//根據ID查詢商品
@GetMapping("/{id}")
public R id(@PathVariable String id){
	//先查Redis緩存
	Object o = redisTemplate.opsForValue().get(id);
	if (o != null) {
		//命中緩存
		System.err.println("id:"+id+",命中redis緩存...");
		return R.success(o);
	}

	//緩存未命中 查詢數據庫
	String lockKey = "lock" + id;
	//加鎖，10s后過期
	for (;;) {
		if (redisTemplate.opsForValue().setIfAbsent(lockKey, System.currentTimeMillis(), 10L, TimeUnit.SECONDS)) {
			//加鎖成功的線程,再次檢查
			o = redisTemplate.opsForValue().get(id);
			if (o != null) {
				//命中緩存
				System.err.println("Thread:" + Thread.currentThread().getName() + ",id:"+id+",命中redis緩存...");
				//釋放鎖
				redisTemplate.delete(lockKey);
				return R.success(o);
			}

			//仍未命中
			System.err.println("Thread:" + Thread.currentThread().getName() + ",id:" + id + ",查詢DB...");
			Goods goods = goodsMapper.selectById(id);
			//結果存入Redis
			redisTemplate.opsForValue().set(id, goods);
			//釋放鎖
			redisTemplate.delete(lockKey);
			return R.success(goods);
		}
		//競爭不到鎖，暫時讓出CPU資源
		Thread.yield();
	}
}