HibernateTools实现pojo类 数据库schma mapping映射的相互转换

核心

利用HibernateTools，从POJO类，Mapping映射文件，数据库表有其中的一项，就能生成其他两项。

概述

在使用Hibernate开发系统持久层时，按照一般开发流程

 

1、分析业务

2、获得系统实体类

3、写Hibernate的mapping映射文件

4、根据映射文件，生成数据库表

 

    以上这几步是Hibernate开发的起始。根据开发习惯的不同，有些项目组可能会先写POJO类，有的项目可能会先设计数据库，有的项目组可能先写映射文件，其实完成其中的一项时，类结构或者表结构就可以确定了。

既然已经能确定结构了，完全可以使用工具来代替手工完成剩余的工作。

前提

    安装Eclipse插件HibernateTools，eclipse插件安装百度下教程非常多，建议采用copy安装或者link安装，再有就是HibernateTools的版本对应着特定的Eclipse版本，所以安装前请先检查自己的eclipse版本。

   然后建立项目，本文建立的是Dynamic Web Project，采用了mysql数据库，建立项目后，引入mysql的驱动jar，引入Hibernate（本文用了4.3.5版本）的包，即lib下required文件夹中所有jar

   安装完了插件，首先利用tool生成Hibernate配置文件，项目右键-->new，安装完HibernateTools后，多了4种类型的文件，选择第一种：

根据使用的数据库，填入必须的属性：

生成hibernate.cfg.xml的代码：

<span style="font-family:KaiTi_GB2312;font-size:18px;"><?xml version="1.0" encoding="utf-8"?>  
<!DOCTYPE hibernate-configuration PUBLIC  
"-//Hibernate/Hibernate Configuration DTD 3.0//EN"  
"http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">  
<hibernate-configuration>  
    <session-factory>  
        <property name="hibernate.bytecode.use_reflection_optimizer">false</property>  
        <property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>  
        <property name="hibernate.connection.password">123456</property>  
        <property name="hibernate.connection.url">jdbc:mysql://localhost:3306/test</property>  
        <property name="hibernate.connection.username">root</property>  
        <property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>  
        <property name="hibernate.search.autoregister_listeners">false</property>  
         
          
    </session-factory>  
</hibernate-configuration></span>  

相互转换

接下可以进入正题了，本文分别从三项中的每一项入手，生成其他两项。 

思路一：由POJO类生成mapping映射文件和DDL

POJO类的代码写起来非常方便，因此首先介绍这种方法，个人认为这种方法效率最高。首先建立两个POJO类

package org.hibernate.test;  
  
  
public class Student implements java.io.Serializable {  
  
    private int id;  
    private String name;  
  
    public Student() {  
    }  
  
    public Student(int id) {  
        this.id = id;  
    }  
  
    public Student(int id, String name) {  
        this.id = id;  
        this.name = name;  
    }  
  
    public int getId() {  
        return this.id;  
    }  
  
    public void setId(int id) {  
        this.id = id;  
    }  
  
    public String getName() {  
        return this.name;  
    }  
  
    public void setName(String name) {  
        this.name = name;  
    }  
  
}  

package org.hibernate.test;  
  
  
import java.util.ArrayList;  
import java.util.List;  
  
  
public class Class implements java.io.Serializable {  
  
    private int id;  
    private String name;  
    private List students = new ArrayList(0);  
  
    public Class() {  
    }  
  
    public Class(int id) {  
        this.id = id;  
    }  
  
    public Class(int id, String name, List students) {  
        this.id = id;  
        this.name = name;  
        this.students = students;  
    }  
  
    public int getId() {  
        return this.id;  
    }  
  
    public void setId(int id) {  
        this.id = id;  
    }  
  
    public String getName() {  
        return this.name;  
    }  
  
    public void setName(String name) {  
        this.name = name;  
    }  
  
    public List getStudents() {  
        return this.students;  
    }  
  
    public void setStudents(List students) {  
        this.students = students;  
    }  
  
}  

接下来一步一步生成另外两项，首先项目右键-->new,选择Hibernate下面的第四项，建立mapping映射文件，根据已存在的POJO类，生成Mapping文件

添加两个已经存在的POJO类

下一步，可以预先查看生成的hbm.xml文件，有特殊要求的可以再生成的文件基础上稍作修改。

生成代码：

<span style="font-family:KaiTi_GB2312;font-size:18px;"><?xml version="1.0"?>  
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"  
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">  
<!-- Generated 2014-5-30 21:29:20 by Hibernate Tools 4.0.0 -->  
<hibernate-mapping>  
    <class name="org.hibernate.test.Student" table="STUDENT">  
        <id name="id" type="int">  
            <column name="ID" />  
            <generator class="assigned"></generator>  
        </id>  
        <property name="name" type="java.lang.String">  
            <column name="NAME" />  
        </property>  
    </class>  
</hibernate-mapping></span>  

