并发实际场景（保持余额操作的正确）

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。

例子（线程不安全）：

控制器代码：

@Controller
public class TestController {// 开个银行帐号Acount3 account = new Acount3();@RequestMapping(value="/cardAddAcount")@ResponseBodypublic TaotaoResult cardAddAcount(){TaotaoResult result = new TaotaoResult();result.setData("+100, 余额： " + account.addAcount("card", 100));return  result;}@RequestMapping(value="/passbookAddAcount")@ResponseBodypublic TaotaoResult passbookAddAcount(){TaotaoResult result = new TaotaoResult();result.setData("+100, 余额： " + account.addAcount("存折", 100));return  result;}@RequestMapping(value="/cardSubAcount")@ResponseBodypublic TaotaoResult cardSubAcount(){TaotaoResult result = new TaotaoResult();result.setData("-150, 余额： " + account.subAcount("card", 150));return  result;}@RequestMapping(value="/passbookSubAcount")@ResponseBodypublic TaotaoResult passbookSubAcount(){TaotaoResult result = new TaotaoResult();result.setData("-200, 余额： " + account.subAcount("存折", 200));return  result;}@RequestMapping(value="/selectAcount")@ResponseBodypublic TaotaoResult selectAcount(){TaotaoResult result = new TaotaoResult();result.setData(account.selectAcount(""));return  result;}
}

账户3（线程不安全）：

/*** 银行账户:无任何并发处理** @author Administrator*/
public class Acount3 {private int count = 0;/*** 存钱** @param money*/public int addAcount(String name, int money) {// 存钱count += money;System.out.println(name + "...存入：" + money + "..." + Thread.currentThread().getName());return selectAcount(name);}/*** 取钱** @param money*/public int subAcount(String name, int money) {// 先判断账户现在的余额是否够取钱金额if (count - money < 0) {System.out.println("账户余额不足！余额=" + count);return money;}// 取钱count -= money;System.out.println(name + "...取出：" + money + "..." + Thread.currentThread().getName());return selectAcount(name);}/*** 查询余额*/public int selectAcount(String name) {System.out.println(name + "...余额：" + count);return count;}
}

账户3（线程不安全）执行的结果：

例子2：

账户2（线程安全）：给每个方法加上synchronized 实现

/*** 银行账户：线程安全** @author Administrator*/
public class Acount2 {private int count = 0;/*** 存钱** @param money*/public synchronized int addAcount(String name, int money) {// 存钱count += money;System.out.println(name + "...存入：" + money + "..." + Thread.currentThread().getName());return selectAcount(name);}/*** 取钱** @param money*/public synchronized int subAcount(String name, int money) {// 先判断账户现在的余额是否够取钱金额if (count - money < 0) {System.out.println("账户余额不足！余额=" + count);return money;}// 取钱count -= money;System.out.println(name + "...取出：" + money + "..." + Thread.currentThread().getName());return selectAcount(name);}/*** 查询余额*/public synchronized int selectAcount(String name) {System.out.println(name + "...余额：" + count);return count;}
}

例子1：

账户1（线程安全）：通过lock来实现

import java.util.concurrent.locks.ReentrantLock;/*** 银行账户：线程安全** @author Administrator*/
public class Acount {private int count = 0;private ReentrantLock lock = new ReentrantLock();/*** 存钱** @param money*/public int addAcount(String name, int money) {lock.lock();try {// 存钱count += money;System.out.println(name + "...存入：" + money + "..." + Thread.currentThread().getName());} finally {lock.unlock();}return selectAcount(name);}/*** 取钱** @param money*/public int subAcount(String name, int money) {lock.lock();try {// 先判断账户现在的余额是否够取钱金额if (count - money < 0) {System.out.println("账户余额不足！余额=" + count);return money;}// 取钱count -= money;System.out.println(name + "...取出：" + money + "..." + Thread.currentThread().getName());} finally {lock.unlock();}return selectAcount(name);}/*** 查询余额*/public int selectAcount(String name) {lock.lock();try {System.out.println(name + "...余额：" + count);} finally {lock.unlock();}return count;}
}

代码demo：

链接：https://pan.baidu.com/s/1i_uzZKd-GC-8NPa1hFdw8w 密码：rht7

测试用例：

链接：https://pan.baidu.com/s/1Ri54rR1k7JETO6i5pDyVlw 密码：u96e

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