Java中常用的两个ORM框架：Hibernate和iBatis

出处：http://wing011203.cnblogs.com/

http://www.cnblogs.com/wing011203/archive/2013/05/13/3075467.html

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：

定义User对象

　　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.Driverproperty>
 9         <property name="connection.url">jdbc:mysql://localhost/testproperty>
10         <property name="connection.username">rootproperty>
11         <property name="connection.password">123property>    
12         <property name="dialect">org.hibernate.dialect.MySQLDialectproperty>
13         <property name="show_sql">trueproperty>
14         <property name="jdbc.fetch_size">50property>
15         <property name="jdbc.batch_size">25property>
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：

使用Hibernate对user表进行操作

　　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">trueproperty>

　　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：

定义Grade对象

定义Class对象

定义ClassRoom对象

定义Schedule对象

　　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>

　　注意上面的配置，里面的节点说明了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

多表关联情况下的一些测试方法

　　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：

定义User对象

　　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     
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：

iBatis测试方法

　　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。