Hibernate实现悲观锁和乐观锁代码介绍

package com.bjsxt.hibernate; 
import javax.persistence.Entity; 
import javax.persistence.GeneratedValue; 
import javax.persistence.Id; 
@Entity 
public class Account { 
private int id; 
private int balance; //BigDecimal 
@Id 
@GeneratedValue 
public int getId() { 
return id; 
} 
public void setId(int id) { 
this.id = id; 
} 
public int getBalance() { 
return balance; 
} 
public void setBalance(int balance) { 
this.balance = balance; 
} 
} 

<mapping class="com.bjsxt.hibernate.Account"/> 

@Test 
public void testSave() { 
Session session = sf.openSession(); 
session.beginTransaction(); 
Account a = new Account(); 
a.setBalance(100); 
session.save(a); 
session.getTransaction().commit(); 
session.close(); 
} 
@Test 
public void testOperation1() { 
Session session = sf.openSession(); 
session.beginTransaction(); 
Account a = (Account)session.load(Account.class, 1); 
int balance = a.getBalance(); 
//do some caculations 
balance = balance - 10; 
//在保存时很有可能会把在同一时期修改的给覆盖掉 
//这个时候上一把"锁"就可以避免这个问题 
a.setBalance(balance); 
session.getTransaction().commit(); 
session.close(); 
} 
//下面这个就是对上面那个例子做的修改 
@Test 
public void testPessimisticLock() { 
Session session = sf.openSession(); 
session.beginTransaction(); 
//给它加把锁，加锁的机制上面已经提到了 
Account a = (Account)session.load(Account.class, 1, LockMode.UPGRADE); 
int balance = a.getBalance(); 
//do some caculation 
balance = balance - 10; 
a.setBalance(balance); 
session.getTransaction().commit(); 
session.close(); 
} 

package com.bjsxt.hibernate;  
import javax.persistence.Entity; 
import javax.persistence.GeneratedValue; 
import javax.persistence.Id; 
import javax.persistence.Version;  
@Entity 
public class Account { 
private int id; 
private int balance; 
private int version;  
@Version//加了这个注解就说明这个是专门用来做版本标注的 
public int getVersion() { 
return version; 
} 
public void setVersion(int version) { 
this.version = version; 
} 
@Id 
@GeneratedValue 
public int getId() { 
return id; 
} 
public void setId(int id) { 
this.id = id; 
} 
public int getBalance() { 
return balance; 
} 
public void setBalance(int balance) { 
this.balance = balance; 
} 
} 

 @Test 
public void testSave() { 
Session session = sf.openSession(); 
session.beginTransaction(); 
Account a = new Account(); 
a.setBalance(100); 
session.save(a); 
session.getTransaction().commit(); 
session.close(); 
} 
@Test 
public void testOptimisticLock() { 
Session session = sf.openSession(); 
Session session2 = sf.openSession(); 
session.beginTransaction(); 
Account a1 = (Account) session.load(Account.class, 1); 
session2.beginTransaction(); 
Account a2 = (Account) session2.load(Account.class, 1); 
a1.setBalance(900); 
a2.setBalance(1100); 
//第一个session一旦提交，version就会+1 
session.getTransaction().commit(); 
System.out.println(a1.getVersion()); 
//第二个session提交的时候，一看version不一样就会报错 
//出了错误做个记录，下次再提交(也可以用其他方法) 
        session2.getTransaction().commit(); 
System.out.println(a2.getVersion()); 
session.close(); 
session2.close(); 
}