使用maven构建hibernate

1：建立maven project

2：pom中添加hibernate支持包

<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>5.1.31</version>
</dependency>

<dependency>
    <groupId>org.hibernate</groupId>
    <artifactId>hibernate-core</artifactId>
    <version>4.3.0.Final</version>
</dependency>

3：创建实体类User

public class User {
    private Long id;
    private String title;
    private Date date;
}

4：配置User.hbm.xml（文件放在工程根目录下）

<?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="com.zlt.hibernatedemo.User" table="user">
        <id name="id" column="id">
            <generator class="increment"></generator>
        </id>
        
        <property name="date" column="data" type="timestamp"></property>
        <property name="title"></property>
    </class>

</hibernate-mapping>

5：配置hibernate.cfg.xml（文件放在工程根目录下）

<?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>
        <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
        <property name="connection.url">jdbc:mysql://localhost:3306/hibernatetest</property>
        <property name="connection.username">root</property>
        <property name="connection.password">root</property>
        
        <property name="dialect">org.hibernate.dialect.MySQLDialect</property>
        <property name="show_sql">true</property>
        <property name="hbm2ddl.auto">create</property>
        
        <mapping resource="User.hbm.xml"/>
    </session-factory>

</hibernate-configuration>

6：创建session工具类 HibernateFactory.java

public class HibernateFactory {
    //sessionFactory是一个线程安全的全局对象，只需要创建一次
    public static final SessionFactory sessionFactory;
    
    static {
        try {
            sessionFactory = new Configuration().configure().buildSessionFactory();
        } catch (Throwable ex) {
            System.err.println("Initial SessionFactory creation failed." + ex);
            throw new ExceptionInInitializerError(ex);
        }
    }
    
    public static final ThreadLocal session = new ThreadLocal();

    public static Session currentSession() throws HibernateException {
        Session s = (Session) session.get();
        // Open a new Session, if this thread has none yet
        if (s == null) {
            s = sessionFactory.openSession();
            // Store it in the ThreadLocal variable
            session.set(s);
        }
        return s;
    }

    public static void closeSession() throws HibernateException {
        Session s = (Session) session.get();
        if (s != null)
            s.close();
        session.set(null);
    }
        
}

Configuration接口负责加载配置文件得到内部数据
Configuration config = new Configuration().configure("/hibernate.cfg.mxl"); //前面带"/"表示在src根目录下开始寻找
Configuration config = new Configuration().configure(); //自动搜寻hibernate.cfg.mxl

SessionFctory接口负责创建Session实例,Configuration实例config会根据配置信息构造SessionFactory实例并返回，因此config变更也不会影响到SessionFactory的实例，同样如果应用需要访问多个数据库，针对每个数据库，应分别对其创建相应的SessionFactory实例，SessionFactory保存了当前数据库配置的所有映射关系，同时也负责维护当前的二级数据缓存和Statement Pool，SessionFactory创建过程非常复杂而且线程安全，应用中针对一个数据库共享一个SessionFactory实例即可

SessionFactory sessionFactory = config.buildSessionFactory();

Session是hibernate持久化操作的基础类，提供了save，update，delete等方法
Session非线程安全，即一个Session实例同时只可由一个线程使用，一个Session实例的多线程并发调用会导致难以预知的错误
Session session = sessionFactory.openSession();

7：测试程序

public class HibernateTest {
    public static void main(String[] args) {
        Session session = HibernateFactory.currentSession();
        Transaction tx = session.beginTransaction();
        User user = new User();
        user.setDate(new Date());
        user.setTitle("title");
        session.save(user);
        
        tx.commit();
        session.close();
    }
}

8：结果