在Java Web程序中使用Hibernate

在Java Web程序中使用Hibernate与普通Java程序一样。本文中将使用Servlet和JSP结合Hibernate实现数据库表的增删改查操作。

Web程序中，hibernate.cfg.xml中必须配置current_session_context_class参数。如果使用JBoss等内置Hibernae的容器，参数值要配置为jta，其他容器（如Tomcat等）需要配置为thread。

1. 创建工程并搭建Hibernate框架

在MyEclipse中创建一个Web工程，工程名为hibernate_web，把MySQL数据库驱动包和JSTL需要的jar包复制到WebRoot/WEB-INF/lib目录下；然后使用MyEclipse向导把Hibernate的jar包导到工程中。关于搭建Hibernate框架，可以参考网上的教程，这里就不再介绍了。接着，使用Hibernate连接数据库，并通过数据库表自动生成数据库对应的实体类和实体类映射文件。所使用的数据库表是MySQL的bank数据库中的users表。

自动生成及修改的代码如下：

package com.cn.vo;

/**
 * UsersVo entity. @author MyEclipse Persistence Tools
 */

public class UsersVo implements java.io.Serializable {

    // Fields

    private Integer id;
    private String name;
    private Integer age;
    private String tel;
    private String address;

    // Constructors

    /** default constructor */
    public UsersVo() {
    }

    /** minimal constructor */
    public UsersVo(Integer id) {
        this.id = id;
    }

    /** full constructor */
    public UsersVo(Integer id, String name, Integer age, String tel,
            String address) {
        this.id = id;
        this.name = name;
        this.age = age;
        this.tel = tel;
        this.address = address;
    }

    // Property accessors

    public Integer getId() {
        return this.id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return this.name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Integer getAge() {
        return this.age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    public String getTel() {
        return this.tel;
    }

    public void setTel(String tel) {
        this.tel = tel;
    }

    public String getAddress() {
        return this.address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

}

UsersVo.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">
<!-- 
    Mapping file autogenerated by MyEclipse Persistence Tools
-->
<hibernate-mapping>
    <class name="com.cn.vo.UsersVo" table="users" catalog="bank">
        <id name="id" type="java.lang.Integer">
            <column name="id" />
            <generator class="assigned" />
        </id>
        <property name="name" type="java.lang.String">
            <column name="name" length="20" />
        </property>
        <property name="age" type="java.lang.Integer">
            <column name="age" />
        </property>
        <property name="tel" type="java.lang.String">
            <column name="tel" length="20" />
        </property>
        <property name="address" type="java.lang.String">
            <column name="address" length="50" />
        </property>
    </class>
</hibernate-mapping>

hibernate.cfg.xml（修改）

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

<!-- Generated by MyEclipse Hibernate Tools.                   -->
<hibernate-configuration>

    <session-factory>    
        <!-- 声明使用SQL语句是MySQL数据库的SQL语句（MySQL方言） -->
        <property name="dialect">
            org.hibernate.dialect.MySQLDialect
        </property>
        
        <!-- 在控制台打印执行的SQL语句 -->
        <property name="show_sql">true</property>
        
        <!-- 指定Hibernate启动的时候自动更新表，如果不存在则创建 -->
        <property name="hbm2ddl.auto">update</property>
        
        <!-- 使用线程，防止遇到异常 -->
        <property name="current_session_context_class">thread</property>
        
            <!-- JDBC配置代码包括数据库驱动、用户名密码及连接地址 -->
        <property name="connection.url">
            jdbc:mysql://localhost:3306/bank
        </property>
        <property name="connection.username">root</property>
        <property name="connection.password">1234</property>
        <property name="connection.driver_class">
            com.mysql.jdbc.Driver
        </property>
        <property name="myeclipse.connection.profile">
            com.mysql.jdbc.Driver
        </property>
        
        <!-- 指定Hibernate的映射文件 -->
        <mapping resource="com/cn/vo/UsersVo.hbm.xml" />

    </session-factory>

</hibernate-configuration>

HibernateSessionFactory.java

package com.cn.hibernate;

import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.cfg.Configuration;

/**
 * Configures and provides access to Hibernate sessions, tied to the
 * current thread of execution.  Follows the Thread Local Session
 * pattern, see {@link http://hibernate.org/42.html }.
 */
public class HibernateSessionFactory {

    /** 
     * Location of hibernate.cfg.xml file.
     * Location should be on the classpath as Hibernate uses  
     * #resourceAsStream style lookup for its configuration file. 
     * The default classpath location of the hibernate config file is 
     * in the default package. Use #setConfigFile() to update 
     * the location of the configuration file for the current session.   
     */
    private static String CONFIG_FILE_LOCATION = "/hibernate.cfg.xml";
    private static final ThreadLocal<Session> threadLocal = new ThreadLocal<Session>();
    private  static Configuration configuration = new Configuration();    
    private static org.hibernate.SessionFactory sessionFactory;
    private static String configFile = CONFIG_FILE_LOCATION;

    static {
        try {
            configuration.configure(configFile);
            sessionFactory = configuration.buildSessionFactory();
        } catch (Exception e) {
            System.err
                    .println("%%%% Error Creating SessionFactory %%%%");
            e.printStackTrace();
        }
    }
    private HibernateSessionFactory() {
    }
    
