设计模式之模板模式

改造之前

 @Override
    public User selectUserById(Integer id) {
        User  user = (User) redisTemplate.opsForValue().get("user:" + id);
        if (user == null) {
            synchronized (this) {
                user = (User ) redisTemplate.opsForValue().get("user:" + id);
                if (user == null) {
                    user = getById(id);
                    redisTemplate.opsForValue().set("user:" + id, user, 10, TimeUnit.MINUTES);
                }
            }
        }
        return user;
    }

组件定义

@Component
public class RedisCacheTemplate {

    @Autowired
    private RedisTemplate redisTemplate;


    /**
     * @param key            redis键
     * @param expireTime     过期时间
     * @param serviceHandler 处理类
     * @return T
     */
    public <T> T loadCache(String key, long expireTime, BaseServiceHandler<T> serviceHandler) {
        return getCacheFromRedis(key, expireTime, TimeUnit.MINUTES, serviceHandler);
    }


    /**
     * @param key            redis键
     * @param expireTime     过期时间
     * @param timeUnit       时间单位
     * @param serviceHandler 处理类
     * @return T
     */
    public <T> T loadCache(String key, long expireTime, TimeUnit timeUnit, BaseServiceHandler<T> serviceHandler) {
        return getCacheFromRedis(key, expireTime, timeUnit, serviceHandler);
    }

    private <T> T getCacheFromRedis(final String key, long expireTime, TimeUnit timeUnit, BaseServiceHandler<T> serviceHandler) {
        T result = (T) redisTemplate.opsForValue().get(key);
        if (result == null) {
            synchronized (key) {
                result = (T) redisTemplate.opsForValue().get(key);
                if (result == null) {
                    result = serviceHandler.loadData();
                    expireTime = getExpireTime(expireTime);
                    redisTemplate.opsForValue().set(key, result, expireTime, timeUnit);
                }
            }
        }
        return result;
    }

    private  long getExpireTime(long expireTime) {
        LongStream longs = ThreadLocalRandom.current().longs(1, 5, 16);
        long randLong = longs.min().getAsLong();
        return (expireTime + randLong);
    }
}

服务处理类定义

@FunctionalInterface
public interface BaseServiceHandler<T> {

    /**
     * 加载数据
     * @return T
     */
    T loadData();
}

调用模板方法(改造之后)

 @Override
    public User findById(Long id) {
        User user = redisCacheTemplate.loadCache("user:"+String.valueOf(id), 20, TimeUnit.SECONDS, () -> {
            return userMapper.selectByPrimaryKey(id);
        });
        return user;
    }