Question

我需要以不同的间隔检查一些端点，因此我设置了Caffeine的缓存生成器。

this.localeWeatherCache = newBuilder().build();

this.currentWeatherCache=newBuilder().expireAfterWrite(Duration.ofHours(3)).build();

this.weatherForecastsCache = newBuilder().expireAfterWrite(Duration.ofHours(12)).build();

在我的服务中，我将这3个终结点称为“端点”，最后，我将在Mono.zip（）中返回包含所有详细信息的对象。

在测试期间，我注意到 climaTempoRepository.findLocaleByCityNameAndState被执行了两次，并且在 currentWeather 缓存过期后，它再次调用了 locale 端点，weatherForecast也会发生同样的情况，它再次调用语言环境。

为什么失败？它不应该使用缓存吗？还是我做的方法是错误的？

任何帮助或指针都将不胜感激！：）

public Mono<Weather> weatherForecastByLocation(Location location) {

    Mono<ClimaTempoLocale> locale =
            CacheMono.lookup(key ->
                    Mono.justOrEmpty(localeWeatherCache.getIfPresent(key))
                            .map(Signal::next), location)
                    .onCacheMissResume(() -> climaTempoRepository.findLocaleByCityNameAndState(location.city(), location.state()))
                    .andWriteWith((key, signal) -> Mono.fromRunnable(() ->
                            Optional.ofNullable(signal.get())
                                    .ifPresent(value -> localeWeatherCache.put(key, value))));

    Mono<CurrentWeather> currentWeather =
            CacheMono.lookup(key ->
                    Mono.justOrEmpty(currentWeatherCache.getIfPresent(key))
                            .map(Signal::next), location)
                    .onCacheMissResume(() -> locale.flatMap(climaTempoRepository::findCurrentWeatherByLocale)
                            .subscribeOn(Schedulers.elastic()))
                    .andWriteWith((key, signal) -> Mono.fromRunnable(() ->
                            Optional.ofNullable(signal.get())
                                    .ifPresent(value -> currentWeatherCache.put(key, value))));

    Mono<WeatherForecasts> weatherForecasts =
            CacheMono.lookup(key ->
                    Mono.justOrEmpty(weatherForecastsCache.getIfPresent(key))
                            .map(Signal::next), location)
                    .onCacheMissResume(() -> locale.flatMap(climaTempoRepository::findDailyForecastByLocale)
                            .subscribeOn(Schedulers.elastic()))
                    .andWriteWith((key, signal) -> Mono.fromRunnable(() ->
                            Optional.ofNullable(signal.get())
                                    .ifPresent(value -> weatherForecastsCache.put(key, value))));

    return Mono.zip(currentWeather,
            weatherForecasts,
            (current, forecasts) ->
                    Weather.buildWith(builder -> {
                        builder.location = location;
                        builder.currentWeather = current;
                        builder.weatherForecasts = forecasts;
                    }));

}

Answer 1

AsyncLoadingCache可以从键中计算值，并返回结果的CompletableFuture。可以将其转换为Mono的{{1}}方法。这样可以确保只对给定密钥进行一次执行，而不会因将期货存储在缓存中而阻塞。

fromFuture

Answer 2

https://stackoverflow.com/a/52803247/11209784中的示例ClimaTempoLocale可以如下计算：

Cache<Location, ClimaTempoLocale> weatherLocaleCache = Caffeine.newBuilder().build();

private Mono<ClimaTempoLocale> findLocale(Location location) {
    Mono<ClimaTempoLocale> locale;
    ClimaTempoLocale cachedLocale = weatherLocaleCache.getIfPresent(location);
    if (cachedLocale != null) {
        locale = Mono.just(cachedLocale);
    } else {
        locale = climaTempoRepository.findLocaleByCityNameAndState(location.city(), location.state())
                .doOnNext(climaTempoLocale -> weatherLocaleCache.put(location, climaTempoLocale));
    }

    return locale;
}

副作用是当并发调用导致高速缓存未命中时，可能会连续写入同一密钥。

这样做，依赖ClimaTempoLocale的调用可以以相同的方式继续：

Cache<Location, CurrentWeather> currentWeatherCache = Caffeine.newBuilder().expireAfterWrite(Duration.ofHours(3)).build();

Cache<Location, WeatherForecasts> weatherForecastsCache = Caffeine.newBuilder().expireAfterWrite(Duration.ofHours(12)).build();

public Mono<Weather> weatherForecastByLocation(Location location) {
    Mono<ClimaTempoLocale> locale = findLocale(location);

    Mono<CurrentWeather> currentWeather =
            CacheMono.lookup(
                    key -> Mono.justOrEmpty(currentWeatherCache.getIfPresent(key))
                            .map(Signal::next),
                    location)
                    .onCacheMissResume(
                            () -> locale.flatMap(climaTempoRepository::findCurrentWeatherByLocale)
                                    .subscribeOn(Schedulers.elastic()))
                    .andWriteWith(
                            (key, signal) -> Mono.fromRunnable(
                                    () -> Optional.ofNullable(signal.get())
                                            .ifPresent(value -> currentWeatherCache.put(key, value))));

    Mono<WeatherForecasts> weatherForecasts =
            CacheMono.lookup(
                    key -> Mono.justOrEmpty(weatherForecastsCache.getIfPresent(key))
                            .map(Signal::next),
                    location)
                    .onCacheMissResume(
                            () -> locale.flatMap(climaTempoRepository::findDailyForecastByLocale)
                                    .subscribeOn(Schedulers.elastic()))
                    .andWriteWith(
                            (key, signal) -> Mono.fromRunnable(
                                    () -> Optional.ofNullable(signal.get())
                                            .ifPresent(value -> weatherForecastsCache.put(key, value))));

    return Mono.zip(currentWeather,
            weatherForecasts,
            (current, forecasts) ->
                    Weather.buildWith(builder -> {
                        builder.location = location;
                        builder.currentWeather = current;
                        builder.weatherForecasts = forecasts;
                    }));
}

使用Reactor和Caffeine的缓存无法正常工作

2 个答案: