hibernate_03_session详解

Posted 2020-09-20

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：

 1 package com.imooc.hibernate;
 2 
 3 import java.util.Date;
 4 
 5 public class Students {
 6 
 7     private int sid;
 8     private String sname;
 9     private String gender;
10     private Date birthday;
11     private String address;
12 
13     public Students(int sid, String sname, String gender, Date birthday, String address) {
14         super();
15         this.sid = sid;
16         this.sname = sname;
17         this.gender = gender;
18         this.birthday = birthday;
19         this.address = address;
20     }
21 
22     @Override
23     public String toString() {
24         return "Students [sid=" + sid + ", sname=" + sname + ", gender=" + gender + ", birthday=" + birthday
25                 + ", address=" + address + "]";
26     }
27 
28     public int getSid() {
29         return sid;
30     }
31 
32     public void setSid(int sid) {
33         this.sid = sid;
34     }
35 
36     public String getSname() {
37         return sname;
38     }
39 
40     public void setSname(String sname) {
41         this.sname = sname;
42     }
43 
44     public String getGender() {
45         return gender;
46     }
47 
48     public void setGender(String gender) {
49         this.gender = gender;
50     }
51 
52     public Date getBirthday() {
53         return birthday;
54     }
55 
56     public void setBirthday(Date birthday) {
57         this.birthday = birthday;
58     }
59 
60     public String getAddress() {
61         return address;
62     }
63 
64     public void setAddress(String address) {
65         this.address = address;
66     }
67 }

java类的配置文件

 1 <?xml version="1.0"?>
 2 <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
 3 "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
 4 <!-- Generated 2017-5-23 0:24:09 by Hibernate Tools 3.5.0.Final -->
 5 <hibernate-mapping>
 6     <class name="com.imooc.hibernate.Students" table="STUDENTS">
 7         <id name="sid" type="int">
 8             <column name="SID" />
 9             <generator class="assigned" />
10         </id>
11         <property name="sname" type="java.lang.String">
12             <column name="SNAME" />
13         </property>
14         <property name="gender" type="java.lang.String">
15             <column name="GENDER" />
16         </property>
17         <property name="birthday" type="java.util.Date">
18             <column name="BIRTHDAY" />
19         </property>
20         <property name="address" type="java.lang.String">
21             <column name="ADDRESS" />
22         </property>
23     </class>
24 </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

 1 package com.icoom.test;
 2 
 3 import org.hibernate.Session;
 4 import org.hibernate.SessionFactory;
 5 import org.hibernate.cfg.Configuration;
 6 import org.hibernate.service.ServiceRegistry;
 7 import org.hibernate.service.ServiceRegistryBuilder;
 8 import org.junit.Test;
 9 
10 public class SessionTest {
11 
12     /*
13      * 使用openSession获得session对象
14      */
15     @Test
16     public void testOpenSession() {
17         Configuration config = new Configuration().configure();//获得配置对象（读取hibernate.cfg.xml文件）
18         // 获得服务注册对象
19         ServiceRegistry serviceRegistry = new ServiceRegistryBuilder().applySettings(config.getProperties()).buildServiceRegistry();
20         // 获得sessionFactory对象
21         SessionFactory sessionFactory = config.buildSessionFactory(serviceRegistry);
22         // 获得session对象
23         Session session = sessionFactory.openSession();
24         if (session != null) {
25             System.out.println("session创建成功");
26         } else {
27             System.out.println("session创建失败");
28         }
29     }
30     
31     /*
32      * 使用getCurrentSession获得session对象（需要在hibernate配置文件中设置）
33      */
34     @Test
35     public void testGetCurrentSession() {
36         Configuration config = new Configuration().configure();
37         ServiceRegistry serviceRegistry = new ServiceRegistryBuilder().applySettings(config.getProperties()).buildServiceRegistry();
38         SessionFactory sessionFactory = config.buildSessionFactory(serviceRegistry);
39         Session session = sessionFactory.getCurrentSession();
40         if (session != null) {
41             System.out.println("session创建成功！");
42         } else {
43             System.out.println("session创建失败！");
44         }
45     }
46 }

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。

 

 1 package com.icoom.test;
 2 
 3 import java.sql.Connection;
 4 import java.sql.SQLException;
 5 import java.util.Date;
 6 
 7 import org.hibernate.Session;
 8 import org.hibernate.SessionFactory;
 9 import org.hibernate.Transaction;
10 import org.hibernate.cfg.Configuration;
11 import org.hibernate.jdbc.Work;
12 import org.hibernate.service.ServiceRegistry;
13 import org.hibernate.service.ServiceRegistryBuilder;
14 import org.junit.Test;
15 
16 import com.imooc.hibernate.Students;
17 
18 public class SessionTest {
19 
20     @Test
21     public void saveStudentsByOpenSession() {
22 
23         // 获取配置对象
24         Configuration configure = new Configuration().configure();
25         // 获得服务注册对象
26         ServiceRegistry serviceRegistry = new ServiceRegistryBuilder().applySettings(configure.getProperties()).buildServiceRegistry();
27         /*
28          * 创建sessionFactory对象。sessionFactory是一种工厂模式，
29          * 目的是返回session，而不必new一个session。这样做比较安全。
30          */
31         SessionFactory sessionFactory = configure.buildSessionFactory(serviceRegistry);
32         // 创建第一个session对象
33         Session session1 = sessionFactory.openSession();
34         // 开启事务
35         Transaction transaction = session1.beginTransaction();
36         // 生成一个学生对象
37         Students s = new Students(1,"张三","男",new Date(),"北京");
38         session1.doWork(new Work() {
39 
40             @Override
41             public void execute(Connection connection) throws SQLException {
42                 // TODO Auto-generated method stub
43                 System.out.println("connection‘s hashCode:" + connection.hashCode());
44             }
45             
46         });
47         session1.save(s);
48 //        session1.close(); // 不执行close()方法,继续新建session对象
49         transaction.commit();
50         
51         // 创建第二个session对象
52         Session session2 = sessionFactory.openSession();
53         transaction = session2.beginTransaction();
54         s = new Students(2,"李四","女",new Date(),"上海");
55         session2.doWork(new Work() {
56 
57             @Override
58             public void execute(Connection connection) throws SQLException {
59                 // TODO Auto-generated method stub
60                 System.out.println("connection‘s hashCode:" + connection.hashCode());
61             }
62             
63         });
64         session2.save(s);
65         transaction.commit();
66     }
67 }

