integer(gradeid)); 118 if (grade != null) 119 { 120 System.out.println("ID:" + grade.getGradeID() + "; Name:" + grade.getGradeName()); 121 } 122
123 Grade newGrade = new Grade(); 124 newGrade.setGradeID(10); 125 newGrade.setGradeName(grade.getGradeName()); 126 Set set = grade.getClasses(); 127 Set newSet = new HashSet(); 128 Iterator iterator = set.iterator(); 129 while(iterator.hasNext()) 130 { 131 Class c = (Class)iterator.next(); 132 Class temp = new Class(); 133 temp.setClassID(c.getClassID()); 134 temp.setClassName(c.getClassName()); 135 temp.setGrade(newGrade); 136 newSet.add(temp); 137 } 138 newGrade.setClasses(newSet); 139 session.delete(grade); 140 session.flush(); 141 session.save(newGrade); 142 session.flush(); 143 transaction.commit(); 144 grade = (Grade)session.get(Grade.class, new Integer(gradeid)); 145 if (grade == null) 146 { 147 System.out.println("删除成功"); 148 } 149 HibernateSessionManager.closeSession(); 150 getClass(10); 151 }
按顺序调用上面的方法：
1 getClass(1); 2 getSchedule(1); 3 insertGrade(); 4 updateGrade1(4); 5 updateGrade2(4); 6 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：
1 package sample.orm.ibatis; 2
3 import java.io.Serializable; 4
5 public class User implements Serializable 6 { 7 private static final long serialVersionUID = 1L; 8 private int userID; 9 private String userName; 10 public void setUserID(int userID) { 11 this.userID = userID; 12 } 13 public int getUserID() { 14 return userID; 15 } 16 public void setUserName(String userName) { 17 this.userName = userName; 18 } 19 public String getUserName() { 20 return userName; 21 } 22
23 }
然后需要针对这个VO，定义一个独立的配置文件：User.xml
1 <?xml version="1.0" encoding="UTF-8"?>
2 <!DOCTYPE sqlMap 3 PUBLIC "-//iBATIS.com//DTD SQL Map 2.0//EN" 4 "http://www.ibatis.com/dtd/sql-map-2.dtd">
5
6 <sqlMap namespace="User">
7
8 <typeAlias alias="user" type="sample.orm.ibatis.User" />
9
10
11 <cacheModel id="user-cache" type="OSCache" readOnly="true" serialize="true">
12 <flushInterval milliseconds="1" />
13 <flushOnExecute statement="insertUser" />
14 <flushOnExecute statement="updateUser" />
15 <flushOnExecute statement="getUser" />
16 <flushOnExecute statement="getAllUser" />
17 <property value="1" name="size" />
18 </cacheModel>
19
20 <!--
21 <resultMap > 22 <result property="userID" column="id" /> 23 <result property="userName" column="name" /> 24 </resultMap> 25 -->
26
27
28 <select id="getUser" parameterClass="java.lang.Integer" resultClass="user" cacheModel="user-cache" >
29 select id as userID,name as userName from user where id = #userID# 30 </select>
31 <select id="getAllUser" resultClass="user" cacheModel="user-cache">
32 select id as userID,name as userName from user 33 </select>
34 <update id="updateUser" parameterClass="user">
35 update user SET name=#userName# WHERE id = #userID# 36 </update>
37 <insert id="insertUser" parameterClass="user">
38 insert into user ( id, name ) VALUES ( #userID#,#userName#) 39 </insert>
40 <delete id="deleteUser" parameterClass="java.lang.Integer">
41 delete from user where id=#userID# 42 </delete>
43
44 </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：
1 <?xml version="1.0" encoding="UTF-8"?>
2 <!DOCTYPE sqlMapConfig 3 PUBLIC "-//iBATIS.com//DTD SQL Map Config 2.0//EN" 4 "http://www.ibatis.com/dtd/sql-map-config-2.dtd">
5
6 <sqlMapConfig>
7
8 <settings cacheModelsEnabled="true" enhancementEnabled="true"
9 lazyLoadingEnabled="true" errorTracingEnabled="true" maxRequests="32"
10 maxSessions="10" maxTransactions="5" useStatementNamespaces="false" />
11
12 <transactionManager type="JDBC">
