Preload data from CSV and refresh after Xmin.

[xhadev]

Hello,
I'm trying to work on solution based on CSV stored in a server( I can't use a database) that will hold the key/value data, that I need to load when my app start, that seems pretty straightforward with a bulkload approach but my problem is that after Xmin I want to refresh the whole cache a reload the CSV to fetch the latest values again, the CSV can change frequently. My problem is that the data is from a CSV so I don't have a single item load from a service/db other than my cache.

I know I can use a simple ConcurrentHashMap but I want to leverage the power off caffeine.

Note: I started my journey trying to use Guava, but guavaAsyncLoader forces you to implement load
public Boolean load(@Nonnull String key) and I don't have a single load because the data is in the CSV. I just want that
.refreshAfterWrite(10, TimeUnit.MINUTES) will trigger a bulk load.

Thanks.

[ben-manes]

In these cases it is typically better to forgo a caching library and use a scheduled task to periodically replace an unmodifiable map. This is simple to reason about, works as desired, and requires no dependencies. For example,

private volatile Map<String, String> cityToState;

CsvCache(ScheduledExecutorService executor) {
  executor.scheduleAtFixedRate(this::reload, 10, 10, TimeUnit.MINUTES);
  reload();
}

private reload() {
  cityToState = parseCsv().stream()
      .collect(toUnmodifiableMap(row -> row.get("city"), row -> row.get("state"));
}

public Optional<String> getStateForCity(String city) {
  return Optional.ofNullable(cityToState.get(city));
}