基于XDoclet的Hibernate3企业级开发教程（1）——one2one映射类型的书写要点

基于XDoclet的Hibernate3企业级开发教程（1）——one2one映射类型的书写要点

摘要：此为我给公司内部新员工培训的实战演示例子，傻瓜级教程，讲述了开发中的注意要点和常见错误，目的主要是让他们适应企业级快速流水作业。由于是面对面讲解，所以没有详细的文档，现在简单整理如下，希望对入门者有帮助。

培训的目标：对下面的开发过程和模式快速理解和应用。基于我的UML架构-----〉Java POJOs代码------〉在pojos中做xdoclet标识-------〉基于ant生成*.hbm.xml文件（借助于eclipse可以自动化配置）------〉生成database schma和数据库sql语句。逐步可以让新员工过渡到java5的annotation来开发EJB3 .

基于主键的一对一关联映射

说明：下面是我们用到的例子，学生和自己学籍上的照片是一对一关系。下面是使用IBM RSA得到的一个模型，途中用的是两个用途，表示的意思比较泛，最佳表示应该是一条无方向的线段，两边各标上1，代表一对一关系。（现在时间比较紧，所以没来的急修改，这也是IBM反向工程的一个弱点，就好比目标是北京，但是现在目标指向了中国，不够精确,但是可以反映这个意思）

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下面是生成的数据库E-R图：

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问题：初学者总是对pojos对象中的字段和数据库中的字段做对比，对pojos对象中多出的propertity感到不解，其实这也是hibernate的关键所在，在那个表增加字段，增加外键，都是有规律的，也是完全符合数据库的规则的，详细看代码.

初学者应该注意点，需要自己进行实践的操作：

1， /**
*@hibernate.classtable="image"schema="hibernate_tutorial"
*@authorAdministrator
*
*/

schema对mysql数据库来说，是数据库名字，这点注意

2， 你可以在关联属性上都定义外键，你看一下最后那边的设置在数据库sql语句中体现了，那个没体现，我想你会有收获的。

3， /**
*@hibernate.one-to-oneclass="com.javawebside.one2one.p1.Image"
*constrained="false"outer-join="true"cascade="all"
*@returnReturnstheimage.
*/
注意cascade的设置，如果没有级联，那么你可以最后save student,或者save image，或者，两者都保存，你看一下数据库中实际存入的数据，你一定会对cascade有更加深入的认识。

Image类

packagecom.javawebside.one2one.p1;

importjava.sql.Blob;
/**
*@hibernate.classtable="image"schema="hibernate_tutorial"
*@authorAdministrator
*
*/
publicclassImage{

privateLongid;

privateStringname;

privateBlobvalue=null;


/**
*@linkassociation
*/

privateStudentstudent;

publicImage(){}
publicImage(Longid,Stringname,Blobvalue){
super();
this.id=id;
this.name=name;
this.value=value;
}

/**
*@hibernate.idcolumn="id"generator-class="foreign"
*@hibernate.generator-paramname="property"value="student"
*@returnReturnstheid.
*/
publicLonggetId(){
returnid;
}

/**
*@paramid
*Theidtoset.
*/
publicvoidsetId(Longid){
this.id=id;
}

/**
*@hibernate.propertycolumn="name"not-null="false"unique="false"
*@returnReturnsthename.
*/
publicStringgetName(){
returnname;
}

/**
*@paramname
*Thenametoset.
*/
publicvoidsetName(Stringname){
this.name=name;
}

/**
*@hibernate.propertycolumn="value"not-null="false"unique="false"
*@returnReturnsthevalue.
*/
publicBlobgetValue(){
returnvalue;
}

/**
*@paramvalue
*Thevaluetoset.
*/
publicvoidsetValue(Blobvalue){
this.value=value;
}

/**
*@hibernate.one-to-oneclass="com.javawebside.one2one.p1.Student"constrained="true"
*foreign-key="forein_key_name"
*@return
*/
publicStudentgetStudent(){
returnstudent;
}

publicvoidsetStudent(Studentstudent){
this.student=student;
}

}

Student类

packagecom.javawebside.one2one.p1;

/**
*
*@hibernate.classtable="student"schema="hibernate_tutorial"
*@authorAdministrator
*
*/
publicclassStudent{

privateLongid;

privateStringname;

privateStringintro;

privateImageimage;



publicStudent(){
}

publicStudent(Longid,Stringname,Stringintro,Imageimage){
super();
this.id=id;
this.name=name;
this.intro=intro;
this.image=image;
}

/**
*@hibernate.idcolumn="id"generator-class="native"
*@returnReturnstheid.
*/
publicLonggetId(){
returnid;
}

/**
*@paramid
*Theidtoset.
*/
publicvoidsetId(Longid){
this.id=id;
}

/**
*@hibernate.propertycolumn="intro"not-null="false"unique="false"
*@returnReturnstheintro.
*/
publicStringgetIntro(){
returnintro;
}

/**
*@paramintro
*Theintrotoset.
*/
publicvoidsetIntro(Stringintro){
this.intro=intro;
}

/**
*@hibernate.propertycolumn="name"not-null="false"unique="false"
*@returnReturnsthename.
*/
publicStringgetName(){
returnname;
}

