获得session对象有两种方法：

1)openSession

2)getCurrentSession

　　如果使用的是getCurrentSession需要在hibernate.cfg.xml文件中进行配置：

　　如果是本地事务(jdbc事务)，按照如下方法配置：

　　  <property name="hibernate.current_session_context_class">thread</property>

　　如果是全局事务(jta事务)

　　  <property name="hibernate.current_session_context_class">jta</property>

例子：

先创建java类：

 package com.imooc.hibernate;

 import java.util.Date;

 public class Students {

     private int sid;

     private String sname;

     private String gender;

     private Date birthday;

     private String address;

     public Students(int sid, String sname, String gender, Date birthday, String address) {

         super();

         this.sid = sid;

         this.sname = sname;

         this.gender = gender;

         this.birthday = birthday;

         this.address = address;

     }

     @Override

     public String toString() {

         return "Students [sid=" + sid + ", sname=" + sname + ", gender=" + gender + ", birthday=" + birthday

                 + ", address=" + address + "]";

     }

     public int getSid() {

         return sid;

     }

     public void setSid(int sid) {

         this.sid = sid;

     }

     public String getSname() {

         return sname;

     }

     public void setSname(String sname) {

         this.sname = sname;

     }

     public String getGender() {

         return gender;

     }

     public void setGender(String gender) {

         this.gender = gender;

     }

     public Date getBirthday() {

         return birthday;

     }

     public void setBirthday(Date birthday) {

         this.birthday = birthday;

     }

     public String getAddress() {

         return address;

     }

     public void setAddress(String address) {

         this.address = address;

     }

 }

java类的配置文件

 <?xml version="1.0"?>

 <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"

 "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

 <!-- Generated 2017-5-23 0:24:09 by Hibernate Tools 3.5.0.Final -->

 <hibernate-mapping>

     <class name="com.imooc.hibernate.Students" table="STUDENTS">

         <id name="sid" type="int">

             <column name="SID" />

             <generator class="assigned" />

         </id>

         <property name="sname" type="java.lang.String">

             <column name="SNAME" />

         </property>

         <property name="gender" type="java.lang.String">

             <column name="GENDER" />

         </property>

         <property name="birthday" type="java.util.Date">

             <column name="BIRTHDAY" />

         </property>

         <property name="address" type="java.lang.String">

             <column name="ADDRESS" />

         </property>

     </class>

 </hibernate-mapping>

hibernate配置文件

<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE hibernate-configuration PUBLIC

        "-//Hibernate/Hibernate Configuration DTD 3.0//EN"

        "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">

<hibernate-configuration>

    <session-factory>

        <property name="connection.username">root</property>

        <property name="connection.password">root</property>

        <property name="connection.driver_class">com.mysql.jdbc.Driver</property>

        <property name="connection.url">jdbc:mysql://localhost:3306/hibernate?useUnicode=true&amp;characterEncoding=UTF-8</property>

        <property name="dialect">org.hibernate.dialect.MySQLDialect</property>

        <!-- 是否将sql语句打印到控制台，编码阶段便于测试，建议设为true -->

        <property name="show_sql">true</property>

        <!-- 是否将sql语句进行排版，建议设为true -->

        <property name="format_sql">true</property>

        <!-- 生成表结构的策略。create是如果之前有表结构，先删除表结构再重建；

            update：原有的基础上更新；

            create-drop：先删除表结构再重建

            validate：与原表进行验证，如果和原表表结构不同，则不进行创建。

            一般使用create和update

         -->

        <property name="hbm2ddl.auto">create</property>

        <!-- 使用getCurrentSession方法必须在配置文件中配置 -->

        <property name="hibernate.current_session_context_class">thread</property>

        <mapping resource="com/imooc/hibernate/Students.hbm.xml"/>

    </session-factory>

</hibernate-configuration>

测试类

 package com.icoom.test;

 import org.hibernate.Session;

 import org.hibernate.SessionFactory;

 import org.hibernate.cfg.Configuration;

 import org.hibernate.service.ServiceRegistry;

 import org.hibernate.service.ServiceRegistryBuilder;

 import org.junit.Test;

 public class SessionTest {

     /*

      * 使用openSession获得session对象

      */

     @Test

     public void testOpenSession() {

         Configuration config = new Configuration().configure();//获得配置对象（读取hibernate.cfg.xml文件）

