1.1. 为什么要使用ORM？

面向对象的开发方法是当今企业级应用开发环境中的主流开发方法，关系数据库是企业级应用环境中永久存放数据的主流数据存储系统。

传统JDBC开发的问题：

开发烦琐，重复劳动。

非常了解操作数据库底层的API。

1. Hibernate简介

Hibernate是一个开源的ORM框架，它对JDBC进行了非常轻量级的对象封装，它将POJO与数据库表建立映射关系，是一个全自动的ORM框架。

注：Hibernate可以自动生成SQL语句、自动执行，使得Java程序员可以随心所欲的使用对象编程思维来操纵数据库（不建议自动生成）。

Hibernate可以应用在任何使用JDBC的场合，既可以在Java的客户端程序使用，也可以在Servlet/JSP的Web应用中使用，最具革命意义的是，Hibernate可以在应用EJB的J2EE架构中取代CMP，完成数据持久化的重任。

1.1. JDBC与Hibernate的比较

JDBC的速度最快，因为它是直连数据库。

而Hibernate是DAO层的框架，专门连接数据库，简化封装了JDBC，同时也牺牲一部分性能，所以Hibernate比JDBC慢很多。

l JDBC速度快，操作麻烦；

l Hibernate速度慢，操作简单；

l ibaites界于这两者之间。

如何添加相关的依赖

 1 <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 2   xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
 3   <modelVersion>4.0.0</modelVersion>
 4   <groupId>com.lww</groupId>
 5   <artifactId>T224_hibernate</artifactId>
 6   <packaging>war</packaging>
 7   <version>0.0.1-SNAPSHOT</version>
 8   <name>T224_hibernate Maven Webapp</name>
 9   <url>http://maven.apache.org</url>
10   <properties>
11         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
12         <maven.compiler.source>1.8</maven.compiler.source>
13         <maven.compiler.target>1.8</maven.compiler.target>
14         <junit.version>4.12</junit.version>
15         <servlet.version>4.0.0</servlet.version>
16         <hibernate.version>5.3.0.Final</hibernate.version>
17         <mysql.driver.version>5.1.46</mysql.driver.version>
18     </properties>
19  <dependencies>
20         <dependency>
21             <groupId>junit</groupId>
22             <artifactId>junit</artifactId>
23             <version>${junit.version}</version>
24             <scope>test</scope>
25         </dependency>
26 
27         <dependency>
28             <groupId>javax.servlet</groupId>
29             <artifactId>javax.servlet-api</artifactId>
30             <version>${servlet.version}</version>
31             <scope>provided</scope>
32         </dependency>
33 
34         <dependency>
35             <groupId>org.hibernate</groupId>
36             <artifactId>hibernate-core</artifactId>
37             <version>${hibernate.version}</version>
38         </dependency>
39 
40         <dependency>
41             <groupId>mysql</groupId>
42             <artifactId>mysql-connector-java</artifactId>
43             <version>${mysql.driver.version}</version>
44         </dependency>
45     </dependencies>
46   <build>
47     <finalName>T224_hibernate</finalName>
48    <plugins>
49             <plugin>
50                 <groupId>org.apache.maven.plugins</groupId>
51                 <artifactId>maven-compiler-plugin</artifactId>
52                 <version>3.7.0</version>
53                 <configuration>
54                     <source>${maven.compiler.source}</source>
55                     <target>${maven.compiler.target}</target>
56                     <encoding>${project.build.sourceEncoding}</encoding>
57                 </configuration>
58             </plugin>
59         </plugins>
60   </build>
61 </project>

2.在resource目录下添加hibernate.cfg.xml(核心配置文件)

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <!DOCTYPE hibernate-configuration PUBLIC
 3     "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
 4     "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
 5     
 6     <hibernate-configuration>
 7     <session-factory>
 8         <!-- 1. 数据库相关 -->
 9         <property name="connection.username">root</property>
10         <property name="connection.password">123</property>
11         <property name="connection.url">jdbc:mysql://localhost:3306/t224?useUnicode=true&amp;characterEncoding=UTF-8
12         </property>
13         <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
14         <property name="dialect">org.hibernate.dialect.MySQLDialect</property>
15 
16         <!-- 配置本地事务（No CurrentSessionContext configured!） -->
17         <property name="hibernate.current_session_context_class">thread</property>
18 
19         <!-- 2. 调试相关 -->
20         <property name="show_sql">true</property>
21         <property name="format_sql">true</property>
22 
23         <!-- 3. 添加实体映射文件 -->
24         <mapping resource="com/liuwenwu/one/entity/User.hbm.xml" />
25         
26     </session-factory>
27 </hibernate-configuration>

