并发实际场景（保持余额操作的正确：数据库余额字段版）
场景：
一个人在一家银行办了一个账户，银行给了 一张卡（存取款）、一本存折（存取款）、一个网银（查询余额）
卡和存储不断存款和取款，网银不断查询余额。如何保持余额的正确。
数据库余额表：原本想用版本号来实现的，后面弃用version字段。
DROP TABLE IF EXISTS `t_test`;
CREATE TABLE `t_test` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`account` decimal(11,2) DEFAULT NULL,
`version` int(100) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8;
-- ----------------------------
-- Records of t_test
-- ----------------------------
INSERT INTO `t_test` VALUES ('1', '50.00', '1');
mapper.xml文件：仔细看两个sql的写法，这里是重点，请不要在java代码中进行余额的加减操作。
update t_test
set account = account + #{newAccount,jdbcType=DECIMAL}
where id = #{id,jdbcType=INTEGER}
update t_test
set account = account - #{newAccount,jdbcType=DECIMAL}
where id = #{id,jdbcType=INTEGER} and account >= #{newAccount,jdbcType=DECIMAL}
dao暂时不贴出：
service：请在每个方法上加入事物和synchronized。
@Service
public class TestServiceImpl implements TestService {
@Autowired
private TTestMapper testMapper;
/**
* 存钱
*
* @param money
*/
@Override
@Transactional
public synchronized BigDecimal addAcount(String name, int money) throws TransactionalException {
TTest tTest = testMapper.selectByPrimaryKey(1);
tTest.setNewAccount(new BigDecimal(money));
int i = testMapper.updateAccountAdd(tTest);
if (i == 0){
System.out.println("添加余额失败！余额=" + tTest.getAccount());
return new BigDecimal(money);
}
System.out.println(name + "...存入：" + money + "..." + Thread.currentThread().getName());
return selectAcount(name);
}
/**
* 取钱
*
* @param money
*/
@Override
@Transactional
public synchronized BigDecimal subAcount(String name, int money) throws TransactionalException{
TTest tTest = testMapper.selectByPrimaryKey(1);
tTest.setNewAccount(new BigDecimal(money));
int i = testMapper.updateAccountSub(tTest);
if (i == 0){
System.out.println("账户余额不足！余额=" + tTest.getAccount());
return new BigDecimal(money);
}
System.out.println(name + "...取出：" + money + "..." + Thread.currentThread().getName());
return selectAcount(name);
}
/**
* 查询余额
*/
@Override
@Transactional
public synchronized BigDecimal selectAcount(String name) throws TransactionalException{
TTest tTest = testMapper.selectByPrimaryKey(1);
System.out.println(name + "...余额：" + tTest.getAccount());
return tTest.getAccount();
}
}
controller:
@Controller
public class TestMysqlController {
@Autowired
private TestService testService;
@RequestMapping(value="/cardAddAcountMysql")
@ResponseBody
public TaotaoResult cardAddAcount() throws TransactionalException{
TaotaoResult result = new TaotaoResult();
result.setData("+100, 余额： " + testService.addAcount("card", 100));
return result;
}
@RequestMapping(value="/passbookAddAcountMysql")
@ResponseBody
public TaotaoResult passbookAddAcount() throws TransactionalException{
TaotaoResult result = new TaotaoResult();
result.setData("+100, 余额： " + testService.addAcount("存折", 100));
return result;
}
@RequestMapping(value="/cardSubAcountMysql")
@ResponseBody
public TaotaoResult cardSubAcount(){
TaotaoResult result = new TaotaoResult();
result.setData("-150, 余额： " + testService.subAcount("card", 150));
return result;
}
@RequestMapping(value="/passbookSubAcountMysql")
@ResponseBody
public TaotaoResult passbookSubAcount() throws TransactionalException{
TaotaoResult result = new TaotaoResult();
result.setData("-200, 余额： " + testService.subAcount("存折", 200));
return result;
}
@RequestMapping(value="/selectAcountMysql")
@ResponseBody
public TaotaoResult selectAcount() throws TransactionalException {
TaotaoResult result = new TaotaoResult();
result.setData(testService.selectAcount(""));
return result;
}
}
执行结果：
card...余额：2850.00
card...取出：150...http-apr-8085-exec-38
card...余额：2700.00
存折...取出：200...http-apr-8085-exec-104
存折...余额：2500.00
存折...取出：200...http-apr-8085-exec-73
存折...余额：2300.00
存折...取出：200...http-apr-8085-exec-105
存折...余额：2100.00
存折...取出：200...http-apr-8085-exec-120
存折...余额：1900.00
存折...取出：200...http-apr-8085-exec-39
存折...余额：1700.00
存折...取出：200...http-apr-8085-exec-107
存折...余额：1500.00
card...取出：150...http-apr-8085-exec-108
card...余额：1350.00
card...取出：150...http-apr-8085-exec-116
card...余额：1200.00
card...取出：150...http-apr-8085-exec-117
card...余额：1050.00
存折...取出：200...http-apr-8085-exec-111
存折...余额：850.00
存折...取出：200...http-apr-8085-exec-119
存折...余额：650.00
存折...取出：200...http-apr-8085-exec-115
存折...余额：450.00
存折...取出：200...http-apr-8085-exec-123
存折...余额：250.00
存折...取出：200...http-apr-8085-exec-54
存折...余额：50.00
账户余额不足！余额=50.00
账户余额不足！余额=50.00
账户余额不足！余额=50.00
账户余额不足！余额=50.00
账户余额不足！余额=50.00
账户余额不足！余额=50.00
账户余额不足！余额=50.00
账户余额不足！余额=50.00
账户余额不足！余额=50.00
账户余额不足！余额=50.00
账户余额不足！余额=50.00
账户余额不足！余额=50.00
...余额：50.00
...余额：50.00
...余额：50.00
...余额：50.00
账户余额不足！余额=50.00
账户余额不足！余额=50.00
账户余额不足！余额=50.00
账户余额不足！余额=50.00
...余额：50.00
...余额：50.00
...余额：50.00
账户余额不足！余额=50.00
账户余额不足！余额=50.00
账户余额不足！余额=50.00
...余额：50.00
...余额：50.00
...余额：50.00
账户余额不足！余额=50.00
账户余额不足！余额=50.00
账户余额不足！余额=50.00
...余额：50.00
...余额：50.00
...余额：50.00
账户余额不足！余额=50.00
...余额：50.00
...余额：50.00
...余额：50.00
...余额：50.00
...余额：50.00
...余额：50.00
...余额：50.00
...余额：50.00
...余额：50.00
...余额：50.00
账户余额不足！余额=50.00
...余额：50.00
...余额：50.00
...余额：50.00
...余额：50.00
...余额：50.00
...余额：50.00
...余额：50.00
测试用例：
链接：https://pan.baidu.com/s/1YuH8FTu9SX4DxVYNaOL9Lg 密码：4vgr