23hibernate_pessimistic_locking

悲观锁

悲观锁的实现，通常依赖于数据库机制，在整个过程中将数据锁定，其它任何用户都不能读取或修改
ExportDB:
create table t_inventory (itemNo integer not null auto_increment, itemName varchar(255), quantity integer, primary key (itemNo))


public class Inventory {

    private int itemNo;
    
    private String itemName;
    
    private int quantity;
    
    <hibernate-mapping>
    <class name="com.bjsxt.hibernate.Inventory" table="t_inventory">
        <id name="itemNo">
            <generator class="native"/>
        </id>
        <property name="itemName"/>
        <property name="quantity"/>
    </class>
</hibernate-mapping>

package com.bjsxt.hibernate;

import org.hibernate.Session;

public class InitData {

    public static void main(String[] args) {
        Session session = null;
        try {
            session = HibernateUtils.getSession();
            session.beginTransaction();
            
            Inventory inv = new  Inventory();
            inv.setItemNo(1001);
            inv.setItemName("脑白金");
            inv.setQuantity(1000);
            
            session.save(inv);
            session.getTransaction().commit();
        }catch(Exception e) {
            e.printStackTrace();
            session.getTransaction().rollback();
        }finally {
            HibernateUtils.closeSession(session);
        }    
    }
}

Hibernate: insert into t_inventory (itemName, quantity) values (?, ?)

mysql> select *   from t_inventory;
+--------+----------+----------+
| itemNo | itemName | quantity |
+--------+----------+----------+
|      1 | 脑白金   |     1000 |
+--------+----------+----------+
1 row in set (0.00 sec)

TestLoad1:
public void testLoad1() {
        Session session = null;
        try {
            session = HibernateUtils.getSession();
            session.beginTransaction();
            
            Inventory inv = (Inventory)session.load(Inventory.class, 1, LockMode.UPGRADE);
            System.out.println("itemName=" + inv.getItemName());
            System.out.println("quantity=" + inv.getQuantity());
            inv.setQuantity(inv.getQuantity() - 200);//1000
            session.update(inv);
            session.getTransaction().commit();
        }catch(Exception e) {
            e.printStackTrace();
            session.getTransaction().rollback();
        }finally {
            HibernateUtils.closeSession(session);
        }    
    }
Hibernate: select inventory0_.itemNo as itemNo0_0_, inventory0_.itemName as itemName0_0_, inventory0_.quantity as quantity0_0_ from t_inventory inventory0_ where inventory0_.itemNo=? for update

TestLoad2:

public void testLoad2() {
        Session session = null;
        try {
            session = HibernateUtils.getSession();
            session.beginTransaction();
            
            Inventory inv = (Inventory)session.load(Inventory.class, 1, LockMode.UPGRADE);
            System.out.println("itemName=" + inv.getItemName());
            System.out.println("quantity=" + inv.getQuantity());
            inv.setQuantity(inv.getQuantity() - 200);
            session.update(inv);
            session.getTransaction().commit();
        }catch(Exception e) {
            e.printStackTrace();
            session.getTransaction().rollback();
        }finally {
            HibernateUtils.closeSession(session);
        }    
    }
mysql> select *   from t_inventory;
+--------+----------+----------+
| itemNo | itemName | quantity |
+--------+----------+----------+
|      1 | 脑白金   |     1000 |
+--------+----------+----------+
1 row in set (0.00 sec)

TestLoad1:
Hibernate: select inventory0_.itemNo as itemNo0_0_, inventory0_.itemName as itemName0_0_, inventory0_.quantity as quantity0_0_ from t_inventory inventory0_ where inventory0_.itemNo=? for update

TestLoad2:等待第一个事务的提交
Hibernate: select inventory0_.itemNo as itemNo0_0_, inventory0_.itemName as itemName0_0_, inventory0_.quantity as quantity0_0_ from t_inventory inventory0_ where inventory0_.itemNo=? for update


quantity=600
Hibernate: update t_inventory set itemName=?, quantity=? where itemNo=?
Hibernate: select inventory0_.itemNo as itemNo0_0_, inventory0_.itemName as itemName0_0_, inventory0_.quantity as quantity0_0_ from t_inventory inventory0_ where inventory0_.itemNo=? for update


mysql> select *   from t_inventory;
+--------+----------+----------+
| itemNo | itemName | quantity |
+--------+----------+----------+
|      1 | 脑白金   |      600 |
+--------+----------+----------+
1 row in set (0.00 sec)