如何同步redis过期时间至caffeine

目的

使用caffeine+redis构建二级缓存，并且可以同步过期时间。

1. redis可以视为集中式外部缓存，缓存及ttl只需设置一次；
2. caffeine集成在分布式程序内部，需要通过懒加载同步redis缓存及ttl.

代码实现

import com.github.benmanes.caffeine.cache.Cache;
import com.github.benmanes.caffeine.cache.Caffeine;
import com.github.benmanes.caffeine.cache.Expiry;
import java.util.concurrent.TimeUnit;
import lombok.Getter;
import org.checkerframework.checker.index.qual.NonNegative;
import org.checkerframework.checker.nullness.qual.NonNull;
import org.redisson.api.RedissonClient;

@Getter
public class CacheHelper {

  private Cache<String, Object> localCache;
  private RedissonClient redissonClient;

  public CacheHelper(RedissonClient redissonClient) {
    this.redissonClient = redissonClient;
    initLocalCache();
  }

  private void initLocalCache() {
    this.localCache = Caffeine.newBuilder().expireAfter(new Expiry<String, Object>() {

      @Override
      public long expireAfterCreate(@NonNull String key, @NonNull Object value, long currentTime) {
        // query ttl by redisson, you can use another redis client instead
        long ttlMillis = redissonClient.getBucket(key).remainTimeToLive();
        return TimeUnit.MILLISECONDS.toNanos(Math.max(ttlMillis, 0));
      }

      @Override
      public long expireAfterUpdate(@NonNull String key, @NonNull Object value, long currentTime,
          @NonNegative long currentDuration) {
        return currentDuration;
      }

      @Override
      public long expireAfterRead(@NonNull String key, @NonNull Object value, long currentTime,
          @NonNegative long currentDuration) {
        return currentDuration;
      }
    }).build(key -> redissonClient.getBucket(key).get());
  }

}