Simple caching with a TTL

Spring's cache abstraction framework is hugely useful for declarative caching as outlined in previous posts. As we start to use more caches, an inherent requirement that arises is periodic and on-demand purging. For the first kind of purge, you require a Time To Live (TTL) to be associated with your cache. External solutions like ehcache provide configuration to be able to do this. There are host of other parameters, like writing to disk, disk location, buffer sizes, max limits that can be configured using the configuration. However, what if your requirement is simpler and don't want to marry into ehcache just yet.

Spring's ConcurrentMapCacheFactoryBean has been made nicely pluggable where you can plug in any backing store that you want to use for the concurrent map based caching. So, here we can plug in our own TTLAwareConcurrentMap. But, I don't want to write TTL logic myself, right? Sure, just use the constructs available from guava. Guava gives a TTL backed map with a CacheBuilder which looks as simple as:

return CacheBuilder.newBuilder().expireAfterWrite(duration, unit).build().asMap();

All we need to do now is create a FactoryBean in Spring that will be injected with the duration (and unit of the duration) of the TTL and it will vend out the store that will be used by Spring's caching framework. Sample FactoryBean isTTLAwareConcurrentMapFactoryBean.

For on-demand spring cache flushes, we can have a JMX operation defined on a custom CacheManager that is injected with the Spring caches at startup. On invocation, the specific cache or all caches may be flushed by invoking the Cache.clear() method. Due credit to this SO question.

Hope this helps!

References:

• http://docs.spring.io/spring/docs/3.2.2.RELEASE/spring-framework-reference/html/cache.html
• http://stackoverflow.com/questions/8181768/can-i-set-a-ttl-for-cacheable
• http://docs.guava-libraries.googlecode.com/git/javadoc/com/google/common/cache/CacheBuilder.html
• http://docs.spring.io/spring/docs/3.1.x/javadoc-api/org/springframework/cache/concurrent/ConcurrentMapCacheFactoryBean.html
• https://github.com/kilokahn/spring-testers/tree/master/spring-cache-tester