13 <dataSource type="SIMPLE">
14 <property name="JDBC.Driver" value="com.mysql.jdbc.Driver" />
15 <property name="JDBC.ConnectionURL" value="jdbc:mysql://localhost/test" />
16 <property name="JDBC.Username" value="root" />
17 <property name="JDBC.Password" value="123" />
18 <property name="Pool.MaximumActiveConnections" value="10" />
19 <property name="Pool.MaximumIdleConnections" value="5" />
20 <property name="Pool.MaximumCheckoutTime" value="120000" />
21 <property name="Pool.TimeToWait" value="500" />
22 <property name="Pool.PingQuery" value="select 1 from user" />
23 <property name="Pool.PingEnabled" value="false" />
24 </dataSource>
25 </transactionManager>
26
27 <sqlMap resource="sample/orm/ibatis/User.xml" />
28
29 </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：
1 public class Sample { 2
3 private SqlMapClient sqlMap = null; 4
5 private void buildMap() throws IOException 6 { 7 String resource = "sample/orm/ibatis/SqlMapConfig.xml"; 8 Reader reader = Resources.getResourceAsReader(resource); 9 this.sqlMap = SqlMapClientBuilder.buildSqlMapClient(reader); 10 } 11
12 private void insertUser() throws IOException, SQLException 13 { 14 System.out.println("=====Insert test====="); 15 if (this.sqlMap == null) 16 { 17 this.buildMap(); 18 } 19 this.sqlMap.startTransaction(); 20 User user = new User(); 21 user.setUserID(10); 22 user.setUserName("Angel"); 23
24 this.sqlMap.insert("insertUser", user); 25 this.sqlMap.commitTransaction(); 26
27 user = getUser(10); 28 printUserInfo(user); 29 } 30
31 private void updateUser() throws IOException, SQLException, InterruptedException 32 { 33 System.out.println("=====Update test====="); 34 if (this.sqlMap == null) 35 { 36 this.buildMap(); 37 } 38 this.sqlMap.startTransaction(); 39 User user = new User(); 40 user.setUserID(10); 41 user.setUserName("Devil"); 42 this.sqlMap.update("updateUser", user); 43 this.sqlMap.commitTransaction(); 44 this.sqlMap.flushDataCache(); 45 // Thread.sleep(3000);
46 user = getUser(10); 47 printUserInfo(user); 48 } 49
50 private void deleteUser() throws IOException, SQLException 51 { 52 System.out.println("=====Delete test====="); 53 if (this.sqlMap == null) 54 { 55 this.buildMap(); 56 } 57 sqlMap.flushDataCache(); 58 this.sqlMap.startTransaction(); 59 this.sqlMap.delete("deleteUser", 10); 60 this.sqlMap.commitTransaction(); 61 getAllUser(); 62 } 63
64 private User getUser(int id) throws IOException, SQLException 65 { 66 if (this.sqlMap == null) 67 { 68 this.buildMap(); 69 } 70 User user = (User)this.sqlMap.openSession().queryForObject("getUser", id); 71
72 return user; 73 } 74
75 private List<User> getAllUser() throws IOException, SQLException 76 { 77 if(this.sqlMap==null) 78 this.buildMap(); 79
80 List userList=null; 81 userList=this.sqlMap.openSession().queryForList("getAllUser"); 82 printUserInfo(userList); 83 return userList; 84 } 85
86 private void printUserInfo(User user) 87 { 88 System.out.println("=====user info====="); 89 System.out.println("ID:" + user.getUserID() + ";Name:" + user.getUserName()); 90 } 91
92 private void printUserInfo(List<User> users) 93 { 94 System.out.println("=====user info====="); 95 for(User user:users) 96 { 97 System.out.println("ID:" + user.getUserID() + ";Name:" + user.getUserName()); 98 } 99 } 100
101 public static void main(String[] args) throws IOException, SQLException, InterruptedException 102 { 103 Sample sample = new Sample(); 104 sample.getAllUser(); 105 sample.insertUser(); 106 sample.updateUser(); 107 sample.deleteUser(); 108 } 109 }
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。