java 38 lines · 7 steps

Warming a Spring cache at startup

A Spring bean pre-loads a cache once all singletons are ready, so the first real request doesn't pay the cold-start cost.

Explained by highlit

Spring Intermediate caching startup-hook dependency-injection resilience lifecycle

1@Component
2public class RegionCacheWarmer implements SmartInitializingSingleton {
3 
  private static final Logger log = LoggerFactory.getLogger(RegionCacheWarmer.class);
5 
  private final RegionService regionService;
  private final CacheManager cacheManager;
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  public RegionCacheWarmer(RegionService regionService, CacheManager cacheManager) {
      this.regionService = regionService;
      this.cacheManager = cacheManager;
  }
13 
  @Override
  public void afterSingletonsInstantiated() {
      Cache cache = cacheManager.getCache("regions");
      if (cache == null) {
          log.warn("Cache 'regions' is not configured; skipping warm-up");
          return;
      }
21 
      StopWatch watch = new StopWatch();
      watch.start();
24 
      List<String> codes = regionService.findActiveRegionCodes();
      for (String code : codes) {
          try {
              regionService.getRegionByCode(code);
          } catch (Exception ex) {
              log.error("Failed to warm cache entry for region '{}'", code, ex);
          }
      }
33 
      watch.stop();
      log.info("Warmed 'regions' cache with {} entries in {} ms",
              codes.size(), watch.getTotalTimeMillis());
  }
38}

01 / 01

STEP 01

Walkthrough

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Three takeaways

1SmartInitializingSingleton runs code after the whole context is built, making it ideal for cross-bean startup tasks.
2Guarding against a missing cache lets warm-up degrade gracefully instead of crashing the application.
3Isolating each entry's fetch in a try/catch keeps one bad record from aborting the entire warm-up.

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