Hibernate基础知识
 
概念： Hibernate是一个面向Java环境的对象/关系数据库映射的工具。Hibernate使用数据库和配置信息为应用程序提供持久化的服务。
作用：Hibernate对JDBC进行了对象封装，使得Java程序员可以随心所欲地使用对象编程思维来操纵数据库，Hibernate不仅仅管理Java类到数据库表的映射，还可以提供数据查询和获取数据的方法，可以大幅减少开发时人工使用SQL和JDBC处理数据的时间。
原理：用公共类实现数据库的连接，查询，删除，更新以及关闭连接等操作。把连接信息配置在文本文件中，这样修改环境不需要编译Java文件。对操作结束后的连接不马上关闭，而是维持一个合理的空间连接数，获取连接也不一定完全新建连接，可以从空闲连接池中获取。数据库操作不局限于表、列的形式，而可以把表映射为类对象，对数据库连接池、会话的管理实行统一的框架化。
 
实践：
一、新建项目并配置环境：
1、新建一个项目目录d:\myprojects\hibernatetest,在项目目录下新建两个子目录src、lib，其中src目录用于存放源文件和xml文件，lib目录用于存放项目开发需要的库文件和数据库驱动程序。
2、创建名为testdb的mysql数据库，并建立数据表students
二、编写持久化类
package entity;

/**
* Created by IntelliJ IDEA.
* User: xiaohui
* Date: 2008-12-4 11:34:01
*/
public class Student {
        private long id;
        private String name;
        private int age;
        private String degree;
        private String speciality;

        public Student() {
        }

        public Student(String name, int age, String degree, String speciality) {
                this.name = name;
                this.age = age;
                this.degree = degree;
                this.speciality = speciality;
        }

        public long getId() {
                return id;
        }

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

        public String getName() {
                return name;
        }

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

        public int getAge() {
                return age;
        }

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

        public String getDegree() {
                return degree;
        }

        public void setDegree(String degree) {
                this.degree = degree;
        }

        public String getSpeciality() {
                return speciality;
        }

        public void setSpeciality(String speciality) {
                this.speciality = speciality;
        }

        @Override
        public String toString() {
                return "Student{" +
                                "id=" + id +
                                ", name='" + name + '\'' +
                                ", age=" + age +
                                ", degree='" + degree + '\'' +
                                ", speciality='" + speciality + '\'' +
                                '}';
        }
}

三、编写映射文件
<?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="entity.Student" table="Student">
                <id name="id" type="java.lang.Long">
                        <column name="id"/>
                        <generator class="native"></generator>
                </id>
                <property name="name" type="java.lang.String" column="name"/>
                <property name="age" type="java.lang.Integer" column="age"/>
                <property name="degree" type="java.lang.String" column="degree"/>
                <property name="speciality" type="java.lang.String" column="speciality"/>
        </class>
</hibernate-mapping>

四、Hibernate配置
<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
                "-//Hibernate/Hibernate Configuration DTD//EN"
                "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
        <session-factory>
                <property name="connection.url">jdbc:mysql://localhost:3306/testdb</property>
                <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
                <property name="connection.username">root</property>
                <property name="connection.password">xiaohui</property>
                <!-- DB schema will be updated if needed -->
                <property name="hbm2ddl.auto">update</property>
                <property name="show_sql">true</property>
                <property name="format_sql">true</property>
                <property name="connection.autocommit">true</property>

                <mapping resource="entity/User.hbm.xml"/>
                <mapping resource="entity/News.hbm.xml"/>
                <mapping resource="entity/Student.hbm.xml"/>
        </session-factory>
</hibernate-configuration>

五、编写应用文件
package dao;

import utils.BaseDAO;
import entity.Student;
import org.hibernate.Session;


/**
* Created by IntelliJ IDEA.
* User: xiaohui
* Date: 2008-12-4 12:18:13
*/
public class StudentDAO extends BaseDAO {
        public Student saveStudnet(Student student){
                Session session=getSession();
                session.save(student);
                session.close();
                return student;

        }

        public static void main(String[] args) {
            Student student=new Student();
            student.setName("小周");
            student.setAge(22);
            student.setDegree("本科");
            student.setSpeciality("装潢设计");
            StudentDAO studentDAO=new StudentDAO();
            studentDAO.saveStudnet(student);

                System.out.println(student);
        }

}
运行结果：

log4j:WARN No appenders could be found for logger (org.hibernate.cfg.Environment).
log4j:WARN Please initialize the log4j system properly.
Hibernate:    
        insert    
        into
                Student
                (name, age, degree, speciality)    
        values
                (?, ?, ?, ?)
Student{id=14, name='小周', age=22, degree='本科', speciality='装潢设计'}

Process finished with exit code 0