一.商品减库中存在问题
1.传统的代码
1.1引入jar包
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-redis</artifactId>
</dependency>
<dependency>
<groupId>org.redisson</groupId>
<artifactId>redisson</artifactId>
<version>3.6.5</version>
</dependency>
<dependency>
<groupId>redis.clients</groupId>
<artifactId>jedis</artifactId>
<version>2.9.0</version>
</dependency>
1.2配置application.yml
server:
port: 8090
spring:
redis:
host: 192.168.2.66
port: 6379
1.3原始测试代码
package com.redisson;
import org.redisson.Redisson;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.redis.core.RedisTemplate;
import org.springframework.data.redis.core.StringRedisTemplate;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
@RestController
@RequestMapping("/test")
public class TestDeductController {
@Autowired
private Redisson redisson;
@Autowired
private StringRedisTemplate stringRedisTemplate;
@Autowired
private RedisTemplate redisTemplate;
@RequestMapping("/deduct_stock")
public String deductStock() {
int stock = Integer.parseInt(stringRedisTemplate.opsForValue().get("stock")); // jedis.get("stock")
if (stock > 0) {
int realStock = stock - 1;
stringRedisTemplate.opsForValue().set("stock", realStock + ""); // jedis.set(key,value)
System.out.println("扣减成功，剩余库存:" + realStock);
} else {
System.out.println("扣减失败，库存不足");
}
return "end";
}
}
1.apache-jmeter测试工具的使用
2.配置nginx代理，修改nginx-1.10.2/conf/nginx.conf，并启动
upstream redislock{
server 192.168.2.100:8080 weight=1;
server 192.168.2.100:8090 weight=1;
}
server {
listen 80;
server_name localhost;
#charset koi8-r;
#access_log logs/host.access.log main;
location / {
root html;
index index.html index.htm;
proxy_pass http://redislock;
}
}
3创建8080,8090spring boot后端客户端
4.测试结果
说明：当多个客户端同时访问这个减库存的逻辑的时候，会出现多个客户端获取的库存数据是一样的，这样导致库存的实际的扣减值和库存值不一致。
1.4使用synchronized进行代码优化
package com.redisson;
import org.redisson.Redisson;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.redis.core.RedisTemplate;
import org.springframework.data.redis.core.StringRedisTemplate;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
@RestController
@RequestMapping("/test")
public class TestDeductController {
@Autowired
private Redisson redisson;
@Autowired
private StringRedisTemplate stringRedisTemplate;
@Autowired
private RedisTemplate redisTemplate;
@RequestMapping("/deduct_stock")
public String deductStock() {
synchronized (this){
int stock = Integer.parseInt(stringRedisTemplate.opsForValue().get("stock")); // jedis.get("stock")
if (stock > 0) {
int realStock = stock - 1;
stringRedisTemplate.opsForValue().set("stock", realStock + ""); // jedis.set(key,value)
System.out.println("扣减成功，剩余库存:" + realStock);
} else {
System.out.println("扣减失败，库存不足");
}
return "end";
}
}
}
说明：当存在多台后端服务器时，synchronized也会失效，因为synchronized针对的是单台服务器加锁，出现多台服务器，就不能够很好的实现库存加锁。
1.5设置一个锁，程序解锁后或超时的后删除锁
package com.redisson;
import org.redisson.Redisson;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.redis.core.RedisTemplate;
import org.springframework.data.redis.core.StringRedisTemplate;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import java.util.UUID;
import java.util.concurrent.TimeUnit;
@RestController
@RequestMapping("/test")
public class TestDeductController {
@Autowired
private Redisson redisson;
@Autowired
private StringRedisTemplate stringRedisTemplate;
@Autowired
private RedisTemplate redisTemplate;
@RequestMapping("/deduct_stock")
public String deductStock() {
String lockKey = "lock:product_101";
String clientId = UUID.randomUUID().toString();
Boolean result = stringRedisTemplate.opsForValue().setIfAbsent(lockKey, clientId, 30, TimeUnit.SECONDS); //jedis.setnx(k,v)
if (!result) {
return "error_code";
}
try {
int stock = Integer.parseInt(stringRedisTemplate.opsForValue().get("stock")); // jedis.get("stock")
if (stock > 0) {
int realStock = stock - 1;
stringRedisTemplate.opsForValue().set("stock", realStock + ""); // jedis.set(key,value)
System.out.println("扣减成功，剩余库存:" + realStock);
} else {
System.out.println("扣减失败，库存不足");
}
return "end";
} finally {
if (clientId.equals(stringRedisTemplate.opsForValue().get(lockKey))) {
stringRedisTemplate.delete(lockKey);
}
}
}
}
说明：以上情况依然会出现一个问题，当在执行在finally行是，刚刚判断完成，此时的超时的时间到了，此后删除锁不是自身加的锁而是，后面线程加的锁，此后的过程都会删除后面线程的加的锁，依然存在bug
1.6最终优化方案
1.导入jar包
<dependency>
<groupId>org.redisson</groupId>
<artifactId>redisson</artifactId>
<version>3.6.5</version>
</dependency>
2.在启动项中配置redisson
@Bean
public Redisson redisson() {
// 此为单机模式
Config config = new Config();
config.useSingleServer().setAddress("redis://192.168.2.66:6379").setDatabase(0);
return (Redisson) Redisson.create(config);
}
3.优化代码程序
package com.redisson;
import org.redisson.Redisson;
import org.redisson.api.RLock;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.redis.core.RedisTemplate;
import org.springframework.data.redis.core.StringRedisTemplate;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import java.util.UUID;
import java.util.concurrent.TimeUnit;
@RestController
@RequestMapping("/test")
public class TestDeductController {
@Autowired
private Redisson redisson;
@Autowired
private StringRedisTemplate stringRedisTemplate;
@Autowired
private RedisTemplate redisTemplate;
@RequestMapping("/deduct_stock")
public String deductStock() {
String lockKey = "lock:product_101";
//获取锁对象
RLock redissonLock = redisson.getLock(lockKey);
//加分布式锁
redissonLock.lock();
try {
int stock = Integer.parseInt(stringRedisTemplate.opsForValue().get("stock")); // jedis.get("stock")
if (stock > 0) {
int realStock = stock - 1;
stringRedisTemplate.opsForValue().set("stock", realStock + ""); // jedis.set(key,value)
System.out.println("扣减成功，剩余库存:" + realStock);
} else {
System.out.println("扣减失败，库存不足");
}
return "end";
} finally {
redissonLock.unlock();
}
}
}