<span style="font-family:KaiTi_GB2312;font-size:18px;"><?xml version="1.0"?>  
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"  
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">  
<!-- Generated 2014-5-30 21:29:20 by Hibernate Tools 4.0.0 -->  
<hibernate-mapping>  
    <class name="org.hibernate.test.Class" table="CLASS">  
        <id name="id" type="int">  
            <column name="ID" />  
            <generator class="assigned"></generator>  
        </id>  
        <property name="name" type="java.lang.String">  
            <column name="NAME" />  
        </property>  
        <list name="students" inverse="false" table="STUDENT" lazy="true">  
            <key>  
                <column name="ID" />  
            </key>  
            <list-index>  
                <column name="idx" />  
            </list-index>  
            <one-to-many class="org.hibernate.test.Student" />  
        </list>  
    </class>  
</hibernate-mapping></span>  

mapping映射文件生成了，接下来生成ddl，项目右键-->new，选择Hibernate Console  Configuration

选择好对应的项后，finish，然后需要在工具栏添加Hibernate code Generation，Windows-->Customer Perspective

然后工具栏多了一个很像运行按钮的图标，单击下拉按钮，选第二项

单击Exporters选项卡，可以看到HibernateTools工具能导出和生成的项很多，可以根据配置有针对性的选择自己想要的项，这里我们勾选Schema Export，然后单击图标1下面的Properties的Add，后出现图标2所示的窗体

选择第二项，这就是要生成我们想要的ddl，如图，当然上图还勾选了DAO Code，生成了操作试题的DAO代码（HibernateTools确实很贴心）

这是生成后的图片

ddl的建表语句：

<span style="font-family:KaiTi_GB2312;font-size:18px;">create table CLASS (ID integer not null, NAME varchar(255), primary key (ID));  
create table STUDENT (ID integer not null, NAME varchar(255), idx integer, primary key (ID));  
alter table STUDENT add index FKBACA0E1BE081A5FD (ID), add constraint FKBACA0E1BE081A5FD foreign key (ID) references CLASS (ID);  
</span>  

DAO代码如下：

<span style="font-family:KaiTi_GB2312;font-size:18px;">package org.hibernate.test;  
  
// Generated 2014-5-30 23:18:05 by Hibernate Tools 4.0.0  
  
import java.util.List;  
import javax.naming.InitialContext;  
import org.apache.commons.logging.Log;  
import org.apache.commons.logging.LogFactory;  
import org.hibernate.LockMode;  
import org.hibernate.SessionFactory;  
import org.hibernate.criterion.Example;  
  
/**  
 * Home object for domain model class Class.  
 * @see org.hibernate.test.Class  
 * @author Hibernate Tools  
 */  
public class ClassHome {  
  
    private static final Log log = LogFactory.getLog(ClassHome.class);  
  
    private final SessionFactory sessionFactory = getSessionFactory();  
  
    protected SessionFactory getSessionFactory() {  
        try {  
            return (SessionFactory) new InitialContext()  
                    .lookup("SessionFactory");  
        } catch (Exception e) {  
            log.error("Could not locate SessionFactory in JNDI", e);  
            throw new IllegalStateException(  
                    "Could not locate SessionFactory in JNDI");  
        }  
    }  
  
    public void persist(Class transientInstance) {  
        log.debug("persisting Class instance");  
        try {  
            sessionFactory.getCurrentSession().persist(transientInstance);  
            log.debug("persist successful");  
        } catch (RuntimeException re) {  
            log.error("persist failed", re);  
            throw re;  
        }  
    }  
  
    public void attachDirty(Class instance) {  
        log.debug("attaching dirty Class instance");  
        try {  
            sessionFactory.getCurrentSession().saveOrUpdate(instance);  
            log.debug("attach successful");  
        } catch (RuntimeException re) {  
            log.error("attach failed", re);  
            throw re;  
        }  
    }  
  
    public void attachClean(Class instance) {  
        log.debug("attaching clean Class instance");  
        try {  
            sessionFactory.getCurrentSession().lock(instance, LockMode.NONE);  
            log.debug("attach successful");  
        } catch (RuntimeException re) {  
            log.error("attach failed", re);  
            throw re;  
        }  
    }  
  
