Last updated: February 26, 2023
In this tutorial, we do caching for some basic real-world examples. Notably, we’ll demonstrate how we can configure this caching mechanism to be time-limited. We also refer to such time-limitation as time-to-live (TTL) for a cache.
Previously, we have demonstrated how we can use @Cacheable annotation from Spring. Meanwhile, a practical use case for caching is when a Hotel booking website’s main page is opened frequently. This means that the REST endpoint for providing a list of Hotels is requested often, making frequent calls to the database. Database calls are slower as compared to providing data directly from memory.
First, we’ll create SpringCachingConfig:
@Configuration
@EnableCaching
public class SpringCachingConfig {
@Bean
public CacheManager cacheManager() {
return new ConcurrentMapCacheManager("hotels");
}
}We also need SpringCacheCustomizer:
@Component
public class SpringCacheCustomizer implements CacheManagerCustomizer<ConcurrentMapCacheManager> {
@Override
public void customize(ConcurrentMapCacheManager cacheManager) {
cacheManager.setCacheNames(asList("hotels"));
}
}After setup, we are able to make use of Spring configuration. We can reduce the REST endpoint response time by storing the Hotel objects in memory. We use theĀ @Cacheable annotation for caching a list of Hotel objects as in the code snippet below:
@Cacheable("hotels")
public List<Hotel> getAllHotels() {
return hotelRepository.getAllHotels();
}However, the cached Hotels list may change in the database over time due to updates, deletions, or additions. We want to refresh the cache by setting a time-to-live interval (TTL), after which the existing cache entries are removed and refilled upon the first call of the method in Section 3 above.
We can do this by making use of @CacheEvict annotation. For instance, in the example below, we set the TTL through caching.spring.hotelListTTL variable:
@CacheEvict(value = "hotels", allEntries = true)
@Scheduled(fixedRateString = "${caching.spring.hotelListTTL}")
public void emptyHotelsCache() {
logger.info("emptying Hotels cache");
}We want the TTL to be 12 hours. The value in terms of milliseconds turns out to be 12 x 3600 x 1000 = 43200000. We define this in environment properties. Additionally, if we are using a properties-based environment configuration, we can set the cache TTL as follows:
caching.spring.hotelListTTL=43200000Alternatively, if we are using a YAML-based design, we can set it as:
caching:
spring:
hotelListTTL: 43200000In this article, we explored how to set TTL caching for Spring-based caching. As always, we can find the complete code over on GitHub.
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