第一種:使用synchronized(只適用於單個tomcat)
@Autowired
private StringRedisTemplate stringRedisTemplate;
@GetMapping("/deduct")
public String toDeduct(){
synchronized (this) {
int stock = Integer.parseInt(stringRedisTemplate.opsForValue().get("stock"));
if (stock > 0) {
Long stock1 = stringRedisTemplate.opsForValue().decrement("stock");
System.out.println("扣減成功,剩餘庫存:" + stock1);
}else{
System.out.println("扣減失敗,庫存不足");
}
return "end";
}
}
第二種:使用SETNX命令(多臺tomcat)
@GetMapping("/deduct_stock")
public String deductStock() throws InterruptedException {
String lockKey = "lockKey";
//設計唯一key值防止鎖失效問題
String clientId = UUID.randomUUID().toString();
//設計鎖超時時間,防止服務器宕機時鎖沒有釋放掉(finally語句沒有執行)
Boolean result = stringRedisTemplate.opsForValue().
setIfAbsent(lockKey, clientId, 10, TimeUnit.SECONDS);//jedis.setnx(key,value);
//若鍵 key 已經存在, 則 SETNX 命令不做任何動作。result==false
if (!result) {
return "正在排隊。。。";
}
try {
int stock = Integer.parseInt(stringRedisTemplate.opsForValue().get("stock"));
if (stock > 0) {
Long realStock = stringRedisTemplate.opsForValue().decrement("stock");
System.out.println("扣減成功,剩餘庫存:" + realStock);
}else{
System.out.println("扣減失敗,庫存不足");
}
} finally {
//防止鎖失效問題,在多線程的情況下,每個線程只釋放自己創建的鎖,線程之間互不干預。
if(clientId.equals(stringRedisTemplate.opsForValue().get(lockKey))) {
stringRedisTemplate.delete(lockKey);
}
}
return "end";
}
第三種:使用Redission框架(原理跟第二種一樣)
1、配置config類
@Configuration
public class RedissonConfig {
@Value("${spring.redis.host}")
private String host;
@Value("${spring.redis.port}")
private String port;
@Value("${spring.redis.password}")
private String password;
@Bean
public RedissonClient getRedisson(){
Config config = new Config();
config.useSingleServer().setAddress("redis://" + host + ":" + port).setPassword(password);
//添加主從配置
// config.useMasterSlaveServers().setMasterAddress("").setPassword("").addSlaveAddress(new String[]{"",""});
return Redisson.create(config);
}
}
@GetMapping("/deduct_stock1")
public String deductStock1(){
String lockKey = "lockKey";
RLock redissonLock = redisson.getLock(lockKey);
try {
redissonLock.lock();
int stock = Integer.parseInt(stringRedisTemplate.opsForValue().get("stock"));
if (stock > 0) {
Long realStock = stringRedisTemplate.opsForValue().decrement("stock");
System.out.println("扣減成功,剩餘庫存:" + realStock);
}else{
System.out.println("扣減失敗,庫存不足");
}
} finally {
redissonLock.unlock();
}
return "end";
}
Redission原理:
Redission使用了Lua 腳本,實現原理跟原理跟第二種差不多。
當業務代碼處理時間很長,像mysql慢查詢等等,可以在try代碼塊中每隔10秒檢查是否還持有鎖,如果持有則延長鎖的時間,防止還沒執行完業務代碼“lockKey”就到了失效時間。
測試環境搭建
Redis命令大全
設置Redis密碼
pom:
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-redis</artifactId>
</dependency>
<dependency>
<groupId>org.redisson</groupId>
<artifactId>redisson</artifactId>
<version>3.5.7</version>
</dependency>
application.properties:
server.port=8090
# redis
spring.redis.host=127.0.0.1
spring.redis.port=6379
spring.redis.password=888888
spring.redis.jedis.pool.max-active=500
spring.redis.jedis.pool.max-idle=1000
spring.redis.jedis.pool.max-wait=6000ms
spring.redis.jedis.pool.min-idle=4
Nginx負載均衡:
upstream redislock{
server 127.0.0.1:8080 weight = 1;
server 127.0.0.1:8090 weight = 1;
}
server {
listen 80;
server_name localhost;
location / {
root html;
index index.html index.htm;
proxy_pass http://redislock;
}
}
Jmeter壓力測試
發送http請求:
設置發送地址:
表示在0秒內發送200個請求,處理完後再發送200 * 3次,總計200 * 4次請求:
結果集:
測試結果:
沒有出現超賣問題