    public void delete(Class persistentInstance) {  
        log.debug("deleting Class instance");  
        try {  
            sessionFactory.getCurrentSession().delete(persistentInstance);  
            log.debug("delete successful");  
        } catch (RuntimeException re) {  
            log.error("delete failed", re);  
            throw re;  
        }  
    }  
  
    public Class merge(Class detachedInstance) {  
        log.debug("merging Class instance");  
        try {  
            Class result = (Class) sessionFactory.getCurrentSession().merge(  
                    detachedInstance);  
            log.debug("merge successful");  
            return result;  
        } catch (RuntimeException re) {  
            log.error("merge failed", re);  
            throw re;  
        }  
    }  
  
    public Class findById(int id) {  
        log.debug("getting Class instance with id: " + id);  
        try {  
            Class instance = (Class) sessionFactory.getCurrentSession().get(  
                    "org.hibernate.test.Class", id);  
            if (instance == null) {  
                log.debug("get successful, no instance found");  
            } else {  
                log.debug("get successful, instance found");  
            }  
            return instance;  
        } catch (RuntimeException re) {  
            log.error("get failed", re);  
            throw re;  
        }  
    }  
  
    public List findByExample(Class instance) {  
        log.debug("finding Class instance by example");  
        try {  
            List results = sessionFactory.getCurrentSession()  
                    .createCriteria("org.hibernate.test.Class")  
                    .add(Example.create(instance)).list();  
            log.debug("find by example successful, result size: "  
                    + results.size());  
            return results;  
        } catch (RuntimeException re) {  
            log.error("find by example failed", re);  
            throw re;  
        }  
    }  
}</span>  

到此，我们就由POJO类，生成了hbm.xml文件和DDL

思路二：由hbm.xml生成POJO类和DDL...

虽然可以实现，但个人觉着先设计数据库，然后再生成类不符合Hibernate的面对对象持久化的思维方式。好了，还是说步骤吧，首先在test数据库建立两张表，分别为course表和teacher表

[sql] view plain copy
-- ----------------------------  
-- Table structure for course  
-- ----------------------------  
DROP TABLE IF EXISTS `course`;  
CREATE TABLE `course` (  
  `id` int(11) NOT NULL,  
  `name` varchar(255) DEFAULT NULL,  
  PRIMARY KEY (`id`)  
) ENGINE=InnoDB DEFAULT CHARSET=utf8;  
  
-- ----------------------------  
-- Table structure for teacher  
-- ----------------------------  
DROP TABLE IF EXISTS `teacher`;  
CREATE TABLE `teacher` (  
  `id` int(11) NOT NULL,  
  `name` varchar(255) DEFAULT NULL,  
  PRIMARY KEY (`id`)  
) ENGINE=InnoDB DEFAULT CHARSET=utf8;  

建好表后，在eclipse项目上右键-->new,如下图，选择框中的第三项，这个reveng.xml文件用于配置 选择要生成POJO类的数据库表。

选择上篇博客中创建的Console configuration项，点Database schema框下的refresh，之后可以看到test数据库，单击就出现了course和teacher表，全选后点击Include,之后点finish，如下图

再来到Hibernate Code Generation Configuration窗体，首先配置下Output directory输出目录，在尽挨着的复选框打上勾，然后在package栏写上生成文件要输出到哪个包，并选择刚配置好的reveng.xml文件

配置要输出的项，这里选定前两项，生成.java和.hbm.xml，就是我们想要的POJO类和Mapping映射文件。之后点击run就好了。

结果如下图：

生成的Mapping映射文件的代码

<?xml version="1.0"?>  
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"  
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">  
<!-- Generated 2014-5-31 11:19:19 by Hibernate Tools 4.0.0 -->  
<hibernate-mapping>  
    <class name="org.hibernate.test.Course" table="course" catalog="test">  
        <id name="id" type="int">  
            <column name="id" />  
            <generator class="assigned" />  
        </id>  
        <many-to-one name="teacher" class="org.hibernate.test.Teacher" fetch="select">  
            <column name="teacherId" not-null="true" />  
        </many-to-one>  
        <property name="name" type="string">  
            <column name="name" />  
        </property>  
    </class>  
</hibernate-mapping>  

<?xml version="1.0"?>  
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"  
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">  
<!-- Generated 2014-5-31 11:19:19 by Hibernate Tools 4.0.0 -->  
<hibernate-mapping>  
    <class name="org.hibernate.test.Teacher" table="teacher" catalog="test">  
        <id name="id" type="int">  
            <column name="id" />  
            <generator class="assigned" />  
        </id>  
        <property name="name" type="string">  
            <column name="name" />  
        </property>  
        <set name="courses" table="course" inverse="true" lazy="true" fetch="select">  
            <key>  
                <column name="teacherId" not-null="true" />  
            </key>  
            <one-to-many class="org.hibernate.test.Course" />  
        </set>  
    </class>  
</hibernate-mapping>  

