Spring Cache — @Cacheable Kimin Cevabını Hatırlıyor?

1
@Configuration
2
@EnableCaching
3
class CacheConfig implements CachingConfigurer {
4

5
    @Bean
6
    RedisCacheManager cacheManager(RedisConnectionFactory connections) {
7
        var json = RedisSerializationContext.SerializationPair
8
                .fromSerializer(new GenericJackson2JsonRedisSerializer());
9

10
        var defaults = RedisCacheConfiguration.defaultCacheConfig()
11
                .entryTtl(Duration.ofMinutes(10))
12
                .disableCachingNullValues()
13
                .serializeValuesWith(json);
14

15
        return RedisCacheManager.builder(connections)
16
                .cacheDefaults(defaults)
17
                // A displayed rate must never be far behind the treasury desk,
18
                // even if an evict is ever missed.
19
                .withCacheConfiguration("fxRates", defaults.entryTtl(Duration.ofSeconds(15)))
20
                // Defer put/evict until the surrounding transaction commits.
21
                .transactionAware()
22
                .build();
23
    }
24

25
    // Redis down: log it and fall through to the database instead of failing the request.
26
    @Override
27
    public CacheErrorHandler errorHandler() {
28
        return new LoggingCacheErrorHandler();
29
    }
30
}

1
@Service
2
class FxRateBoard {
3

4
    private final FxRateRepository rates;
5

6
    FxRateBoard(FxRateRepository rates) {
7
        this.rates = rates;
8
    }
9

10
    // Channel is in the key because the spread differs: forget it and mobile
11
    // customers see the branch's rate, or the other way round.
12
    @Cacheable(cacheNames = "fxRates", key = "#pair + ':' + #channel", sync = true)
13
    public FxRateView rateOf(CurrencyPair pair, Channel channel) {
14
        FxRate rate = rates.findCurrent(pair).orElseThrow(() -> new RateNotFoundException(pair));
15
        return FxRateView.of(rate, channel);
16
    }
17
}

1
@Service
2
class TreasuryRateService {
3

4
    private final FxRateRepository rates;
5

6
    TreasuryRateService(FxRateRepository rates) {
7
        this.rates = rates;
8
    }
9

10
    // Transaction-aware cache manager: these evicts run after COMMIT, not when the
11
    // method returns, so a concurrent reader cannot re-cache the old rate.
12
    @Transactional
13
    @Caching(evict = {
14
            @CacheEvict(cacheNames = "fxRates", key = "#pair + ':MOBILE'"),
15
            @CacheEvict(cacheNames = "fxRates", key = "#pair + ':BRANCH'")})
16
    public void publish(CurrencyPair pair, BigDecimal mid) {
17
        rates.findCurrent(pair).orElseThrow().retire();   // history is kept, never overwritten
18
        rates.save(FxRate.published(pair, mid));
19
    }
20
}

1
// Immutable on purpose: a local cache would hand the same instance to every caller.
2
public record FxRateView(String pair, String channel, BigDecimal buy, BigDecimal sell, Instant publishedAt) {
3

4
    static FxRateView of(FxRate rate, Channel channel) {
5
        BigDecimal spread = channel.spread();                 // e.g. wider at the branch
6
        return new FxRateView(rate.getPair().code(), channel.name(),
7
                rate.getMid().subtract(spread).setScale(4, RoundingMode.DOWN),
8
                rate.getMid().add(spread).setScale(4, RoundingMode.UP),
9
                rate.getPublishedAt());
10
    }
11
}

1
@RestController
2
@RequestMapping("/fx")
3
class FxController {
4

5
    private final FxRateBoard board;
6
    private final FxQuotes quotes;
7

8
    FxController(FxRateBoard board, FxQuotes quotes) {
9
        this.board = board;
10
        this.quotes = quotes;
11
    }
12

13
    // The rate board: a few seconds stale is fine, so it comes from the cache.
14
    @GetMapping("/rates/{pair}")
15
    FxRateView rate(@PathVariable CurrencyPair pair, @RequestParam Channel channel) {
16
        return board.rateOf(pair, channel);    // a separate bean: the call goes through the proxy
17
    }
18

19
    // Before buying, the customer gets a quote locked for a short time. The exchange
20
    // executes at the quote's rate, never at whatever the cache holds by then.
21
    @PostMapping("/quotes")
22
    FxQuote quote(@RequestBody @Valid QuoteRequest body) {
23
        return quotes.lock(body.pair(), body.channel(), body.amount());
24
    }
25
}

1
spring:
2
  cache:
3
    type: redis
4
    cache-names: fxRates          # created up front, so they appear in metrics immediately
5
  data:
6
    redis:
7
      host: redis
8
      port: 6379
9
      timeout: 200ms             # a slow cache must not become a slow rate board
10

11
management:
12
  endpoints:
13
    web:
14
      exposure:
15
        include: health,metrics,caches