hibernate_03_session详解

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
     }
 }