生成的POJO类：

package org.hibernate.test;  
  
// Generated 2014-5-31 11:19:19 by Hibernate Tools 4.0.0  
  
/** 
 * Course generated by hbm2java 
 */  
public class Course implements java.io.Serializable {  
  
    private int id;  
    private Teacher teacher;  
    private String name;  
  
    public Course() {  
    }  
  
    public Course(int id, Teacher teacher) {  
        this.id = id;  
        this.teacher = teacher;  
    }  
  
    public Course(int id, Teacher teacher, String name) {  
        this.id = id;  
        this.teacher = teacher;  
        this.name = name;  
    }  
  
    public int getId() {  
        return this.id;  
    }  
  
    public void setId(int id) {  
        this.id = id;  
    }  
  
    public Teacher getTeacher() {  
        return this.teacher;  
    }  
  
    public void setTeacher(Teacher teacher) {  
        this.teacher = teacher;  
    }  
  
    public String getName() {  
        return this.name;  
    }  
  
    public void setName(String name) {  
        this.name = name;  
    }  
  
}  

package org.hibernate.test;  
  
// Generated 2014-5-31 11:19:19 by Hibernate Tools 4.0.0  
  
import java.util.HashSet;  
import java.util.Set;  
  
/** 
 * Teacher generated by hbm2java 
 */  
public class Teacher implements java.io.Serializable {  
  
    private int id;  
    private String name;  
    private Set courses = new HashSet(0);  
  
    public Teacher() {  
    }  
  
    public Teacher(int id) {  
        this.id = id;  
    }  
  
    public Teacher(int id, String name, Set courses) {  
        this.id = id;  
        this.name = name;  
        this.courses = courses;  
    }  
  
    public int getId() {  
        return this.id;  
    }  
  
    public void setId(int id) {  
        this.id = id;  
    }  
  
    public String getName() {  
        return this.name;  
    }  
  
    public void setName(String name) {  
        this.name = name;  
    }  
  
    public Set getCourses() {  
        return this.courses;  
    }  
  
    public void setCourses(Set courses) {  
        this.courses = courses;  
    }  
  
}  

到此我们就完成了由数据库表生成POJO类和Mapping映射文件的过程

思路三：由数据库表（或DDL）生成POJO类和hbm.xml

首先，新建一个Mapping文件，这里在项目中建立Department.hbm.xml。

<?xml version="1.0" encoding="UTF-8"?>  
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd" >  
<hibernate-mapping>  
    <class name="org.hibernate.test.Department" table="DEPARTMENT">  
        <id name="id" type="int">  
            <column name="ID" />  
            <generator class="increment"></generator>  
        </id>  
        <property name="name" type="java.lang.String">  
            <column name="NAME" />  
        </property>  
    </class>  
</hibernate-mapping>  

接下来建一个新的Console Configuration文件，基本配置和上文中配置的过程一样，最关键的是加入mapping文件。

接下来，改下Hibernate Code Generation Configuration就好了，首选选择新配置的Console Configuration文件

接下来选择要生成的Schema和.Java文件，然后run就可以了。

最终结果如图：

生成的DDL代码为

[sql] view plain copy
create table DEPARTMENT (ID integer not null, NAME varchar(255), primary key (ID));</span>  

POJO类：

package org.hibernate.test;  
  
// Generated 2014-5-31 16:23:27 by Hibernate Tools 4.0.0  
  
/** 
 * Department generated by hbm2java 
 */  
public class Department implements java.io.Serializable {  
  
    private int id;  
    private String name;  
  
    public Department() {  
    }  
  
    public Department(String name) {  
        this.name = name;  
    }  
  
    public int getId() {  
        return this.id;  
    }  
  
    public void setId(int id) {  
        this.id = id;  
    }  
  
    public String getName() {  
        return this.name;  
    }  
  
    public void setName(String name) {  
        this.name = name;  
    }  
  
}  

好了，至此POJO类，Mapping文件和数据库表相互转化就都介绍完了，当然这是借助eclipse的插件实现的，熟悉使用ant的朋友也可以借助ant脚本来实现，具体的教程去google吧。这里推荐下HibernateTools的官方教程，包含了eclipse插件和ant脚本两种实现方式，非常全面。