基于redis实现分布式锁的原理与方法

/**
 * @author 张新华
 * @version V1.0
 * @Package com.ay.framework.order.redis.product
 * @date 2020年03月26日, 0026 10:29
 * @Copyright © 2020 安元科技有限公司
 */
@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
public @interface StockLock {

  /**
   * @author zxhtom
   * @Description 锁key的前缀
   * @Date 15:25 2020年03月25日, 0025
   * @Param []
   * @return java.lang.String
   */
  String prefix() default "";
  /**
   * @author zxhtom
   * @Description key的分隔符
   * @Date 15:27 2020年03月25日, 0025
   * @Param []
   * @return java.lang.String
   */
  String delimiter() default ":";
}

/**
 * @author 张新华
 * @version V1.0
 * @Package com.ay.framework.order.redis.product
 * @date 2020年03月26日, 0026 11:09
 * @Copyright © 2020 安元科技有限公司
 */
@Target({ElementType.PARAMETER , ElementType.METHOD , ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
public @interface StockParam {
  /**
  * @author zxhtom
  * @Description 组成key
  * @Date 11:11 2020年03月26日, 0026
  * @Param []
  * @return java.lang.String[]
  */
  String[] names() default {""};
}

@Around("execution(public * *(..)) && @annotation(com.ay.framework.order.redis.product.StockLock)")

RedisAtomicLong entityIdCounter = new RedisAtomicLong(lockKey, redisTemplate.getConnectionFactory());
  if (redisTemplate.hasKey(CoreConstants.UPDATEPRODUCTREDISLOCKKEY + lockKey)) {
    //表示lockKey的库存信息有变动。此时无法进行交易
    throw new BusinessException("库存变动。暂无法交易");
  }
  Long increment = entityIdCounter.decrementAndGet();
  if (increment >= 0) {
    try {
      Object proceed = pjp.proceed();
    } catch (Throwable throwable) {
      //所占资源需要释放回资源池
      while (!redisLock.tryGetLock(CoreConstants.UPDATEPRODUCTREDISLOCKKEY + lockKey, "")) {

      }
      //表示lockKey的库存信息有变动。此时无法进行交易
      long l = entityIdCounter.incrementAndGet();
      if (l < 1) {
        redisTemplate.opsForValue().set(lockKey,1);
      }
      redisLock.unLock(CoreConstants.UPDATEPRODUCTREDISLOCKKEY + lockKey);
      throwable.printStackTrace();
    }
  } else {
    redisTemplate.opsForValue().set(lockKey,0);
    throw new BusinessException("库存不足！无法操作");
  }

public Boolean tryGetLock(String key , String value) {
  return tryGetLock(key, value, -1, TimeUnit.DAYS);
}
public Boolean tryGetLock(String key , String value, Integer expire) {
  return tryGetLock(key, value, expire, TimeUnit.SECONDS);
}
public Boolean tryGetLock(String key , String value, Integer expire , TimeUnit timeUnit) {
  ValueOperations operations = redisTemplate.opsForValue();
  if (operations.setIfAbsent(key, value)) {
    //说明 redis没有该key , 换言之 加锁成功 设置过期时间防止死锁
    if (expire > 0) {
      redisTemplate.expire(key, expire, timeUnit);
    }
    return true;
  }
  return false;
}

public Boolean unLock(String key) {
  return redisTemplate.delete(key);
}

@Component()
@Primary
public class StockKeyGenerator implements CacheKeyGenerator {
  @Override
  public String getLockKey(ProceedingJoinPoint pjp) {
    //获取方法签名
    MethodSignature signature = (MethodSignature) pjp.getSignature();
    Method method = signature.getMethod();
    //获取方法cacheLock注解
    StockLock stockLock = method.getAnnotation(StockLock.class);
    //获取方法参数
    Object[] args = pjp.getArgs();
    Parameter[] parameters = method.getParameters();
    StringBuilder builder = new StringBuilder();
    for (int i = 0; i < parameters.length; i++) {
      StockParam stockParam = parameters[i].getAnnotation(StockParam.class);
      Object arg = args[i];
      if (arg instanceof Map) {
        Map<String, Object> temArgMap = (Map<String, Object>) arg;
        String[] names = stockParam.names();
        for (String name : names) {
          if (builder.length() > 0) {
            builder.append(stockLock.delimiter());
          }
          builder.append(temArgMap.get(name));
        }
      }

    }
    return builder.toString();
  }
}