3.建立实体类User

 1 package com.liuwenwu.one.entity;
 2 import java.sql.Date;
 3 import java.sql.Timestamp;
 4 public class User {
 5     private Integer id;
 6     private String userName;
 7     private String userPwd;
 8     private String sex;
 9     private Date birthday;
10     private String realName;
11     private Timestamp createDatetime;
12     private String remark;
13     public Integer getId() {
14         return id;
15     }
16     public void setId(Integer id) {
17         this.id = id;
18     }
19     public String getUserName() {
20         return userName;
21     }
22     public void setUserName(String userName) {
23         this.userName = userName;
24     }
25     public String getUserPwd() {
26         return userPwd;
27     }
28     public void setUserPwd(String userPwd) {
29         this.userPwd = userPwd;
30     }
31     public String getSex() {
32         return sex;
33     }
34     public void setSex(String sex) {
35         this.sex = sex;
36     }
37     public Date getBirthday() {
38         return birthday;
39     }
40     public void setBirthday(Date birthday) {
41         this.birthday = birthday;
42     }
43     public String getRealName() {
44         return realName;
45     }
46     public void setRealName(String realName) {
47         this.realName = realName;
48     }
49     public Timestamp getCreateDatetime() {
50         return createDatetime;
51     }
52     public void setCreateDatetime(Timestamp createDatetime) {
53         this.createDatetime = createDatetime;
54     }
55     public String getRemark() {
56         return remark;
57     }
58     public void setRemark(String remark) {
59         this.remark = remark;
60     }
61     
62     public User() {
63         super();
64     }
65     public User(Integer id, String userName, String userPwd, String sex, Date birthday, String realName,
66             Timestamp createDatetime, String remark) {
67         super();
68         this.id = id;
69         this.userName = userName;
70         this.userPwd = userPwd;
71         this.sex = sex;
72         this.birthday = birthday;
73         this.realName = realName;
74         this.createDatetime = createDatetime;
75         this.remark = remark;
76     }
77     @Override
78     public String toString() {
79         return "User [id=" + id + ", userName=" + userName + ", userPwd=" + userPwd + ", sex=" + sex + ", birthday="
80                 + birthday + ", realName=" + realName + ", createDatetime=" + createDatetime + ", remark=" + remark
81                 + "]";
82     }
83 }

4.实体类的配置文件 User.hbm.xml 映射实体类（User）

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <!DOCTYPE hibernate-mapping PUBLIC 
 3     "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
 4     "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
 5 <hibernate-mapping>
 6     <!-- 
 7         class标签：
 8             name:对应的是需要映射的实体类的全路径名
 9             table:实体类对应的数据库中的表名
10         
11         id标签：    配置的是表中的主键
12             name:对应的是实体类属性名
13             type:指的是实体类数据类型
14             column：数据库表对应的列名
15             
16         property标签：配置除主键以为列段对应的类属性映射关系
17             name:对应的是实体类属性名
18             type:指的是实体类数据类型
19             column：数据库表对应的列名
20             insert="false" update="false" 表示该列段或者说该属性只做查询使用，不做更新(修改)
21              
22      -->
23     <class name="com.liuwenwu.one.entity.User" table="t_hibernate_user">
24         <id name="id" type="java.lang.Integer" column="id">
25             <generator class="increment" />
26         </id>
27         <property name="userName" type="java.lang.String" column="user_name">
28         </property>
29         <property name="userPwd" type="java.lang.String" column="user_pwd">
30         </property>
31         <property name="realName" type="java.lang.String" column="real_name">
32         </property>
33         <property name="sex" type="java.lang.String" column="sex">
34         </property>
35         <property name="birthday" type="java.sql.Date" column="birthday">
36         </property>
37         <property insert="false" update="false" name="createDatetime"
38             type="java.sql.Timestamp" column="create_datetime">
39         </property>
40         <property name="remark" type="java.lang.String" column="remark">
41         </property>
42     </class>
43 </hibernate-mapping>

