Java回顾之ORM框架

淡淡的烟草味﹌ 2022-06-07 08:59 173阅读 0赞

## 1. 什么是ORM? ##

对象-关系映射（Object-Relational Mapping，简称ORM），面向对象的开发方法是当今企业级应用开发环境中的主流开发方法，关系数据库是企业级应用环境中永久存放数据的主流数据存储系统。对象和关系数据是业务实体的两种表现形式，业务实体在内存中表现为对象，在数据库中表现为关系数据。内存中的对象之间存在关联和继承关系，而在数据库中，关系数据无法直接表达多对多关联和继承关系。因此，对象-关系映射(ORM)系统一般以中间件的形式存在，主要实现程序对象到关系数据库数据的映射。

## 2.为什么使用ORM? ##

当我们实现一个应用程序时（不使用O/R Mapping），我们可能会写特别多数据访问层的代码，从数据库保存、删除、读取对象信息，而这些代码都是重复的。而使用ORM则会大大减少重复性代码。对象关系映射（Object Relational Mapping，简称ORM），主要实现程序对象到关系数据库数据的映射。

## 3.对象-关系映射解释： ##

A . 简单：ORM以最基本的形式建模数据。比如ORM会将MySQL的一张表映射成一个java类（模型），表的字段就是这个类的成员变量   
B . 精确：ORM使所有的MySQL数据表都按照统一的标准精确地映射成java类，使系统在代码层面保持准确统一   
C .易懂：ORM使数据库结构文档化。比如MySQL数据库就被ORM转换为了java程序员可以读懂的java类，java程序员可以只把注意力放在他擅长的java层面（当然能够熟练掌握MySQL更好）   
D.易用：ORM包含对持久类对象进行CRUD操作的API，例如create(), update(), save(), load(), find(), find\_all(), where()等，也就是讲sql查询全部封装成了编程语言中的函数，通过函数的链式组合生成最终的SQL语句。通过这种封装避免了不规范、冗余、风格不统一的SQL语句，可以避免很多人为Bug，方便编码风格的统一和后期维护。   
![这里写图片描述][20160307142645476]

## 4. ORM的优缺点： ##

优点：   
提高开发效率，降低开发成本   
使开发更加对象化   
可移植   
可以很方便地引入数据缓存之类的附加功能   
缺点：   
自动化进行关系数据库的映射需要消耗系统性能。其实这里的性能消耗还好啦，一般来说都可以忽略之。

在处理多表联查、where条件复杂之类的查询时，ORM的语法会变得复杂。

## 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。

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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 }

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### 　　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][Java_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：

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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 }

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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。

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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。

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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>

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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：

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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 }

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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：

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=====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.

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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：

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：

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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 }

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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 }

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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 }

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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 }

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接着是各个表的关联配置文件：

1）Grade.hbm.xml

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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>

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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

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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>

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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

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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>

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它只定义了一个关联：和Class之间的多对多关联。

4）Schedule.hbm.xml

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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>

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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

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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 }

![复制代码][copycode.gif]

按顺序调用上面的方法：

![复制代码][copycode.gif]

1 getClass(1); 2 getSchedule(1); 3 insertGrade(); 4 updateGrade1(4); 5 updateGrade2(4); 6 deleteGrade(10);

![复制代码][copycode.gif]

执行结果如下：

![复制代码][copycode.gif]

=====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

![复制代码][copycode.gif]

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：

![复制代码][copycode.gif]

![ExpandedBlockStart.gif][]

![复制代码][copycode.gif]

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 }

![复制代码][copycode.gif]

然后需要针对这个VO，定义一个独立的配置文件：User.xml

![复制代码][copycode.gif]

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>

![复制代码][copycode.gif]

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：

![复制代码][copycode.gif]

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>

![复制代码][copycode.gif]

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：

![复制代码][copycode.gif]

![ExpandedBlockStart.gif][]

![复制代码][copycode.gif]

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 }

![复制代码][copycode.gif]

它的执行结果如下：

![复制代码][copycode.gif]

=====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

![复制代码][copycode.gif]

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。

[20160307142645476]: /images/20220607/a159a6662bd64d53b01b17ba7ebec862.png
[copycode.gif]: /images/20220607/f9b8ce7208d04d93868a4b2b0d01e7d3.png
[ExpandedBlockStart.gif]: /images/20220607/70c67d9cab764d39a2042531840f1f1a.png
[Java_JDBC]: http://www.cnblogs.com/wing011203/archive/2013/05/12/3073838.html