         // 获得服务注册对象

         ServiceRegistry serviceRegistry = new ServiceRegistryBuilder().applySettings(config.getProperties()).buildServiceRegistry();

         // 获得sessionFactory对象

         SessionFactory sessionFactory = config.buildSessionFactory(serviceRegistry);

         // 获得session对象

         Session session = sessionFactory.openSession();

         if (session != null) {

             System.out.println("session创建成功");

         } else {

             System.out.println("session创建失败");

         }

     }

     /*

      * 使用getCurrentSession获得session对象（需要在hibernate配置文件中设置）

      */

     @Test

     public void testGetCurrentSession() {

         Configuration config = new Configuration().configure();

         ServiceRegistry serviceRegistry = new ServiceRegistryBuilder().applySettings(config.getProperties()).buildServiceRegistry();

         SessionFactory sessionFactory = config.buildSessionFactory(serviceRegistry);

         Session session = sessionFactory.getCurrentSession();

         if (session != null) {

             System.out.println("session创建成功！");

         } else {

             System.out.println("session创建失败！");

         }

     }

 }

那么，openSession和getCurrentSession有什么区别？

1. getCurrentSession在事务提交或者回滚之后会自动关闭，openSession需要手动关闭。如果使用openSession而没有手动关闭，多次之后会导致连接池溢出。

 package com.icoom.test;

 import java.sql.Connection;

 import java.sql.SQLException;

 import java.util.Date;

 import org.hibernate.Session;

 import org.hibernate.SessionFactory;

 import org.hibernate.Transaction;

 import org.hibernate.cfg.Configuration;

 import org.hibernate.jdbc.Work;

 import org.hibernate.service.ServiceRegistry;

 import org.hibernate.service.ServiceRegistryBuilder;

 import org.junit.Test;

 import com.imooc.hibernate.Students;

 public class SessionTest {

     @Test

     public void saveStudentsByOpenSession() {

         // 获取配置对象

         Configuration configure = new Configuration().configure();

         // 获得服务注册对象

         ServiceRegistry serviceRegistry = new ServiceRegistryBuilder().applySettings(configure.getProperties()).buildServiceRegistry();

         /*

          * 创建sessionFactory对象。sessionFactory是一种工厂模式，

          * 目的是返回session，而不必new一个session。这样做比较安全。

          */

         SessionFactory sessionFactory = configure.buildSessionFactory(serviceRegistry);

         // 创建第一个session对象

         Session session1 = sessionFactory.openSession();

         // 开启事务

         Transaction transaction = session1.beginTransaction();

         // 生成一个学生对象

         Students s = new Students(1,"张三","男",new Date(),"北京");

         session1.doWork(new Work() {

             @Override

             public void execute(Connection connection) throws SQLException {

                 // TODO Auto-generated method stub

                 System.out.println("connection's hashCode:" + connection.hashCode());

             }

         });

         session1.save(s);

 //        session1.close(); // 不执行close()方法,继续新建session对象

         transaction.commit();

         // 创建第二个session对象

         Session session2 = sessionFactory.openSession();

         transaction = session2.beginTransaction();

         s = new Students(2,"李四","女",new Date(),"上海");

         session2.doWork(new Work() {

             @Override

             public void execute(Connection connection) throws SQLException {

                 // TODO Auto-generated method stub

                 System.out.println("connection's hashCode:" + connection.hashCode());

             }

         });

         session2.save(s);

         transaction.commit();