    /**
     * Returns the ThreadLocal Session instance.  Lazy initialize
     * the <code>SessionFactory</code> if needed.
     *
     *  @return Session
     *  @throws HibernateException
     */
    public static Session getSession() throws HibernateException {
        Session session = (Session) threadLocal.get();

        if (session == null || !session.isOpen()) {
            if (sessionFactory == null) {
                rebuildSessionFactory();
            }
            session = (sessionFactory != null) ? sessionFactory.openSession()
                    : null;
            threadLocal.set(session);
        }

        return session;
    }

    /**
     *  Rebuild hibernate session factory
     *
     */
    public static void rebuildSessionFactory() {
        try {
            configuration.configure(configFile);
            sessionFactory = configuration.buildSessionFactory();
        } catch (Exception e) {
            System.err
                    .println("%%%% Error Creating SessionFactory %%%%");
            e.printStackTrace();
        }
    }

    /**
     *  Close the single hibernate session instance.
     *
     *  @throws HibernateException
     */
    public static void closeSession() throws HibernateException {
        Session session = (Session) threadLocal.get();
        threadLocal.set(null);

        if (session != null) {
            session.close();
        }
    }

    /**
     *  return session factory
     *
     */
    public static org.hibernate.SessionFactory getSessionFactory() {
        return sessionFactory;
    }

    /**
     *  return session factory
     *
     *    session factory will be rebuilded in the next call
     */
    public static void setConfigFile(String configFile) {
        HibernateSessionFactory.configFile = configFile;
        sessionFactory = null;
    }

    /**
     *  return hibernate configuration
     *
     */
    public static Configuration getConfiguration() {
        return configuration;
    }

}

2. 编写数据持久层

为了使程序结构清晰，数据持久层独立出来，放在DAO层中，在DAO层的类中编写数据的增删修改查方法，通过这些方法操作数据。在使用时，只需要根据实际情况来调用DAO层中的方法就可以了。这个例子中，DAO层只有一个类，类名为HibernateDao，HibernateDao类的代码如下：

package com.cn.dao;

import org.hibernate.HibernateException;
import org.hibernate.Session;

import java.util.List;

import com.cn.hibernate.HibernateSessionFactory;
import com.cn.vo.UsersVo;

public class HibernateDao {
    //添加数据的方法
    public void add(UsersVo usersVo){
        //调用HibernateSessionFactory的会话
        Session session = HibernateSessionFactory.getSession();
        try {
            session.beginTransaction(); //开启事务
            session.persist(usersVo); //将对象添加到数据库
            session.getTransaction().commit(); //提交事务
            
        } catch (Exception e) {
            session.getTransaction().rollback(); //回滚事务
        } finally {
            session.close(); //关闭session
        }
    }
    
    //修改数据的方法
    public void modifyUsers(UsersVo usersVo){
        Session session = HibernateSessionFactory.getSession();
        try {
            session.beginTransaction(); //开启事务
            session.update(usersVo); //修改数据
            session.getTransaction().commit(); //提交事务
        } catch (Exception e) {
            session.getTransaction().rollback(); //回滚事务
        } finally {
            session.close(); //关闭session
        }
    }
    
    //从表中删除数据
    public void delete(int id){
        Session session = HibernateSessionFactory.getSession();
        try {
            session.beginTransaction();
            UsersVo users = (UsersVo)session.get(UsersVo.class, id);
            session.delete(users);
            session.getTransaction().commit();
        } catch (Exception e) {
            session.getTransaction().rollback();
        } finally {
            session.close();
        }
    }
    
    //根据id查找数据
    @SuppressWarnings("unchecked")
    public UsersVo queryUsersById(int id){
        Session session = HibernateSessionFactory.getSession();
        UsersVo users = (UsersVo)session.get(UsersVo.class, id);
        return users;
    }
    
    //查找多条数据
    @SuppressWarnings("unchecked")
    public List<UsersVo> showlist(String hql){
        Session session = HibernateSessionFactory.getSession();
        try {
            session.beginTransaction();
            return session.createQuery(hql).list(); //使用HQL查询结果，返回List对象
        } catch (Exception e) {
            session.getTransaction().rollback();
        } finally {
            session.getTransaction().commit();
            session.close();
        }
        return null;
    }
}

该类中接受UsersVo类，Hibernate能够判断实体类的类型，决定操作哪个数据表。HibernateDao封装了最基本的CURD操作。