/**
*@paramname
*Thenametoset.
*/
publicvoidsetName(Stringname){
this.name=name;
}

/**
*@hibernate.one-to-oneclass="com.javawebside.one2one.p1.Image"
*constrained="false"outer-join="true"cascade="all"
*@returnReturnstheimage.
*/
publicImagegetImage(){
returnimage;
}

/**
*@paramimage
*Theimagetoset.
*/
publicvoidsetImage(Imageimage){
this.image=image;
}

}

下面是实际的操作类

BusinessService类用于增加和删除数据操作

packagecom.javawebside.one2one.p1;

importjava.sql.Blob;
importorg.hibernate.*;
//importorg.hibernate.cfg.Configuration;

//importjava.util.*;

publicclassBusinessService{
privateSessionsession;

publicvoidsetSession(Sessionse){
session=se;
}

publicSessiongetSession(){
returnsession;
}

publicvoidsaveStudent(StudentStudent)throwsException{
Transactiontx=null;
try{
tx=session.beginTransaction();
session.save(Student);
tx.commit();

}catch(Exceptione){
if(tx!=null){
tx.rollback();
}
throwe;
}finally{
//Nomatterwhat,closethesession
session.close();
}
}

publicStudentloadStudent(Longid)throwsException{
Transactiontx=null;
try{
tx=session.beginTransaction();
StudentStudent=(Student)session.load(Student.class,id);
tx.commit();

returnStudent;

}catch(Exceptione){
if(tx!=null){
tx.rollback();
}
throwe;
}finally{
//Nomatterwhat,closethesession
session.close();
}
}

publicvoidprintStudent(StudentStudent)throwsException{
Imageimage=Student.getImage();
System.out.println("Imageof"+Student.getName()+"is:"
+image.getValue());

if(image.getStudent()==null)
System.out.println("CannotnaviagtefromImagetoStudent.");
}

publicvoidtest()throwsException{

Studentstudent=newStudent();
Imageimage=newImage();
image.setName("王东照片");

student.setName("Tom");
student.setIntro("王东");

image.setStudent(student);
student.setImage(image);

saveStudent(student);

//student=loadStudent(student.getId());
//printStudent(student);

}

publicstaticvoidmain(Stringargs[])throwsException{
BusinessServicebs=newBusinessService();
bs.setSession(HibernateSessionFactory.currentSession());
if(bs.getSession()==null)
System.out.println("Sessionisnull");
bs.test();
//bs.getSession().close();
}
}

hibernate配置类

packagecom.javawebside.one2one.p1;

importorg.hibernate.HibernateException;
importorg.hibernate.Session;
importorg.hibernate.cfg.Configuration;

/**
*ConfiguresandprovidesaccesstoHibernatesessions,tiedtothe
*currentthreadofexecution.FollowstheThreadLocalSession
*pattern,see{@linkhttp://hibernate.org/42.html}.
*/
publicclassHibernateSessionFactory{

/**
*Locationofhibernate.cfg.xmlfile.
*NOTICE:LocationshouldbeontheclasspathasHibernateuses
*#resourceAsStreamstylelookupforitsconfigurationfile.That
*isplacetheconfigfileinaJavapackage-thedefaultlocation
*isthedefaultJavapackage.<br><br>
*Examples:<br>
*<code>CONFIG_FILE_LOCATION="/hibernate.conf.xml".
*CONFIG_FILE_LOCATION="/com/foo/bar/myhiberstuff.conf.xml".</code>
*/
privatestaticStringCONFIG_FILE_LOCATION="com/javawebside/one2one/p1/hibernate.cfg.xml";

/**HoldsasingleinstanceofSession*/
privatestaticfinalThreadLocal<Session>threadLocal=newThreadLocal<Session>();

/**Thesingleinstanceofhibernateconfiguration*/
privatestaticfinalConfigurationcfg=newConfiguration();

/**ThesingleinstanceofhibernateSessionFactory*/
privatestaticorg.hibernate.SessionFactorysessionFactory;

/**
*ReturnstheThreadLocalSessioninstance.Lazyinitialize
*the<code>SessionFactory</code>ifneeded.
*
*@returnSession
*@throwsHibernateException
*/
publicstaticSessioncurrentSession()throwsHibernateException{
Sessionsession=(Session)threadLocal.get();

if(session==null||!session.isOpen()){
if(sessionFactory==null){
try{
cfg.configure(CONFIG_FILE_LOCATION);
sessionFactory=cfg.buildSessionFactory();
}catch(Exceptione){
System.err
.println("%%%%ErrorCreatingSessionFactory%%%%");
e.printStackTrace();
}
}
session=(sessionFactory!=null)?sessionFactory.openSession()
:null;
threadLocal.set(session);
}

returnsession;
}

/**
*Closethesinglehibernatesessioninstance.
*
*@throwsHibernateException
*/
publicstaticvoidcloseSession()throwsHibernateException{
Sessionsession=(Session)threadLocal.get();
threadLocal.set(null);

if(session!=null){
session.close();
}
}

/**
*Defaultconstructor.
*/
privateHibernateSessionFactory(){
}

}