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Hello,World in Hibernate 入门

Posted on 2010-05-04 11:30 無所謂 阅读(366) 评论(1)  编辑  收藏 所属分类: Hibernate

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。

评论

# re: Hello,World in Hibernate 入门   回复  更多评论   

2012-05-17 09:44 by hqan
看不懂，也运行不起来，没说清楚原理。

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