Hibernate入门

Posted 2020-06-20 Season

1，安装

     从官网下载hibernate-release-5.1.0.Final.zip，解压后把lib\required目录下jar包全部添加到MyEclipse项目Build Path中

2，源码清单

 Event.java

package com.bf;

import java.util.Date;

public class Event {
    private Long id;

    private String title;
    private Date date;

    public Event() {
        // this form used by Hibernate
    }

    public Event(String title, Date date) {
        // for application use, to create new events
        this.title = title;
        this.date = date;
    }

    public Long getId() {
        return id;
    }

    private void setId(Long id) {
        this.id = id;
    }

    public Date getDate() {
        return date;
    }

    public void setDate(Date date) {
        this.date = date;
    }

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }
}

Event.hbm.xml

<?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">

<hibernate-mapping package="com.bf">

    <class name="Event" table="EVENTS">
        <id name="id" column="EVENT_ID">
            <generator class="increment"/>
        </id>
        <property name="date" type="timestamp" column="EVENT_DATE"/>
        <property name="title"/>
    </class>

</hibernate-mapping>

hibernate.cfg.xml

<?xml version=‘1.0‘ encoding=‘utf-8‘?>
<!--
  ~ Hibernate, Relational Persistence for Idiomatic Java
  ~
  ~ License: GNU Lesser General Public License (LGPL), version 2.1 or later.
  ~ See the lgpl.txt file in the root directory or <http://www.gnu.org/licenses/lgpl-2.1.html>.
  -->
<!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>

        <!-- Database connection settings -->
        <property name="connection.driver_class">oracle.jdbc.driver.OracleDriver</property>
        <property name="connection.url">jdbc:oracle:thin:@IP:PORT:orcl</property>
        <property name="connection.username">**</property>
        <property name="connection.password">**</property>

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

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

        <!-- Disable the second-level cache  -->
        <property name="cache.provider_class">org.hibernate.cache.internal.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="Event.hbm.xml"/>

    </session-factory>

</hibernate-configuration>

Application.java

package com.bf;

import java.util.List; 
import java.util.Date;
import java.util.Iterator; 
 
import org.hibernate.HibernateException; 
import org.hibernate.Session; 
import org.hibernate.Transaction;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;

@SuppressWarnings("unused")
public class Application {

  private static SessionFactory factory; 
    
  public static void main(String[] args) {
      try{
             factory = new Configuration().configure().buildSessionFactory();
      }catch (Throwable ex) { 
         System.err.println("Failed to create sessionFactory object." + ex);
         throw new ExceptionInInitializerError(ex); 
      }
      
    Session session = factory.openSession();
    session.beginTransaction();
    session.save( new Event( "Our very first event!", new Date() ) );
    session.save( new Event( "A follow up event", new Date() ) );
    session.getTransaction().commit();
    session.close();
  }
}

 3, 架构

SessionFactory 对象：根据hibernate.cfg.xml创建的式厂类，负责创建Session, 它是线程安全的。它是一个heavyweight 对象，在系统启动时负责创建，如果系统需要连接多个数据库，则相应的需要N个SessionFactory对象。

Session 对象：用来与数据库保持物理连接，它是一个轻量级对象，每次需要与数据库交互时就会创建该对象，数据持久化以及获取数据都需要它。它不宜保持open状态太长时间，因为它不是一直线程安全的，只在需要的时候才创建和销毁。

 

参考资料：http://www.tutorialspoint.com/hibernate/hibernate_architecture.htm