Hello,World in Hibernate 入门

url:
http://www.blogjava.net/zhuguangxiang/archive/2007/02/10/99147.html

本文介绍如何用hibernate写一个hello world 程序，以及说明Hibernate下的对象的识别。
1、配置文件hibernate.cfg.xml：

<? xml version = ' 1.0 '  encoding = ' utf-8 ' ?>
<! DOCTYPE hibernate - configuration PUBLIC
         " -//Hibernate/Hibernate Configuration DTD 3.0//EN "
         " http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd " >

< hibernate - configuration >

     < session - factory >

         <!--  Database connection settings  -->
         < property name = " connection.driver_class " > com.mysql.jdbc.Driver </ property >
         < property name = " connection.url " > jdbc:mysql: // localhost:3306/eg</property>
          < property name = " connection.username " > root </ property >
         < property name = " connection.password " > 4864452 </ property >

         <!--  JDBC connection pool (use the built - in)  -->
         < property name = " connection.pool_size " > 1 </ property >

         <!--  SQL dialect  -->
         < property name = " dialect " > org.hibernate.dialect.MySQLInnoDBDialect </ property >

         <!--  Enable Hibernate ' s automatic session context management -->
          < property name = " current_session_context_class " > thread </ property >

         <!--  Disable the second - level cache   -->
         < property name = " cache.provider_class " > org.hibernate.cache.NoCacheProvider </ property >

         <!--  Echo all executed SQL to stdout  -->
         < property name = " show_sql " > true </ property >

         <!--  Drop and re - create the database schema on startup
         < property name = " hbm2ddl.auto " > create </ property >
          -->
   
         < mapping resource = " eg/Message.hbm.xml " />
       
       
     </ session - factory >

</ hibernate - configuration >
2、源文件：

package  eg;

public   class  Message   {
     private  Long id;
     private  String text;
            
     private  Message nextMessage;

     public  Message()   {}
      public  Message(String text)  {
         this .text = text;
    }
   
     public   void  setId(Long id)   {
         this .id  =  id;
    }

      public   void  setText(String text)   {
         this .text  =  text;
    }

      public   void  setNextMessage(Message nextMessage)   {
         this .nextMessage  =  nextMessage;
    }
         public  Long getId()   {
         return  ( this .id);
    }
         public  String getText()   {
         return  ( this .text);
    }
         public  Message getNextMessage()   {
         return  ( this .nextMessage);
    } 
}

3、配置文件：Messsage.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 =" eg.Message "
        table = " MESSAGE "
     >

         < id
            name = " id "
            column = " MESSAGE_ID "
            type = " java.lang.Long "
         >
             < generator  class = " native " />
                        
         </ id >
         < property
            name = " text "
            type = " java.lang.String "
            update = " true "
            insert = " true "
            column = " MESSAGE_TEXT "
         />

         < many - to - one
            name = " nextMessage "
             class = " jmuse.eg.Message "
            cascade = " all "
            outer - join = " auto "
            update = " true "
            insert = " true "
            column = " NEXT_MESSAGE_ID "
         />

       </ class >

</ hibernate - mapping >

4、最后的包结构：


+ lib
     antlr.jar
     cglib.jar
     asm.jar
     asm - attrs.jars
     commons - collections.jar
     commons - logging.jar
     hibernate3.jar
     jta.jar
     dom4j.jar
     log4j.jar
＋src
     + eg
       Message.java
       Message.hbm.xml
       TestMessage.java
     hibernate.cfg.ml
     log4j.properties

5、测试：

  session.beginTransaction();
        Message m = new  Message( " hello,world " );
        session.save(m);
        session.getTransaction().commit();
        session.close();

你会发现在数据库中有一条信息了，id=1
Hibernate的对象识别是通过对象的Id 来识别的：
如：


我们刚才在数据库中保存了一个Id为1的Message对象。
如果：
session.beginTraction();
Message m = new  Message();
m.setId( new  Long( 1 ));
m.setText( " This is another greeting " );
session.saveOrUpdate(m);
sesion.getTraction.commit();
你会发现Hibernate会自动的把刚才的对象进行更新，而不是保存一个新的对象。
这个例子有点极端，呵呵。能说明问题就可以了。