     }

 }

控制台打印出两个hashcode值不同，所以使用openSession()方法而不手动关闭，每次创建都会新建一个链接，有可能导致连接池溢出。

再看getCurrentSession()：

 package com.icoom.test;

 import java.sql.Connection;

 import java.sql.SQLException;

 import java.util.Date;

 import org.hibernate.Session;

 import org.hibernate.SessionFactory;

 import org.hibernate.Transaction;

 import org.hibernate.cfg.Configuration;

 import org.hibernate.jdbc.Work;

 import org.hibernate.service.ServiceRegistry;

 import org.hibernate.service.ServiceRegistryBuilder;

 import org.junit.Test;

 import com.imooc.hibernate.Students;

 public class SessionTest {

     @Test

     public void saveStudentsByGetCurrentSession() {

         // 获取配置对象

         Configuration configure = new Configuration().configure();

         // 获得服务注册对象

         ServiceRegistry serviceRegistry = new ServiceRegistryBuilder().applySettings(configure.getProperties()).buildServiceRegistry();

         /*

          * 创建sessionFactory对象。sessionFactory是一种工厂模式，

          * 目的是返回session，而不必new一个session。这样做比较安全。

          */

         SessionFactory sessionFactory = configure.buildSessionFactory(serviceRegistry);

         // 创建第一个session对象

         Session session1 = sessionFactory.getCurrentSession();

         // 开启事务

         Transaction transaction = session1.beginTransaction();

         // 生成一个学生对象

         Students s = new Students(1,"张三","男",new Date(),"北京");

         session1.doWork(new Work() {

             @Override

             public void execute(Connection connection) throws SQLException {

                 // TODO Auto-generated method stub

                 System.out.println("connection's hashCode:" + connection.hashCode());

             }

         });

         session1.save(s);

 //        session1.close(); // 不执行close()方法,继续新建session对象

         transaction.commit();

         // 创建第二个session对象

         Session session2 = sessionFactory.getCurrentSession();

         transaction = session2.beginTransaction();

         s = new Students(2,"李四","女",new Date(),"上海");

         session2.doWork(new Work() {

             @Override

             public void execute(Connection connection) throws SQLException {

                 // TODO Auto-generated method stub

                 System.out.println("connection's hashCode:" + connection.hashCode());

             }

         });

         session2.save(s);

 //        session2.close();

         transaction.commit();

     }

 }

两个hashCode一致。

2. openSession每次创建新的session对象，getCurrentSession使用现有的session对象。

 package com.icoom.test;

 import org.hibernate.Session;

 import org.hibernate.SessionFactory;

 import org.hibernate.cfg.Configuration;

 import org.hibernate.service.ServiceRegistry;

 import org.hibernate.service.ServiceRegistryBuilder;

 import org.junit.Test;

 public class SessionTest {

     /*

      * openSession每次创建新的session对象

      */

     @Test

     public void testOpenSession() {

         Configuration config = new Configuration().configure();//获得配置对象（读取hibernate.cfg.xml文件）

         // 获得服务注册对象

         ServiceRegistry serviceRegistry = new ServiceRegistryBuilder().applySettings(config.getProperties()).buildServiceRegistry();

         // 获得sessionFactory对象

         SessionFactory sessionFactory = config.buildSessionFactory(serviceRegistry);

         // 获得session对象

         Session session1 = sessionFactory.openSession();

         Session session2 = sessionFactory.openSession();

         System.out.println(session1 == session2); // false

     }

     /*

      * getCurrentSession使用现有的session对象

      */

     @Test

     public void testGetCurrentSession() {

         Configuration config = new Configuration().configure();

         ServiceRegistry serviceRegistry = new ServiceRegistryBuilder().applySettings(config.getProperties()).buildServiceRegistry();

         SessionFactory sessionFactory = config.buildSessionFactory(serviceRegistry);

         Session session1 = sessionFactory.getCurrentSession();

         Session session2 = sessionFactory.getCurrentSession();

         System.out.println(session1 == session2); // true

     }

 }

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