 

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()：

 1 package com.icoom.test;
 2 
 3 import java.sql.Connection;
 4 import java.sql.SQLException;
 5 import java.util.Date;
 6 
 7 import org.hibernate.Session;
 8 import org.hibernate.SessionFactory;
 9 import org.hibernate.Transaction;
10 import org.hibernate.cfg.Configuration;
11 import org.hibernate.jdbc.Work;
12 import org.hibernate.service.ServiceRegistry;
13 import org.hibernate.service.ServiceRegistryBuilder;
14 import org.junit.Test;
15 
16 import com.imooc.hibernate.Students;
17 
18 public class SessionTest {
19 
20     @Test
21     public void saveStudentsByGetCurrentSession() {
22 
23         // 获取配置对象
24         Configuration configure = new Configuration().configure();
25         // 获得服务注册对象
26         ServiceRegistry serviceRegistry = new ServiceRegistryBuilder().applySettings(configure.getProperties()).buildServiceRegistry();
27         /*
28          * 创建sessionFactory对象。sessionFactory是一种工厂模式，
29          * 目的是返回session，而不必new一个session。这样做比较安全。
30          */
31         SessionFactory sessionFactory = configure.buildSessionFactory(serviceRegistry);
32         // 创建第一个session对象
33         Session session1 = sessionFactory.getCurrentSession();
34         // 开启事务
35         Transaction transaction = session1.beginTransaction();
36         // 生成一个学生对象
37         Students s = new Students(1,"张三","男",new Date(),"北京");
38         session1.doWork(new Work() {
39 
40             @Override
41             public void execute(Connection connection) throws SQLException {
42                 // TODO Auto-generated method stub
43                 System.out.println("connection‘s hashCode:" + connection.hashCode());
44             }
45             
46         });
47         session1.save(s);
48 //        session1.close(); // 不执行close()方法,继续新建session对象
49         transaction.commit();
50         
51         // 创建第二个session对象
52         Session session2 = sessionFactory.getCurrentSession();
53         transaction = session2.beginTransaction();
54         s = new Students(2,"李四","女",new Date(),"上海");
55         session2.doWork(new Work() {
56 
57             @Override
58             public void execute(Connection connection) throws SQLException {
59                 // TODO Auto-generated method stub
60                 System.out.println("connection‘s hashCode:" + connection.hashCode());
61             }
62             
63         });
64         session2.save(s);
65 //        session2.close();
66         transaction.commit();
67     }
68 }

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。

 

 1 package com.icoom.test;
 2 
 3 import org.hibernate.Session;
 4 import org.hibernate.SessionFactory;
 5 import org.hibernate.cfg.Configuration;
 6 import org.hibernate.service.ServiceRegistry;
 7 import org.hibernate.service.ServiceRegistryBuilder;
 8 import org.junit.Test;
 9 
10 public class SessionTest {
11 
12     /*
13      * openSession每次创建新的session对象
14      */
15     @Test
16     public void testOpenSession() {
17         Configuration config = new Configuration().configure();//获得配置对象（读取hibernate.cfg.xml文件）
18         // 获得服务注册对象
19         ServiceRegistry serviceRegistry = new ServiceRegistryBuilder().applySettings(config.getProperties()).buildServiceRegistry();
20         // 获得sessionFactory对象
21         SessionFactory sessionFactory = config.buildSessionFactory(serviceRegistry);
22         // 获得session对象
23         Session session1 = sessionFactory.openSession();
24         Session session2 = sessionFactory.openSession();
25         System.out.println(session1 == session2); // false
26     }
27     
28     /*
29      * getCurrentSession使用现有的session对象
30      */
31     @Test
32     public void testGetCurrentSession() {
33         Configuration config = new Configuration().configure();
34         ServiceRegistry serviceRegistry = new ServiceRegistryBuilder().applySettings(config.getProperties()).buildServiceRegistry();
35         SessionFactory sessionFactory = config.buildSessionFactory(serviceRegistry);
36         Session session1 = sessionFactory.getCurrentSession();
37         Session session2 = sessionFactory.getCurrentSession();
38         System.out.println(session1 == session2); // true
39     }
40 }