为什么取1248
二进制
CRUD
移位效率高
在并发和效率选择一个平衡点
一般不会考虑幻读 因为我们不会再一个事务里查询两次，（只能设置为seralizable）
悲观锁和乐观锁的前提是read-uncommitted
在数据库中 默认是repeatable read
悲观锁是想着总有人要更改 所以使用数据库的锁
乐观锁是在程序级别的 设置一个版本号 如果前后不一致就进行自己的操作
例子
悲观所
Acocount
package com.bjsxt.hibernate;import javax.persistence.Entity;import javax.persistence.GeneratedValue;import javax.persistence.Id;@Entitypublic 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; ???} ???????}Test
???@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; ???????a.setBalance(balance); ???????session.getTransaction().commit(); ???????session.close(); ???} ???????@Test ???public void testPessimisticLock() { ???????Session session = sf.openSession(); ???????session.beginTransaction(); ???????????????Account a = (Account)session.load(Account.class, 1, LockMode.UPGRADE); ??//设置数据库锁 不让其他事务访问 ???????int balance = a.getBalance(); ???????//do some caculation ???????balance = balance - 10; ???????a.setBalance(balance); ???????session.getTransaction().commit(); ???????session.close(); ???} ???乐观锁
Account
package com.bjsxt.hibernate;import javax.persistence.Entity;import javax.persistence.GeneratedValue;import javax.persistence.Id;import javax.persistence.Version; ?????????//注意：Version 不用自己设置@Entitypublic class Account { ???private int id; ???private int balance; ???private int version; ???@Version ???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 testSchemaExport() { ???????new SchemaExport(new AnnotationConfiguration().configure()).create( ???????????????false, true); ???} ???@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); ??//Version不用自己设置 ???????????????a1.setBalance(900); ???????a2.setBalance(1100); ???????session.getTransaction().commit(); ???????System.out.println(a1.getVersion()); ???????session2.getTransaction().commit(); ???????System.out.println(a2.getVersion()); ???????session.close(); ???????session2.close(); ???}Hibernate 再接触 ?悲观锁和乐观锁
原文地址：https://www.cnblogs.com/frankzone/p/9607307.html