hibernate 基础知识

 1.hibernate的配置文件，一般放在classpath的根目录下，默认命名为hibernate.cfg.xml,代码例子如下：

<!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="hibernate.connection.driver_class">
        com.mysql.jdbc.Driver  
    </property>
    <property name="connection.url">jdbc:mysql:///test</property>
    <property name="connection.username">root</property>
    <property name="connection.password">admin</property>
    
    <property name="dialect">
        org.hibernate.dialect.MySQLDialect
    </property>
    <property name="hbm2ddl.auto">create-drop</property>
    <property name="show_sql">true</property>
    <mapping resource="cn/itcast/hibernate/domain/User.hbm.xml" />
</session-factory>
</hibernate-configuration>

 2.hibernate的映射文件，User.hbm.xml,代码例子如下:

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC 
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="cn.itcast.hibernate.domain">

    <class name="User">
        <id name="id">
            <generator class="native" />
        </id>
        <property name="name"/>
        <property name="birthday"/>
    </class>
</hibernate-mapping>

 3.数据操作类，代码例子：

package cn.itcast.hibernate;

import java.io.Serializable;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;

public final class HibernateUtil {
    private static SessionFactory sessionFactory;
    private static ThreadLocal session = new ThreadLocal();

    private HibernateUtil() {
    }

    static {
        Configuration cfg = new Configuration();
        cfg.configure();                          //如果配置文件路径或名字发生改变，那么就是cfg.configure("配置文件路径及名称");
        sessionFactory = cfg.buildSessionFactory();
    }

    public static Session getThreadLocalSession() {
        Session s = (Session) session.get();
        if (s == null) {
            s = getSession();
            session.set(s);
        }
        return s;
    }

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

    public static SessionFactory getSessionFactory() {
        return sessionFactory;
    }

    public static Session getSession() {
        return sessionFactory.openSession();
    }

    public static void add(Object entity) {
        Session s = null;
        Transaction tx = null;
        try {
            s = HibernateUtil.getSession();
            tx = s.beginTransaction();
            s.save(entity);
            tx.commit();
        } finally {
            if (s != null)
                s.close();
        }
    }

    public static void update(Object entity) {
        Session s = null;
        Transaction tx = null;
        try {
            s = HibernateUtil.getSession();
            tx = s.beginTransaction();
            s.update(entity);
            tx.commit();
        } finally {
            if (s != null)
                s.close();
        }
    }

    public static void delete(Object entity) {
        Session s = null;
        Transaction tx = null;
        try {
            s = HibernateUtil.getSession();
            tx = s.beginTransaction();
            s.delete(entity);
            tx.commit();
        } finally {
            if (s != null)
                s.close();
        }
    }

    public static Object get(Class clazz, Serializable id) {
        Session s = null;
        try {
            s = HibernateUtil.getSession();
            Object obj = s.get(clazz, id);
            return obj;
        } finally {
            if (s != null)
                s.close();
        }
    }
}