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

原文地址：http://blog.csdn.net/xqf309/article/details/27721777

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：

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<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

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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;

}

}

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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：

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<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>

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<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：

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<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：

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<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

...

思路三：由数据库表（或DDL）生成POJO类和hbm.xml

...

思路二三请见下一博客！

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