接下来是CRUD的演示

查询：

 1 package com.liuwenwu.demo;
 2 import java.util.List;
 3 import org.hibernate.Session;
 4 import org.hibernate.SessionFactory;
 5 import org.hibernate.cfg.Configuration;
 6 
 7 /**
 8  * hibernate查询演示
 9  * @author ASUS
10  */
11 public class QueryDemo {
12     public static void main(String[] args) {
13         Configuration configure = new Configuration().configure("/hibernate.cfg.xml");
14         SessionFactory sessionFactory = configure.buildSessionFactory();
15         //会话 而这里的会话指的是操作数据库的链接
16         Session session = sessionFactory.openSession();
17         List list = session.createQuery("from User").list();
18         for (Object obj : list) {
19             System.out.println(obj);
20         }
21         session.close();
22     }
23 }

新增：

 1 package com.liuwenwu.demo;
 2 import java.sql.Date;
 3 import java.sql.Timestamp;
 4 import java.util.List;
 5 import org.hibernate.Session;
 6 import org.hibernate.SessionFactory;
 7 import org.hibernate.Transaction;
 8 import org.hibernate.cfg.Configuration;
 9 
10 import com.liuwenwu.one.entity.User;
11 
12 /**
13  * hibernate新增演示
14  * @author ASUS
15  *
16  */
17 public class InsertDemo {
18     public static void main(String[] args) {
19         Configuration configure = new Configuration().configure("/hibernate.cfg.xml");
20         SessionFactory sessionFactory = configure.buildSessionFactory();
21         //会话 而这里的会话指的是操作数据库的链接
22         Session session = sessionFactory.openSession();
23         Transaction transaction = session.beginTransaction();
24         session.save(new User(null, "aa", "版本", "男", new Date(System.currentTimeMillis()), "存储", new Timestamp(System.currentTimeMillis()), "信息"));
25         
26         transaction.commit();
27         session.close();
28     }
29     
30 }

修改：

 1 package com.liuwenwu.demo;
 2 
 3 import java.sql.Date;
 4 import java.sql.Timestamp;
 5 import org.hibernate.Session;
 6 import org.hibernate.SessionFactory;
 7 import org.hibernate.Transaction;
 8 import org.hibernate.cfg.Configuration;
 9 import com.liuwenwu.one.entity.User;
10 
11 /**
12  * hibernate修改演示
13  * @author ASUS
14  *
15  */
16 public class UpdateDemo {
17     public static void main(String[] args) {
18         Configuration configure = new Configuration().configure("/hibernate.cfg.xml");
19         SessionFactory sessionFactory = configure.buildSessionFactory();
20         //会话 而这里的会话指的是操作数据库的链接
21         Session session = sessionFactory.openSession();
22         Transaction transaction = session.beginTransaction();
23 //        session.save(new User(null, "aa", "版本", "男", new Date(System.currentTimeMillis()), "存储", new Timestamp(System.currentTimeMillis()), "信息"));
24 //        User u=new User(null, "aa", "版本", "男", new Date(System.currentTimeMillis()), "存储", new Timestamp(System.currentTimeMillis()), "信息");
25 //        u.setRealName("啥");
26         User user = session.get(User.class, 2);
27         user.setRealName("三毛");
28         transaction.commit();
29         session.close();
30     }
31 }

删除：

 1 package com.liuwenwu.demo;
 2 import org.hibernate.Session;
 3 import org.hibernate.SessionFactory;
 4 import org.hibernate.Transaction;
 5 import org.hibernate.cfg.Configuration;
 6 import com.liuwenwu.one.entity.User;
 7 
 8 /**
 9  * hibernate删除的演示
10  * @author ASUS
11  *
12  */
13 public class DeleteDemo {
14     public static void main(String[] args) {
15         Configuration configure = new Configuration().configure("/hibernate.cfg.xml");
16         SessionFactory sessionFactory = configure.buildSessionFactory();
17         //会话 而这里的会话指的是操作数据库的链接
18         Session session = sessionFactory.openSession();
19         Transaction transaction = session.beginTransaction();
20         User user = new User();
21         user.setId(2);
22         session.delete(user);
23         transaction.commit();
24         session.close();
25     }
26 }

Hibernate的管理对象的三种状态运行图解